DEFICIENCY ANEMIA (IRON, VITAMIN B12, FOLIC ACID)

DEFICIENCY ANEMIA (IRON, VITAMIN B12, FOLIC ACID). HEMOLYTIC AND APLASTIC ANEMIA

 

Anemia, definition.

 Anemia may be defined as any condition resulting from a decrease in the total circulating erythrocyte mass. It is diagnosed by the demonstration of below normal values for the hemoglobin concentration, the hematocrit, or erythrocyte count.

According to the World Health Organization (WHO), anemia is defined as a hemoglobin level of less than 13 g/dL in men and less than 12 g/dL in women. The basis of this definition is the average hemoglobin level of healthy individuals.

Anemia is present in adults if the hematocrit is less than 41 % (haemoglobin < 13.5 g/dL) in males or 37 % (haemoglobin < 12 g/dL) in females.

 

2. Clinical manifestations of anemias.

2.1.Anemic syndrome.

Symptoms of anemia are easy fatigability, tachycardia, palpitations, tachypnea on exertion, pallor, malaise, weakness, light-headedness, vertigo, and tinnitus, as well as palpitations, angina, and the symptoms of congestive failure.

In the anemic patient, physical examination may demonstrate a forceful heartbeat, strong peripheral pulses, and a systolic “flow” murmur. The skin and mucous membranes may be pale if the hemoglobin is <80 to 100 g/L (8 to 10 g/dL).

 

Fig. 7. Hemoglobin is the most important component of red blood cells. It is composed of a protein called heme, which binds oxygen. In the lungs, oxygen is exchanged for carbon dioxide.

 2.2. Sideropenic syndrome.

Cheilosis (fissures at the corners of the mouth), fever and koilonychia (spooning of the fingernails) are signs of advanced tissue iron deficiency.

Iron deficiency causes skin and mucosal changes, including a smooth tongue, brittle nails. Dysphagia because of formation of esophageal webs also occurs. Many iron-deficient patients develop pica, craving for specific foods, often not rich in iron.

 

2.3. Neurologic manifestations.

The neurologic manifestations often fail to remit fully on treatment. They begin pathologically with demyelination, followed by axonal degeneration and eventual neuronal death; the final stage, of course, is irreversible. Sites of involvement include peripheral nerves; the spinal cord, where the posterior and lateral columns undergo demyelination; and the cerebrum itself. Signs and symptoms include numbness and paresthesia in the extremities (the earliest neurologic manifestations), weakness, and ataxia. There may be sphincter disturbances. Reflexes may be diminished or increased. The Romberg and Babinski signs may be positive, and position and vibration senses are usually diminished. Disturbances of mentation will vary from mild irritability and forgetfulness to severe dementia or frank psychosis. It should be emphasized that neurologic disease may occur in a patient with a normal hematocrit and normal RBC indexes. Although it has many benefits, folate supplementation of food

The clinical features of cobalamin deficiency involve the blood, the gastrointestinal tract, and the nervous system.

 

2.4. Gastrointestinal manifestations.

The gastrointestinal manifestations reflect the effect of cobalamin deficiency on the rapidly proliferating gastrointestinal epithelium. The patient sometimes complains of a sore tongue, which on inspection will be smooth and beefy red. Anorexia with moderate weight loss may also be evident, possibly accompanied by diarrhea and other gastrointestinal symptoms. These latter manifestations may be caused in part by megaloblastosis of the small intestinal epithelium, which results in malabsorption.

 

2.5. Cytopenic syndrome.

Aplastic anemia can appear with seeming abruptness or have a more insidious onset. Bleeding is the most common early symptom; a complaint of days to weeks of easy bruising, oozing from the gums, nose bleeds, heavy menstrual flow, and sometimes petechiae will have beeoticed. With thrombocytopenia, massive hemorrhage is unusual, but small amounts of bleeding in the central nervous system can result in catastrophic intracranial or retinal hemorrhage. Symptoms of anemia are also frequent, including lassitude, weakness, shortness of breath, and a pounding sensation in the ears. Infection is an unusual first symptom in aplastic anemia (unlike in agranulocytosis, where pharyngitis, anorectal infection, or frank sepsis occur early). A striking feature of aplastic anemia is the restriction of symptoms to the hematologic system, and patients often feel and look remarkably well despite drastically reduced blood counts. Systemic complaints and weight loss should point to other etiologies of pancytopenia. History of drug use, chemical exposure, and preceding viral illnesses must often be elicited with repeated questioning.

 

2.6. Hemolytic syndrome.

The hematologic manifestations are almost entirely the result of anemia, although very rarely purpura may appear, due to thrombocytopenia. Symptoms of anemia may include weakness, light-headedness, vertigo, and tinnitus, as well as palpitations, angina, and the symptoms of congestive failure. On physical examination, the patient with florid cobalamin deficiency is pale, with slightly icteric skin and eyes. Elevated bilirubin levels are related to high erythroid cell turnover in the marrow. The pulse is rapid, and the heart may be enlarged; auscultation will usually reveal a systolic flow murmur.

Hemolytic anemias present in different ways. Some appear suddenly as an acute, self-limited episode of intravascular or extravascular hemolysis, a presentation pattern often seen in patients with autoimmune hemolysis or with inherited defects of the Embden-Myerhof pathway or the glutathione reductase pathway. Patients with inherited disorders of the hemoglobin molecule or red cell membrane generally have a lifelong clinical history typical of the disease process. Those with chronic hemolytic disease, such as hereditary spherocytosis, may actually present not with anemia but with a complication stemming from the prolonged increase in red cell destruction such as aplastic crisis, symptomatic bilirubin gallstones, or splenomegaly.

The differential diagnosis of an acute or chronic hemolytic event requires the careful integration of family history, pattern of clinical presentation, and a number of highly specific laboratory studies. Some of the more common congenital hemolytic anemias may be identified from the red cell morphology, a routine laboratory test such as hemoglobin electrophoresis, or a screen for red cell enzymes. Acquired defects in red cell survival are often immunologically mediated and require the immunoglobulin test or a cold agglutinin titer to detect the presence of hemolytic antibodies or complement-mediated red cell destruction.

With acute hemolytic disease, the signs and symptoms depend on the mechanism that leads to red cell destruction. Intravascular hemolysis with release of free hemoglobin may be associated with acute back pain, free hemoglobin in the plasma and urine, and renal failure. Symptoms associated with more chronic or progressive anemia depend on the age of the patient and the adequacy of blood supply to critical organs. Symptoms associated with moderate anemia include fatigue, loss of stamina, breathlessness, and tachycardia (particularly with physical exertion). However, because of the intrinsic compensatory mechanisms that govern the O2-hemoglobin dissociation curve, the gradual onset of anemiaѕparticularly in young patientsѕmay not be associated with signs or symptoms until the anemia is severe [hemoglobin <70 to 80 g/L (7 to 8 g/dL)]. When anemia develops over a period of days or weeks, the total blood volume is normal to slightly increased and changes in cardiac output and regional blood flow help compensate for the overall loss in O2-carrying capacity. Changes in the position of the O2-hemoglobin dissociation curve account for some of the compensatory response to anemia. With chronic anemia, intracellular levels of 2,3-bisphosphoglycerate (BPG) rise, shifting the dissociation curve to the right and facilitating O2 unloading. This compensatory mechanism can only maintaiormal tissue O2 delivery in the face of a 20 to 30 g/L (2 to 3 g/dL) deficit in hemoglobin concentration. Finally, further protection of O2 delivery to vital organs is achieved by the shunting of blood away from organs that are relatively rich in blood supply, particularly the kidney, gut, and skin.

 

3.       Classification of anemias.

 

Fig. 8. Blood & Lymphocyte Development

 

3.1. Pathogenetic classification

3.2.  Morphogenic classification.

3.3.  International classification.

Initial Classification of Anemia 

Classifying an anemia according to the functional defect in red cell production helps organize the subsequent use of laboratory studies. The three major classes of anemia are:

1) marrow production defects (hypoproliferation),

2) red cell maturation defects (ineffective erythropoiesis),

3) decreased red cell survival (blood loss/hemolysis).

This functional classification of anemia then guides the selection of specific clinical and laboratory studies designed to complete the differential diagnosis and to plan appropriate therapy.

 

Fig. 9. The classification is shown in Fig.

 

 

A hypoproliferative anemia is typically seen with a low reticulocyte production index together with little or no change in red cell morphology (a normocytic, normochromic anemia). Maturation disorders typically have a slight to moderately elevated reticulocyte production index that is accompanied by either macrocytic or microcytic red cell indices. Increased red blood cell destruction secondary to hemolysis results in an increase in the reticulocyte production index to at least three times normal, provided sufficient iron is available for hemoglobin synthesis. Hemorrhagic anemia does not typically result in production indices of more than 2.5 times normal because of the limitations placed on expansion of the erythroid marrow by iron availability.

 

Fig. 10. Sickle cell anemia is an inherited blood disease in which the red blood cells produce abnormal pigment (hemoglobin). The abnormal hemoglobin causes deformity of the red blood cells into crescent or sickle-shapes, as seen in this photomicrograph.

 

Fig. 11. Elliptocytosis is a hereditary disorder of the red blood cells (RBCs). In this condition, the RBCs assume an elliptical shape, rather than the typical round shape.

 

Fig. 12. Spherocytosis is a hereditary disorder of the red blood cells (RBCs), which may be associated with a mild anemia. Typically, the affected RBCs are small, spherically shaped, and lack the light centers seen in normal, round RBCs.

 

 

Fig. 13. Sickle cell anemia is an inherited disorder in which abnormal hemoglobin (the red pigment inside red blood cells) is produced. The abnormal hemoglobin causes red blood cells to assume a sickle shape, like the ones seen in this photomicrograph.

  

Fig. 14. Red blood cells (RBCs) are normally round. In ovalocytosis, the cells are oval. Other conditions that produce abnormally shaped RBCs include spherocytosis and eliptocytosis.

 

Fig. 15. These crescent or sickle-shaped red blood cells (RBCs) are present with Sickle cell anemia, and stand out clearly against the normal round RBCs. These abnormally shaped cells may become entangled and block blood flow in the small blood vessels (capillaries).

 

 

Fig. 16. This photomicrograph of red blood cells (RBCs) shows both sickle-shaped and pappenheimer bodies.

 

Fig. 17. These abnormal red blood cells (RBCs) resemble targets. These cells are seen in association with some forms of anemia, and following the removal of the spleen (splenectomy).

 

 

Fig. 18. Peripheral smear showing multiple inclusion bodies inside the red blood cells.

 

 

4.  Iron deficiency anemia.

4.1.  Negative iron balance.

4.2.  Criteria for iron deficiency anemia.

4.3. Differential diagnosis of the iron deficiency anemia.

4.4.  Treatment of the iron deficiency anemia.

STAGES OF IRON DEFICIENCY

Iron deficiency anemia is the condition in which there is anemia and clear evidence of iron deficiency. However, it is worthwhile to consider the steps by which iron deficiency occurs.

These can be divided into three stages. The first stage is negative iron balance, in which the demands for (or losses of) iron exceed the body’s ability to absorb iron from the diet. This stage can result from a number of physiologic mechanisms including blood loss, pregnancy (in which the demands for red cell production by the fetus outstrip the mother’s ability to provide iron), rapid growth spurts in the adolescent, or inadequate dietary iron intake. Most commonly, the growth needs of the fetus or rapidly growing child exceed the individual’s ability to absorb the iroecessary for hemoglobin synthesis from the diet. Blood loss in excess of 10 to 20 mL of red cells per day is greater than the amount of iron that the gut can absorb from a normal diet. Under these circumstances the iron deficit must be made up by mobilization of iron from RE storage sites. During this period measurements of iron storesѕsuch as the serum ferritin level or the appearance of stainable iron on bone marrow aspirationsѕwill decrease. As long as iron stores are present and can be mobilized, the serum iron, total iron-binding capacity (TIBC), and red cell protoporphyrin levels remain withiormal limits. At this stage, red cell morphology and indices are normal.

When iron stores become depleted, the serum iron begins to fall. Gradually, the TIBC increases, as do red cell protoporphyrin levels. By definition, marrow iron stores are absent when the serum ferritin level <15 ug/L. As long as the serum iron remains within the normal range, hemoglobin synthesis is unaffected despite the dwindling iron stores. Once the transferrin saturation falls to 15 to 20%, hemoglobin synthesis becomes impaired. This is a period of iron-deficient erythropoiesis. Careful evaluation of the peripheral blood smear reveals the first appearance of microcytic cells, and if the laboratory technology is available, one finds hypochromic reticulocytes in circulation. Gradually, the hemoglobin and hematocrit begin to fall, reflecting iron deficiency anemia. The transferrin saturation at this point is 10 to 15%.

When moderate anemia is present (hemoglobin 10-13 g/dL), the bone marrow remains hypoproliferative. With more severe anemia (hemoglobin 7-8 g/dL), hypochromia and microcytosis become more prominent, misshapen red cells (poikilocytes) appear on the blood smear as cigar or pencil-shaped forms and target cells, and the erythroid marrow becomes increasingly ineffective. Consequently, with severe prolonged iron deficiency anemia, erythroid hyperplasia of the marrow develops rather than hypoproliferation.

 

CAUSES OF IRON DEFICIENCY

Conditions that increase demand for iron, increase iron loss, or decrease iron intake, absorption, or use can produce iron deficiency.

 

CLINICAL PRESENTATION OF IRON DEFICIENCY

Certain clinical conditions carry an increased likelihood of iron deficiency. Pregnancy, adolescence, periods of rapid growth, and an intermittent history of blood loss of any kind should alert the clinician to possible iron deficiency. A cardinal rule is that the appearance of iron deficiency in an adult male means gastrointestinal blood loss until proven otherwise. Signs related to iron deficiency depend upon the severity and chronicity of the anemia in addition to the usual signs of anemia–fatigue, pallor, and reduced exercise capacity. Cheilosis (fissures at the corners of the mouth) and koilonychia (spooning of the fingernails) are signs of advanced tissue iron deficiency. The diagnosis of iron deficiency is typically based on laboratory results.

 

Fig. 19. Iron deficiency anemia

LABORATORY IRON STUDIES

Serum Iron and Total Iron-Binding Capacity  The serum iron level represents the amount of circulating iron bound to transferrin. The total iron-binding capacity (TIBC) is an indirect measure of the circulating transferrin. The normal range for the serum iron is 50 to 150 ug/dL; the normal range for TIBC is 300 to 360 ug/dL. Transferrin saturation, which is normally 25 to 50%, is obtained by the following formula: serum ironx 100 : TIBC. Iron deficiency states are associated with saturation levels below 18%. In evaluating the serum iron, the clinician should be aware that there is a diurnal variation in the value. A transferrin saturation rate of >50% indicates that a disproportionate amount of the iron bound to transferrin is being delivered to nonerythroid tissues. If this condition persists for an extended time, tissue iron overload may occur.

Serum Ferritin. Free iron is toxic to cells, and the body has established an elaborate set of protective mechanisms to bind iron in various tissue compartments. Within cells, iron is stored complexed to protein as ferritin or hemosiderin. Apoferritin binds to free ferrous iron and stores it in the ferric state. As ferritin accumulates within cells of the RE system, protein aggregates are formed as hemosiderin. Iron in ferritin or hemosiderin can be extracted for release by the RE cells although hemosiderin is less readily available. Under steady state conditions, the serum ferritin level correlates with total body iron stores; thus, the serum ferritin level is the most convenient laboratory test to estimate iron stores. The normal value for ferritin varies according to the age and gender of the individual (Fig. 1). Adult males have serum ferritin values averaging about 100 ug/L, while adult females have levels averaging 30 ug/L. As iron stores are depleted, the serum ferritin falls to <15 ug/L. Such levels are virtually always diagnostic of absent body iron stores.

Evaluation of Bone Marrow Iron Stores. Although RE cell iron stores can also be estimated from the iron stain of a bone marrow aspirate or biopsy, the measurement of serum ferritin has largely supplanted bone marrow aspirates for determination of storage iron. The serum ferritin level is a better indicator of iron overload than the marrow iron stain. However, in addition to storage iron the marrow iron stain provides information about the effective delivery of iron to developing erythroblasts. Normally, 40 to 60% of developing erythroblastsѕcalled sideroblasts will have visible ferritin granules in their cytoplasm. This represents iron in excess of that needed for hemoglobin synthesis. In states in which release of iron from storage sites is blocked, RE iron will be detectable, and there will be few or no sideroblasts. In the myelodysplastic syndromes, mitochondrial dysfunction occurs, and accumulation of iron in mitochondria appears in a necklace fashion around the nucleus of the erythroblast. Such cells are referred to as ringed sideroblasts.

 

Fig. 20. Bone marrow aspirate showing erythroid hyperplasia and many binucleated erythroid precursors.

 

Serum Levels of Transferrin Receptor Protein. Because erythroid cells have the highest numbers of transferrin receptors on their surface of any cell in the body, and because transferrin receptor protein (TRP) is released by cells into the circulation, serum levels of TRP reflect the total erythroid marrow mass. Another condition in which TRP levels are elevated is absolute iron deficiency. Normal values are 4 to 9 ug/L determined by immunoassay. This laboratory test is becoming increasingly available and has been proposed to measure the serial expansion of the erythroid marrow in response to recombinant erythropoietin therapy.

 

Fig. 21. Microcytic anemia

 

Fig. 22. Peripheral smear showing classic spherocytes with loss of central pallor in the erythrocytes.

 

 

Fig. 23. Erythrocytes in severe iron deficiency.The large area of central pallor (anulocytes) is typical. The erythrocytes are flat, small, and appear pale

 

Fig. 24. Group of bone marrow erythroblasts in iron deficiency. The basophilic cytoplasm contrasts with the relatively mature nuclei (nuclear-cytoplasmic dissociation)

 

 

 

 

Fig. 25. In severe iron deficiency, even the cytoplasm of some mature erythroblasts is still basophilic and has indistinct margins

 

 

Fig. 26. Iron stain reveals absence of iron stores in bone marrow fragments due to severe iron deficiency

 

 

TREATMENT

 

Fig. 27. Iron metabolism

 

The severity and cause of iron deficiency anemia will determine the appropriate approach to treatment. As an example, symptomatic elderly patients with severe iron deficiency anemia and cardiovascular instability may require red cell transfusions. Younger individuals who have compensated for their anemia can be treated more conservatively with iron replacement. The foremost issue for the latter patient is the precise identification of the cause of the iron deficiency.

For the majority of cases of iron deficiency (pregnant women, growing children and adolescents, patients with infrequent episodes of bleeding, and those with inadequate dietary intake of iron), oral iron therapy will suffice. For patients with unusual blood loss or malabsorption, specific diagnostic tests and appropriate therapy take priority. Once the diagnosis of iron deficiency anemia and its cause is made, and a therapeutic approach is charted, there are three major approaches.

Red Cell Transfusion Transfusion therapy is reserved for those individuals who have symptoms of anemia, cardiovascular instability, and continued and excessive blood loss from whatever source, and those who require immediate intervention. The management of these patients is less related to the iron deficiency than it is to the consequences of the severe anemia. Not only do transfusions correct the anemia acutely, but the transfused red cells provide a source of iron for reutilization, assuming they are not lost through continued bleeding. Transfusion therapy will stabilize the patient while other options are reviewed.

Oral Iron Therapy In the patient with established iron deficiency anemia who is asymptomatic, treatment with oral iron is usually adequate. Multiple preparations are available ranging from simple iron salts to complex iron compounds designed for sustained release throughout the small intestine (Table 1). While the various preparations contain different amounts of iron, they are generally all absorbed well and are effective in treatment. Some come with other compounds designed to enhance iron absorption, such as citric acid. It is not clear whether the benefits of such compounds justify their costs. Typically, for iron replacement therapy up to 300 mg of elemental iron per day is given, usually as three or four iron tablets (each containing 50 to 65 mg elemental iron) given over the course of the day. Ideally, oral iron preparations should be taken on an empty stomach, since foods may inhibit iron absorption. Some patients with gastric disease or prior gastric surgery require special treatment with iron solutions, since the retention capacity of the stomach may be reduced. The retention capacity is necessary for dissolving the shell of the iron tablet before the release of iron. A dose of 200 to 300 mg of elemental iron per day should result in the absorption of up to 50 mg of iron per day. This supports a red cell production level of two to three times normal in an individual with a normally functioning marrow and appropriate erythropoietin stimulus.

Table 1. Contents of iron in some widely spread preparations:

 

Of the complications of oral iron therapy, gastrointestinal distress is the most prominent and is seen in 15 to 20% of patients. For these patients, abdominal pain, nausea, vomiting, or constipation often lead to noncompliance. Although small doses of iron or iron preparations with delayed release may help somewhat, the gastrointestinal side effects are a major impediment to the effective treatment of a number of patients.

The response to iron therapy varies, depending upon the erythropoietin stimulus and the rate of absorption. Typically, the reticulocyte count should begin to increase within 4 to 7 days after initiation of therapy and peak at 11/2 weeks. The absence of a response may be due to poor adsorption, noncompliance (which is common), or a confounding diagnosis. If iron deficiency persists, it may be necessary to switch to parenteral iron therapy.

 

Fig. 28. In the presence of some anemias, the body increases production of red blood cells (RBCs), and sends these cells into the bloodstream before they are mature. These slightly immature cells are called reticulocytes, and are characterized by a network of filaments and granules. Reticulocytes normally make up 1% of the total RBC count, but may exceed levels of 4% when compensating for anemia.

 

Parenteral Iron Therapy  Intramuscular or intravenous iron can be given to patients who are unable to tolerate oral iron, whose needs are relatively acute, or who need iron on an ongoing basis, usually due to persistent gastrointestinal blood loss. Currently, the intravenous route is used routinely. Parenteral iron use has been rising rapidly in the last several years with the recognition that recombinant erythropoietin therapy induces a large demand for ironѕa demand that frequently cannot be met through the physiologic release of iron from RE sources. Concern has been raised about the safety of parenteral iron-particularly iron dextran. The serious adverse reaction rate to intravenous iron dextran is 0.7%. Fortunately, newer iron complexes are becoming available in the United States that are likely to have an even lower rate of adverse effects. The most recently approved preparation is intravenous iron gluconate (Ferrlecit).

 

5. Megaloblastic anemia.

5.1.  Bone marrow.

5.2.  Criteria for cobalamin deficiency anemia.

5.3.  Criteria for folic acid deficiency anemia.

5.4.  Differential diagnosis of the megaloblastic anemias.

5.5. Treatment of the megaloblastic anemias.

The megaloblastic anemias are disorders caused by impaired DNA synthesis. Cells primarily affected are those having relatively rapid turnover, especially hematopoietic precursors and gastrointestinal epithelial cells. Cell division is sluggish, but cytoplasmic development progresses normally, so megaloblastic cells tend to be large, with an increased ratio of RNA to DNA. Megaloblastic erythroid progenitors tend to be destroyed in the marrow. Thus, marrow cellularity is often increased but production of red blood cells (RBC) is decreased, an abnormality termed ineffective erythropoiesis.

Most megaloblastic anemias are due to a deficiency of cobalamin (vitamin B12) and/or folic acid.

 

CLASSIFICATION OF MEGALOBLASTIC ANEMIAS. CAUSES

 

Megaloblastic anemias are characterized by ineffective erythropoiesis. In a severely megaloblastic patient, as many as 90% of the RBC precursors may be destroyed before they are released into the bloodstream, compared with 10 to 15% iormal individuals. Enhanced intramedullary destruction of erythroblasts results in an increase in unconjugated bilirubin and lactic acid dehydrogenase (isoenzyme 1) in plasma. Abnormalities in iron kinetics also attest to the presence of ineffective erythropoiesis, with increased iron turnover but low incorporation of labeled iron into circulating RBCs.

In evaluating a patient with megaloblastic anemia, it is important to determine whether there is a specific vitamin deficiency by measuring serum cobalamin and folate levels. The normal range of cobalamin in serum is 200 to 900 pg/mL; values <100 pg/mL indicate clinically significant deficiency. Measurements of cobalamin bound to TC II would be a more physiologic measure of cobalamin status, but such assays are not yet routinely available. The normal serum concentration of folic acid ranges from 6 to 20 ng/mL; values Ј4 ng/mL are generally considered to be diagnostic of folate deficiency. Unlike serum cobalamin, serum folate levels may reflect recent alterations in dietary intake. Measurement of RBC folate level provides useful information because it is not subject to short-term fluctuations in folate intake and is better than serum folate as an index of folate stores.

 

Fig. 29. This image shows a large PMN with multiple discretely-identifiable nuclear lobes, usually seen in megaloblastic anemias. Normal PMN’s have less than or equal to 5 lobes.

 

COBALAMIN DEFICIENCY

The clinical features of cobalamin deficiency involve the blood, the gastrointestinal tract, and the nervous system.

The hematologic manifestations are almost entirely the result of anemia, although very rarely purpura may appear, due to thrombocytopenia. Symptoms of anemia may include weakness, light-headedness, vertigo, and tinnitus, as well as palpitations, angina, and the symptoms of congestive failure. On physical examination, the patient with florid cobalamin deficiency is pale, with slightly icteric skin and eyes. Elevated bilirubin levels are related to high erythroid cell turnover in the marrow. The pulse is rapid, and the heart may be enlarged; auscultation will usually reveal a systolic flow murmur.

Bone marrow morphology is characteristically abnormal. Marked erythroid hyperplasia is present as a response to defective red blood cell production (ineffective erythropoiesis). Megaloblastic changes in the erythroid series include abnormally large cell size and asynchronous maturation of the nucleus and cytoplasm – ie, cytoplasmic maturation continues while impaired DNA synthesis causes retarded nuclear development. In the myeloid series, giant metamyelocytes are characteristically seen.

The gastrointestinal manifestations reflect the effect of cobalamin deficiency on the rapidly proliferating gastrointestinal epithelium. The patient sometimes complains of a sore tongue, which on inspection will be smooth and beefy red. Anorexia with moderate weight loss may also be evident, possibly accompanied by diarrhea and other gastrointestinal symptoms. These latter manifestations may be caused in part by megaloblastosis of the small intestinal epithelium, which results in malabsorption.

The neurologic manifestations often fail to remit fully on treatment. They begin pathologically with demyelination, followed by axonal degeneration and eventual neuronal death; the final stage, of course, is irreversible. Sites of involvement include peripheral nerves; the spinal cord, where the posterior and lateral columns undergo demyelination; and the cerebrum itself. Signs and symptoms include numbness and paresthesia in the extremities (the earliest neurologic manifestations), weakness, and ataxia. There may be sphincter disturbances. Reflexes may be diminished or increased. The Romberg and Babinski signs may be positive, and position and vibration senses are usually diminished. Disturbances of mentation will vary from mild irritability and forgetfulness to severe dementia or frank psychosis. It should be emphasized that neurologic disease may occur in a patient with a normal hematocrit and normal RBC indexes. Although it has many benefits, folate supplementation of food may increase the likelihood of neurologic presentations of cobalamin deficiency.

In the classic patient, in whom hematologic problems predominate, the blood and bone marrow show characteristic megaloblastic changes. The anemia may be very severeѕhematocrits of 15 to 20 are not infrequent–but is surprisingly well tolerated by the patient because it develops so slowly.

 

Fig. 30. This picture shows large, dense, oversized, red blood cells (RBCs) that are seen in megaloblastic anemia. Megaloblastic anemia can occur when there is a deficiency of vitamin B-12.

 

Pernicious Anemia  Pernicious anemia, considered the most common cause of cobalamin deficiency, is caused by the absence of IF, from either atrophy of the gastric mucosa or autoimmune destruction of parietal cells. It is most frequently seen in individuals of northern European descent and African Americans and is much less common in southern Europeans and Asians. Men and women are equally affected. It is a disease of the elderly, the average patient presenting near age 60; it is rare under age 30, although typical pernicious anemia can be seen in children under age 10 (juvenile pernicious anemia). Inherited conditions in which a histologically normal stomach secretes either an abnormal IF or none at all will induce cobalamin deficiency in infancy or early childhood.

The incidence of pernicious anemia is substantially increased in patients with other diseases thought to be of immunologic origin, including Graves’ disease, myxedema, thyroiditis, idiopathic adrenocortical insufficiency, vitiligo, and hypoparathyroidism. Patients with pernicious anemia also have abnormal circulating antibodies related to their disease: 90% have antiparietal cell antibody, which is directed against the H+,K+-ATPase, while 60% have anti-IF antibody. Antiparietal cell antibody is also found in 50% of patients with gastric atrophy without pernicious anemia, as well as in 10 to 15% of an unselected patient population, but anti-IF antibody is usually absent from these patients. Relatives of patients with pernicious anemia have an increased incidence of the disease, and even clinically unaffected relatives may have anti-IF antibody in their serum. Finally, treatment with glucocorticoids may reverse the disease.

 

 

Fig. 31. Peripheral smear of blood in a patient with pernicious anemia. Macrocytes are observed and some of the red blood cells show ovalocytosis. A 6-lobed polymorphonuclear leucocyte is present.

  

The destruction of parietal cells in pernicious anemia is thought to be mediated by cytotoxic T cells. Pernicious anemia is unusually common in patients with agammaglobulinemia, suggesting that the cellular immune system plays a role in its pathogenesis. In contrast, Helicobacter pylori does not cause parietal cell destruction in pernicious anemia.

The most characteristic finding in pernicious anemia is gastric atrophy affecting the acid- and pepsin-secreting portion of the stomach; the antrum is spared. Other pathologic changes are secondary to the deficiency of cobalamin; these include megaloblastic alterations in the gastric and intestinal epithelium and the neurologic changes described above. The abnormalities in the gastric epithelium appear as cellular atypia in gastric cytology specimens, a finding that must be carefully distinguished from the cytologic abnormalities seen in gastric malignancy.

The clinical manifestations are primarily those of cobalamin deficiency, as described above. The disease is of insidious onset and progresses slowly.

Through appropriate replacement therapy, patients with pernicious anemia should experience complete and lifelong correction of all abnormalities that are due to cobalamin deficiency, except to the extent that irreversible changes in the nervous system may have occurred before treatment. These patients, however, are unusually subject to gastric polyps and have about twice the normal incidence of cancer of the stomach. Thus, patients should be followed with frequent stool guaiac examinations and endoscopy when indicated.

Postgastrectomy  Following total gastrectomy or extensive damage to gastric mucosa as, for example, by ingestion of corrosive agents, megaloblastic anemia will develop because the source of IF has been removed. In all such patients, the absorption of orally administered cobalamin is impaired. Megaloblastic anemia may also follow partial gastrectomy, but the incidence is lower than after total gastrectomy. The cause of cobalamin deficiency after partial gastrectomy is not clear; defective release of cobalamin from food and intestinal overgrowth of bacteria have been suggested, but response to antibiotics is not common.

Intestinal Organisms  Megaloblastic anemia may occur with intestinal stasis due to anatomic lesions (strictures, diverticula, anastomoses, “blind loops“) or pseudoobstruction (diabetes mellitus, scleroderma, amyloid). This anemia is caused by colonization of the small intestine by large masses of bacteria that consume intestinal cobalamin before absorption. Steatorrhea may also be seen under these circumstances because bile salt metabolism is disturbed when the intestine is heavily colonized with bacteria. Hematologic responses have been observed after administration of oral antibiotics such as tetracycline and ampicillin. Megaloblastic anemia is seen in persons harboring the fish tapeworm, D. latum, due to competition by the worm for cobalamin. Destruction of the worm eliminates the problem.

Ileal Abnormalities  Cobalamin deficiency is common in tropical sprue, while it is an unusual complication of nontropical sprue. Virtually any disorder that compromises the absorptive capacity of the distal ileum can result in cobalamin deficiency. Specific entities include regional enteritis, Whipple’s disease, and tuberculosis. Segmental involvement of the distal ileum by disease can cause megaloblastic anemia without any other manifestations of intestinal malabsorption such as steatorrhea. Cobalamin malabsorption is also seen after ileal resection. The Zollinger-Ellison syndrome (intense gastric hyperacidity due to a gastrin-secreting tumor) may cause cobalamin malabsorption by acidifying the small intestine, retarding the transfer of the vitamin from R binder to IF and impairing the binding of the cobalamin-IF complex to the ileal receptors. Chronic pancreatitis may also cause cobalamin malabsorption by impairing the transfer of the vitamin from R binder to IF. This abnormality can be detected by tests of cobalamin absorption, but it is invariably mild and never causes clinical cobalamin deficiency. Finally, there is a rare congenital disorder, Imerslund-Grasbeck disease, in which a selective defect in cobalamin absorption is accompanied by proteinuria. Affected individuals have a mutation in cubulin, a receptor that mediates intestinal absorption of the cobalamin-IF complex.

 

Fig.32. Peripheral smear showing ovalocytes, macrocytes, and a hypersegmented polymorphonuclear leukocyte

 

FOLIC ACID DEFICIENCY

Patients with folic acid deficiency are more often malnourished than those with cobalamin deficiency. The gastrointestinal manifestations are similar to but may be more widespread and more severe than those of pernicious anemia. Diarrhea is often present, and cheilosis and glossitis are also encountered. However, in contrast to cobalamin deficiency, neurologic abnormalities do not occur.

The hematologic manifestations of folic acid deficiency are the same as those of cobalamin deficiency. Folic acid deficiency can generally be attributed to one or more of the following factors: inadequate intake, increased demand, or malabsorption.

Inadequate Intake Alcoholics may become folate deficient because their main source of caloric intake is alcoholic beverages. Distilled spirits are virtually devoid of folic acid, while beer and wine do not contain enough of the vitamin to satisfy the daily requirement. In addition, alcohol may interfere with folate metabolism. Narcotic addicts are also prone to become folate deficient because of malnutrition. Many indigent and elderly individuals who subsist primarily on canned foods or “tea and toast” and occasional teenagers whose diet consists of “junk food” develop folate deficiency. Food folate supplementation has made folate deficiency very rare.

Increased Demand Tissues with a relatively high rate of cell division such as the bone marrow or gut mucosa have a large requirement for folate. Therefore, patients with chronic hemolytic anemias or other causes of very active erythropoiesis may become deficient. Pregnant women formerly were at risk to become deficient in folic acid because of the high demand of the developing fetus. Deficiency in the first weeks of pregnancy can cause neural tube defects iewborns. Often the pregnancy was not detected until the defect had developed; thus, provision of folate supplementation to women after they learned they were pregnant was ineffective. However, folate food supplementation has decreased neural tube defects by more than 50%. Folate deficiency may also occur during the growth spurts of infancy and adolescence. Patients on chronic hemodialysis may require supplementary folate to replace that lost in the dialysate.

Malabsorption  Folic acid deficiency is a common accompaniment of tropical sprue. Both the gastrointestinal symptoms and malabsorption are improved by the administration of either folic acid or antibiotics by mouth. Patients with nontropical sprue (gluten-sensitive enteropathy) may also develop significant folic acid deficiency that parallels other parameters of malabsorption. Similarly, folate deficiency in alcoholics may be due in part to malabsorption. In addition, other primary small-bowel disorders are sometimes associated with folate deficiency.

 

Fig. 33. Histologically, the megaloblastosis caused by folic acid deficiency cannot be differentiated from that observed with vitamin B-12 deficiency.

 

DIAGNOSIS

The finding of significant macrocytosis [mean corpuscular volume (MCV) > 100 fL] suggests the presence of a megaloblastic anemia. Other causes of macrocytosis include hemolysis, liver disease, alcoholism, hypothyroidism, and aplastic anemia. If the macrocytosis is marked (MCV > 110 fL), the patient is much more likely to have a megaloblastic anemia. Macrocytosis is less marked with concurrent iron deficiency or thalassemia. The reticulocyte count is low, and the leukocyte and platelet count may also be decreased, particularly in severely anemic patients. The blood smear demonstrates marked anisocytosis and poikilocytosis, together with macroovalocytes, which are large, oval, fully hemoglobinized erythrocytes typical of megaloblastic anemias. There is some basophilic stippling, and an occasional nucleated RBC may be seen. In the white blood cell series, the neutrophils show hypersegmentation of the nucleus. This is such a characteristic finding that a single cell with a nucleus of six lobes or more should raise the immediate suspicion of a megaloblastic anemia. A rare myelocyte may also be seen. Bizarre, misshapen platelets are also observed. The reticulocyte index is low. The bone marrow is hypercellular with a decreased myeloid/erythroid ratio and abundant stainable iron. RBC precursors are abnormally large and have nuclei that appear much less mature than would be expected from the development of the cytoplasm (nuclear-cytoplasmic asynchrony). The nuclear chromatin is more dispersed than expected, and it condenses in a peculiar fenestrated pattern that is very characteristic of megaloblastic erythropoiesis. Abnormal mitoses may be seen. Granulocyte precursors are also affected, many being larger thaormal, including giant bands and metamyelocytes. Megakaryocytes are decreased and show abnormal morphology.

Megaloblastic anemias are characterized by ineffective erythropoiesis. In a severely megaloblastic patient, as many as 90% of the RBC precursors may be destroyed before they are released into the bloodstream, compared with 10 to 15% iormal individuals. Enhanced intramedullary destruction of erythroblasts results in an increase in unconjugated bilirubin and lactic acid dehydrogenase (isoenzyme 1) in plasma. Abnormalities in iron kinetics also attest to the presence of ineffective erythropoiesis, with increased iron turnover but low incorporation of labeled iron into circulating RBCs.

In evaluating a patient with megaloblastic anemia, it is important to determine whether there is a specific vitamin deficiency by measuring serum cobalamin and folate levels. The normal range of cobalamin in serum is 200 to 900 pg/mL; values <100 pg/mL indicate clinically significant deficiency. Measurements of cobalamin bound to TC II would be a more physiologic measure of cobalamin status, but such assays are not yet routinely available. The normal serum concentration of folic acid ranges from 6 to 20 ng/mL; values Ј4 ng/mL are generally considered to be diagnostic of folate deficiency. Unlike serum cobalamin, serum folate levels may reflect recent alterations in dietary intake. Measurement of RBC folate level provides useful information because it is not subject to short-term fluctuations in folate intake and is better than serum folate as an index of folate stores.

Once cobalamin deficiency has been established, its pathogenesis can be delineated by means of a Schilling test. A patient is given radioactive cobalamin by mouth, followed shortly thereafter by an intramuscular injection of unlabeled cobalamin. The proportion of the administered radioactivity excreted in the urine during the next 24 h provides an accurate measure of absorption of cobalamin, assuming that a complete urine sample has been collected. Because cobalamin deficiency is almost always due to malabsorption, this first stage of the Schilling test should be abnormal (i.e., small amounts of radioactivity in the urine). The patient is then given labeled cobalamin bound to IF. Absorption of the vitamin will now approach normal if the patient has pernicious anemia or some other type of IF deficiency. If cobalamin absorption is still decreased, the patient may have bacterial overgrowth (blind loop syndrome) or ileal disease (including an ileal absorptive defect secondary to the cobalamin deficiency itself). Cobalamin malabsorption due to bacterial overgrowth can frequently be corrected by the administration of antibiotics. The Schilling test can provide equally reliable information after the patient has had adequate therapy with parenteral cobalamin.

A normal Schilling test in a patient with documented cobalamin deficiency may indicate poor absorption of the vitamin when mixed with food. This can be established by repeating the Schilling test with radioactive cobalamin scrambled with an egg.

Serum methylmalonic acid and homocysteine levels are also useful in the diagnosis of megaloblastic anemias. Both are elevated in cobalamin deficiency, while elevated levels of homocysteine but not methylmalonic acid are seen in folate deficiency. These tests measure tissue vitamin stores and may demonstrate a deficiency even when the more traditional but less reliable folate and cobalamin levels are borderline or eveormal. Patients (particularly older patients) without anemia and with normal serum cobalamin levels but elevated levels of serum methylmalonic acid may develop neuropsychiatric abnormalities. Treatment of patients with this “subtle” cobalamin deficiency will usually prevent further deterioration and may result in improvement.

 

 

Fig. 34. Bone marrow aspirate from a patient with untreated pernicious anemia. Megaloblastic maturation of erythroid precursors is shown. Two megaloblasts occupy the center of the slide with a megaloblastic normoblast above.

 

TREATMENT

Cobalamin Deficiency  Apart from specific therapy related to the underlying disorder (e.g., antibiotics for intestinal overgrowth with bacteria), the mainstay of treatment for cobalamin deficiency is replacement therapy. Because the defect is nearly always malabsorption, patients are generally given parenteral treatment, specifically in the form of intramuscular cyanocobalamin. Parenteral treatment begins with 1000 ug cobalamin per week for 8 weeks, followed by 1000 ug cyanocobalamin intramuscularly every month for the rest of the patient’s life. However, cobalamin deficiency can also be managed very effectively by oral replacement therapy with 2 mg crystalline B12 per day.

The response to treatment is gratifying. Shortly after treatment is begun, and several days before a hematologic response is evident in the peripheral blood, the patient will experience an increase in strength and an improved sense of well-being. Marrow morphology begins to revert toward normal within a few hours after treatment is initiated. Reticulocytosis begins 4 to 5 days after therapy is started and peaks at about day 7 (Fig. 35), with subsequent remission of the anemia over the next several weeks. If a reticulocytosis does not occur, or if it is less brisk than expected from the level of the hematocrit, a search should be made for other factors contributing to the anemia (e.g., infection, coexisting iron and/or folate deficiency, or hypothyroidism). Hypokalemia and salt retention may occur early in the course of therapy. Thrombocytosis may also be seen.

In most cases, replacement therapy is all that is needed for the treatment of cobalamin deficiency. Occasionally, however, a patient with a severe anemia will have such a precarious cardiovascular status that emergency transfusion is necessary. This must be done with great care, because such patients may develop heart failure from fluid overload. Blood must be administered slowly in the form of packed RBCs, with very close observation. A small volume of packed RBCs will frequently be enough to ameliorate the acute cardiovascular problems. If necessary, blood may be administered by exchanging patient blood (mostly plasma) for packed cells.

With lifelong treatment, patients should experience no further manifestations of cobalamin deficiency, although neurologic symptoms may not be fully corrected even by optimal therapy. The potential for late development of gastric carcinoma in pernicious anemia necessitates careful follow-up of the patient.

Folate, particularly in large doses, can correct the megaloblastic anemia of cobalamin deficiency without altering the neurologic abnormalities. The neurologic manifestations may even be aggravated by folate therapy. Cobalamin deficiency can thus be masked in patients who are taking large doses of folate. For this reason, a hematologic response to folate must never be used to rule out cobalamin deficiency in a given patient; cobalamin deficiency can be excluded only by appropriate laboratory evaluation.

In light of the high frequency of defective cobalamin absorption in older people and the possible increased risk that overt cobalamin deficiency will present with neurologic rather than hematologic symptoms (because of folate food fortification), some experts have recommended the use of 0.1 mg oral crystalline cobalamin prophylaxis daily in people over age 65 years.

 

 

Fig. 35. Response to therapy with cobalamin (Cbl) in a previously untreated patient with pernicious anemia. A reticulocytosis occurs within 5 days after an injection of 1000 mcg of Cbl. This lasts for about 2 weeks after injection. The hemoglobin (Hgb) concentration increases at a slower rate because many of the reticulocytes are abnormal and do not survive as mature erythrocytes.

 

Folate Deficiency As for cobalamin deficiency, folate deficiency is treated by replacement therapy. The usual dose of folate is 1 mg/d, by mouth, but higher doses (up to 5 mg/d) may be required for folate deficiency due to malabsorption. Parenteral folate is rarely necessary. The hematologic response is similar to that seen after replacement therapy for cobalamin deficiency, i.e., a brisk reticulocytosis after about 4 days, followed by correction of the anemia over the next 1 to 2 months. The duration of therapy depends on the basis of the deficiency state. Patients with a continuously increased requirement (such as patients with hemolytic anemia) or those with malabsorption or chronic malnutrition should continue to receive oral folic acid indefinitely. In addition, the patient should be encouraged to maintain an optimal diet containing adequate amounts of folate.

Other Causes of Megaloblastic Anemia  Megaloblastic anemia due to drugs can be treated, if necessary, by reducing the dose of the drug or eliminating it altogether. The effects of folate antagonists that inhibit dihydrofolate reductase can be counteracted by folinic acid [5-formyl tetrahydrofolate (THF)] in a dose of 100 to 200 mg/d, which circumvents the block in folate metabolism by providing a form of folate that can be converted to 5,10-methylene THF. For the megaloblastic forms of sideroblastic anemia, pyridoxine in pharmacologic doses (as high as 300 mg/d) should be tried. If this fails, pyridoxal phosphate may work, presumably in part by promoting the conversion of THF to 5,10-methylene THF. Simple supportive measures are all that appear to be in order for treatment of refractory megaloblastic anemia. Acute erythroleukemia (di Guglielmo’s disease) is usually treated like other types of acute myeloid leukemia.

  

6.  Hemolytic anemias.

6.1. Hereditary hemolytic anemias.

6.2. Classification of hemolysis.

6.2.1. Criteria for spherocytosis.

The loss of red cells either through hemorrhage or, less commonly, through premature destruction of the red cells (hemolysis) may cause anemia. Hemolysis or blood loss normally leads to an increase in red cell production, which is clinically manifested by an increase in reticulocytes.

 

HEMOLYTIC ANEMIAS

Red blood cells (RBC) normally survive 90 to 120 days in the circulation. The life span of RBC may be shortened in a number of disorders, often resulting in anemia if the bone marrow is not able to replenish adequately the prematurely destroyed RBC. The disorders associated with hemolytic anemias are generally identified by the abnormality that brings about the premature destruction of the RBC.

In all patients with hemolytic anemia, a careful history and physical examination provide important clues to the diagnosis. The patient may complain of fatigue and other symptoms of anemia. Less commonly, jaundice and even red-brown urine (hemoglobinuria) are reported. A complete drug and toxin exposure history and the family history often provide crucial information. The physical examination may show jaundice of skin and mucosae. Splenomegaly is encountered in a variety of hemolytic anemias. A wide array of other historic and physical findings is associated with specific hemolytic anemias (see below).

 

Fig. 36. Polychromasia.

 

Laboratory tests may be used initially to demonstrate the presence of hemolysis and define its cause. An elevated reticulocyte count in the patient with anemia is the most useful indicator of hemolysis, reflecting erythroid hyperplasia of the bone marrow; biopsy of the bone marrow is often unnecessary. Reticulocytes are also elevated in patients with active blood loss, those with myelophthisis, and those who are recovering from suppression of erythropoiesis. While the findings on the peripheral blood smear alone are rarely pathognomonic, they may provide important clues to the presence of hemolysis and to diagnosis.

 

Fig. 37. Spherocytes. One arrow points to a spherocyte; the other, to a normal RBC with a central pallor.

 

RBC may be prematurely removed from the circulation by macrophages, particularly those of the spleen and liver (extravascular lysis), or, less commonly, by disruption of their membranes during their circulation (intravascular hemolysis). Both mechanisms result in increased heme catabolism and enhanced formation of unconjugated bilirubin, which is normally conjugated by the liver and excreted. The plasma level of unconjugated bilirubin may be high enough to produce readily apparent jaundice (detectable usually when serum bilirubin is >34 umol/L or 2 mg/dL). The unconjugated (indirect) bilirubin level can be further elevated by a commonly encountered defect in conjugation of bilirubin (Gilbert’s syndrome). In patients with hemolysis, the level of unconjugated bilirubiever exceeds 70 to 85 umol/L (4 to 5 mg/dL), unless liver function is impaired.

In the absence of tissue damage in other organs, serum enzyme levels can be useful in the diagnosis and monitoring of patients with hemolysis. Lactate dehydrogenase (LDH), particularly LDH-2, is elevated by accelerated RBC destruction. Serum AST (SGOT) may be somewhat elevated, whereas ALT (SGPT) is not.

Haptoglobin is an a globulin that is present in high concentration (~1.0 g/L) in the plasma (and serum). It binds specifically and tightly to the globin in hemoglobin. The hemoglobin-haptoglobin complex is cleared within minutes by the mononuclear phagocyte system. Thus patients with significant hemolysis, either intravascular or extravascular, have low or absent levels of serum haptoglobin. The fact that haptoglobin synthesis is decreased in patients with hepatocellular disease and increased in inflammatory states must be considered in the interpretation of serum haptoglobin.

 

Fig. 38. Schistocytes (thrombotic thrombocytopenic purpura).

 

 

Intravascular hemolysis (which is uncommon) results in the release of hemoglobin into the plasma. In these cases, plasma hemoglobin is increased in proportion to the degree of hemolysis. Plasma hemoglobin may be falsely elevated due to lysis of RBC in vitro. If the haptoglobin-binding capacity of the plasma is exceeded, free hemoglobin passes through renal glomeruli. This filtered hemoglobin is reabsorbed by the proximal tubule, where it is catabolized in situ, and the heme iron is incorporated into storage proteins (ferritin and hemosiderin). The presence of hemosiderin in the urine, detected by staining the sediment with Prussian blue, indicates that a significant amount of circulating free hemoglobin has been filtered by the kidneys. Hemosiderin appears 3 to 4 days after the onset of hemoglobinuria and may persist for weeks after its cessation. When the absorptive capacity of the tubular cells is exceeded, hemoglobinuria ensues. Hemoglobinuria indicates severe intravascular hemolysis. Hemoglobinuria must be distinguished from hematuria (in which case RBC are seen on urine examination) and from myoglobin due to rhabdomyolysis; in all three cases, the urine is positive with the benzidine reaction, commonly used in analysis of urine. The distinction between hemoglobinuria and myoglobinuria can best be made by specific tests that exploit immunologic differences or differences in solubility. After centrifugation of an anticoagulated blood specimen, the plasma of patients with hemoglobinuria has a reddish-brown color, whereas that of patients with myoglobinuria is normal in color. Because of its higher molecular weight, hemoglobin has lower glomerular permeability than myoglobin and is less rapidly cleared by the kidneys.

 

CLASSIFICATION

The hemolytic anemias can be grouped in three different ways, shown in Table 108-3. The cause of accelerated RBC destruction can be regarded as

1) a molecular defect (hemoglobinopathy or enzymopathy) inside the red cell,

2) an abnormality in membrane structure and function,

3) an environmental factor such as mechanical trauma or an autoantibody.

 

 

Classification of haemolytic anemia

In intracorpuscular types of hemolysis, the patient’s RBC have an abnormally short life span in a normal recipient (with a compatible blood type), while compatible normal RBC survive normally in the patient. The opposite is true in extracorpuscular types of hemolysis. Finally, hemolytic disorders can be classified as either inherited or acquired.

In contrast to anemias associated with an inappropriately low reticulocyte production index, blood loss or hemolysis is associated with red cell production indices of >2.5 times normal. The stimulated erythropoiesis is reflected in the blood smear by the appearance of increased numbers of polychromatophilic macrocytes. A marrow examination is rarely indicated if the reticulocyte production index is increased appropriately. The red cell indices are typically normocytic or slightly macrocytic, reflecting the increased number of reticulocytes. Acute blood loss is not associated with an increased reticulocyte production index because of the time required to increase EPO production and, subsequently, marrow proliferation. Subacute blood loss may be associated with modest reticulocytosis because iron is lost along with the red cells. Anemia from chronic blood loss more often presents as iron deficiency than with the picture of increased red cell production.

Hemolytic disease, while dramatic, is among the least common forms of anemia. The ability to sustain a high reticulocyte production index reflects the ability of the erythroid marrow to compensate for hemolysis and the efficient recycling of iron from the destroyed red cells to support new hemoglobin synthesis. The level of response will depend on the severity of the anemia and the nature of the underlying disease process.

Hemolytic anemias present in different ways. Some appear suddenly as an acute, self-limited episode of intravascular or extravascular hemolysis, a presentation pattern often seen in patients with autoimmune hemolysis or with inherited defects of the Embden-Myerhof pathway or the glutathione reductase pathway. Patients with inherited disorders of the hemoglobin molecule or red cell membrane generally have a lifelong clinical history typical of the disease process. Those with chronic hemolytic disease, such as hereditary spherocytosis, may actually present not with anemia but with a complication stemming from the prolonged increase in red cell destruction such as aplastic crisis, symptomatic bilirubin gallstones, or splenomegaly.

 

Hereditary spherocytosis  This condition is characterized by spherical RBC due to a molecular defect in one of the proteins in the cytoskeleton of the RBC membrane, leading to a loss of membrane and hence decreased ratio of surface area to volume and consequently spherocytosis. This disorder usually has an autosomal dominant inheritance pattern and an incidence of approximately 1:1000 to 1:4500. In ~20% of patients, the absence of hematologic abnormalities in family members suggests either autosomal recessive inheritance or a spontaneous mutation. The disorder is sometimes clinically apparent in early infancy but often escapes detection until adult life.

 

 

Fig. 39. Peripheral smear showing classic spherocytes with loss of central pallor in the erythrocytes.

  

CLINICAL MANIFESTATIONS  The major clinical features of hereditary spherocytosis are anemia, splenomegaly, and jaundice. The prominence of jaundice accounts for the disorder’s prior designation as “congenital hemolytic jaundice” and is due to an increased concentration of unconjugated (indirect-reacting) bilirubin in plasma. Jaundice may be intermittent and tends to be less pronounced in early childhood. Because of the increased bile pigment production, pigmented gallstones are common, even in childhood. Compensatory erythroid hyperplasia of the bone marrow occurs, with the extension of red marrow into the midshafts of long bones and occasionally with extramedullary erythropoiesis, at times leading to the formation of paravertebral masses visible on chest x-ray. Because the bone marrow’s capacity to increase erythropoiesis by six- to eightfold exceeds the usual rate of hemolysis, anemia is usually mild or moderate and may even be absent in an otherwise healthy individual. Compensation may be temporarily interrupted by episodes of relative erythroid hypoplasia precipitated by infections, particularly parvovirus, trauma, surgery, and pregnancy. Splenomegaly is very common. The hemolytic rate may increase transiently during systemic infections, which induce further splenic enlargement. Chronic leg ulcers, similar to those observed in sickle cell anemia, occur occasionally.

The characteristic erythrocyte abnormality is the spherocyte. The mean corpuscular volume (MCV) is usually normal or slightly decreased, and the mean corpuscular hemoglobin concentration (MCHC) is increased to 350 to 400 g/L. Spheroidicity may be quantitatively assessed by measurement of the osmotic fragility of the RBC on exposure to hypoosmotic solutions causing a net influx of water. Because spherocytes have a decreased surface area per unit volume, they are able to take in less water and hence lyse at a higher concentration of saline thaormal cells. On microscopic examination, spherocytes are usually detected as small cells without central pallor. They will ordinarily not influence the osmotic fragility test unless they constitute more than 1 or 2% of the total cell population. The autohemolysis test, which measures the amount of spontaneous hemolysis occurring after 48 h of sterile incubation, is also useful.

 

Fig. 40. Peripheral smear that shows evidence of hereditary pyropoikilocytosis.

 

DIAGNOSIS  Hereditary spherocytosis must be distinguished primarily from the spherocytic hemolytic anemias associated with RBC antibodies. The family history of anemia and/or splenectomy is helpful, when present. The diagnosis of immune spherocytosis is usually readily established by a positive direct Coombs test (see below). Spherocytes are also seen in association with hemolysis induced by splenomegaly in patients with cirrhosis, in clostridial infections, and in certain snake envenomations (due to the action of phospholipases on the membrane). A few spherocytes are seen in the course of a wide variety of hemolytic disorders, particularly glucose-6-phosphate dehydrogenase (G6PD) deficiency.

 

Fig. 41. Heinz body (Glucose-6-Phosphate Dehydrogenase Deficiency)

 

TREATMENT

Splenectomy reliably corrects the anemia, although the RBC defect and its consequent morphology persist. The operative risk is low. RBC survival after splenectomy is normal or nearly so; if it is not, an accessory spleen or another diagnosis should be sought. Because of the potential for gallstones and for episodes of bone marrow hypoplasia or hemolytic crises, splenectomy should be performed in symptomatic individuals; cholecystectomy should not be performed without splenectomy, as intrahepatic gallstones may result. Splenectomy in children should be postponed until age 4, if possible, to minimize the risk of severe infections with gram-positive encapsulated organisms. Polyvalent pneumococcal vaccine should be administered at least 2 weeks before splenectomy. In patients with severe hemolysis, folic acid (1 mg/d) should be administered prophylactically.

 

6.2.         Acquired hemolytic anemia.

6.2.1.  Classification of the hematolytic anemias.

6.2.2.  Criteria for hemolytic anemia with antibodies.

6.2.3.  Kinds of drug-induced hemolytic anemias.

6.2.4.  Differential diagnosis of hemolytic anemias.

6.2.5.  Treatment of the hemolytic anemias.

 

ACQUIRED HEMOLYTIC ANEMIAS

In most patients with acquired hemolytic anemia, RBC are made normally but are prematurely destroyed because of damage acquired in the circulation. (The exceptions are rare disorders characterized by acquired dysplasia of the cells of the bone marrow and the production of structurally and functionally abnormal RBC.) The damage that occurs may be mediated by antibodies or toxins or may be due to abnormalities in the circulation, including an overactive mononuclear phagocyte system or traumatic lysis by natural or artificial impediments to circulation. The acquired hemolytic anemias can be classified into five categories (Table 3).

 

 

Hypersplenism  The spleen is particularly efficient in trapping and destroying RBC that have minimal defects. This unique ability of the spleen to filter mildly damaged RBC results from its unusual vascular anatomy. Almost all the blood circulating through the spleen flows rapidly from arterioles in the white pulp to sinuses in the spleen’s red pulp and then into the venous system. In contrast, a small portion of splenic blood flow (normally 1 to 2%) passes into the “marginal zone” of the lymphatic white pulp. Although the cells that occupy this zone are not phagocytic, they serve as a mechanical filter that hinders the progress of severely damaged blood cells. As RBC leave this zone and enter the red pulp, they flow into narrow cords, rich in macrophages, that end blindly but communicate with sinuses through small openings between the lining cells of the sinuses. These openings, averaging 3 um in diameter, test the ability of RBC (4.5 um in diameter) to undergo a deformation. RBC that cannot re-enter the vascular sinuses are engulfed by phagocytic cells and destroyed.

The normal spleen retains reticulocytes for 1 to 2 days but otherwise poses no threat to normal RBC until they become senescent. However, in the face of splenomegaly, increased destruction of the cells of the blood, including the RBC, may take place due to pooling of the blood in a relatively nutrient-poor environment full of phagocytic cells. When splenic sequestration causes cytopenia, hypersplenism is diagnosed. In infiltrative diseases of the spleen, substantial splenomegaly may exist with no apparent hemolysis; inflammatory and congestive splenomegaly is commonly associated with modest shortening of RBC survival time, along with more marked granulocytopenia and thrombocytopenia. Patients with cytopenia(s) sufficient to produce symptoms generally benefit from splenectomy.

Immunologic Causes of Hemolysis  Immune hemolysis in the adult is usually induced by IgG or IgM antibodies with specificity for antigens associated with the patient’s RBC (often called “autoantibodies”) (Table 3); rarely, transfused RBC may be hemolyzed by alloantibodies directed against foreign antigens on those cells.

The Coombs antiglobulin test is the major tool for diagnosing autoimmune hemolysis. This test relies on the ability of antibodies specific for immunoglobulins (especially IgG) or complement components (especially C3) to agglutinate RBC when these proteins are present on the RBC. The direct Coombs test measures the ability of anti-IgG or anti-C3 antisera to agglutinate the patient’s RBC. The presence or absence of IgG and/or C3 may help define the origin of the immune hemolytic anemia (Table 3). Rarely, neither IgG nor complement may be found on the RBC of the patient (Coombs-negative immune hemolytic anemia).

Antibodies to particular RBC antigens in the serum of the patient can be detected by reacting the serum with normal RBC bearing the antigen. IgM antibodies (usually cold-reacting) may be detected by agglutination of normal or fetal RBC. IgG antibodies may be detected by the indirect Coombs test, in which the serum of the patient is incubated with normal RBC and antibody is detected with anti-IgG, as in the direct Coombs test.

“Warm” antibodies  Antibodies that react with protein antigens are nearly always IgG and react at body temperature; occasionally, they are IgA and rarely IgM. Hemolysis due to autologous antibodies is called autoimmune hemolytic (or immunohemolytic) anemia, warm antibody type.

 

CLINICAL MANIFESTATIONS  Immunohemolytic anemia of the warm antibody type is induced by IgG antibody and occurs at all ages, but it is more common in adults, particularly women. In approximately one-fourth of patients this disorder occurs as a complication of an underlying disease affecting the immune system, especially lymphoid neoplasms; collagen vascular diseases, especially systemic lupus erythematosus (SLE); and congenital immunodeficiency diseases (Table 4). In the initial evaluation of the patient, drugs that are known to cause immunohemolytic anemia must be ruled out (see below). The presentation and course of IgG immunohemolytic anemia are quite variable. In its mildest form, the only manifestation is a positive direct Coombs test. In this instance, insufficient antibody is present on the RBC surface to permit the reticuloendothelial system to recognize the cell as abnormal.

 

 

Most symptomatic patients have a moderate to severe anemia [hemoglobin levels 60 to 100 g/L and reticulocyte counts 10 to 30% (200 to 600 ґ 103/uL)], spherocytosis, and splenomegaly.

Severe immunhemolytic anemia presents with fulminant hemolysis associated with hemoglobinemia, hemoglobinuria, and shock; this syndrome may be rapidly fatal unless aggressively treated.

The direct Coombs test is positive in 98% of patients; usually IgG is detected with or without C3. Rarely, the cells may be agglutinated by the antibody, causing difficulty in analysis by flow cytometry.

Immune thrombocytopenia also may be present (Evans’s syndrome), a disorder in which separate antibodies are directed against platelets and RBC. Occasionally, venous thrombosis occurs.

 

PATHOGENESIS

 IgG antibodies lyse RBC by two mechanisms:

(1) immune adherence of RBC to phagocytes mediated by the antibody and by complement components that become fixed to the membrane (by far the more important mechanism of destruction),

(2) complement activation.

Upon binding to Fc receptors on macrophages, the antibody-coated red cell is engulfed and destroyed. If internalization is only partial, the RBC membrane is removed, resulting in the formation of spherocytes, which are destroyed in the spleen. Complement-mediated immune adherence involves the interaction of C3b and C4b with receptors on the macrophage; while much less likely to lead to RBC lysis, this mechanism markedly increases the immune adherence due to IgG. Immune adherence, particularly that due to the IgG antibody, is also enhanced by the transit of RBC into the cords and sinuses of the spleen, which brings cells into intimate contact with phagocytic cells.

 

TREATMENT

Patients having a mild degree of hemolysis usually do not require therapy. In those with clinically significant hemolysis, initial therapy consists of glucocorticoids (e.g., prednisone, 1.0 mg/kg per day). A rise in hemoglobin is frequently noted within 3 or 4 days and occurs in most patients within 1 to 2 weeks. Prednisone is continued until the hemoglobin level has risen to normal values, and thereafter it is tapered rapidly to about 20 mg/d, then slowly over the course of several months. For chronic therapy with prednisone, alternate-day administration is preferred. More than 75% of patients achieve an initial significant and sustained reduction in hemolysis; however, in half these patients the disease recurs, either during glucocorticoid tapering or after its cessation. Glucocorticoids have two modes of action: an immediate effect due to inhibition of the clearance of IgG-coated RBC by the mononuclear phagocyte system and a later effect due to inhibition of antibody synthesis. Splenectomy is recommended for patients who cannot tolerate or fail to respond to glucocorticoid therapy.

Patients who have been refractory to glucocorticoid therapy and to splenectomy are treated with immunosuppressive drugs such as azathioprine and cyclophosphamide. A success rate of ~50% has been reported with each. Intravenous gamma globulin may cause rapid cessation of hemolysis; however, it is not nearly as effective in this disorder as in immune thrombocytopenia.

Patients with severe anemia may require blood transfusions. Because the antibody in this disease is usually a “panagglutinin,” reacting with nearly all normal donor cells, cross-matching is impossible. The goal in selecting blood for transfusion is to avoid administering RBC with antigens to which the patient may have alloantibodies. A common procedure is to adsorb the panagglutinin present in the patient’s serum with the patient’s own RBC from which antibody has been previously eluted. Serum cleared of autoantibody can then be tested for the presence of alloantibody to donor blood groups. ABO-compatible RBC matched in this fashion are administered slowly, with watchfulness for signs of an immediate-type hemolytic transfusion reaction.

 

PROGNOSIS

 In most patients, hemolysis is controlled by glucocorticoid therapy alone, by splenectomy, or by a combination. Fatalities occur among three rare subsets of patients:

 (1) those with overwhelming hemolysis who die from anemia;

(2) those whose host defenses are impaired by glucocorticoids, splenectomy, and/or immunosuppressive agents;

(3) those with major thrombotic events coincident with active hemolysis.

 

 

Paroxysmal Nocturnal Hemoglobinuria (PNH)

This hemolytic disorder is distinctive because it is an intracorpuscular defect acquired at the stem cell level.

Clinical manifestations  The three common manifestations of PNH are: hemolytic anemia, venous thrombosis, and deficient hematopoiesis. Anemia is highly variable with hematocrit values ranging from Ј20% to normal. RBC are normochromic and normocytic unless iron deficiency has occurred from chronic iron loss in the urine.

Granulocytopenia and thrombocytopenia are common and reflect deficient hematopoiesis. Clinical hemoglobinuria is intermittent in most patients and never occurs in some, but hemosiderinuria is usually present. The lack of two proteins, decay-accelerating factor (DAF, CD55) and a membrane inhibitor of reactive lysis (MIRL, CD59) (see below) make the RBC more sensitive to the lytic effect of complement.

DAF normally disrupts the enzyme complexes from either the classical (antibody-driven) pathway or the alternative pathway that activate C3 and C5; CD59 inhibits the conversion of C9 by the membrane attack complex C5b-8 to a polymeric complex capable of penetrating the membrane.

The platelets also lack these proteins, but the life span of the platelet is normal. However, the activation of complement indirectly stimulates platelet aggregation and hypercoagulability; this probably accounts for the tendency to thrombosis seen in PNH.

Venous thrombosis is a common complication of patients of European origin, affecting ~40% at one time or another; it is less common in Asian patients. It occurs primarily in intraabdominal veins (hepatic, portal, mesenteric) and results in the Budd-Chiari syndrome, congestive splenomegaly, and abdominal pain. It may occur in cerebral venous sinuses and is a common cause of death in patients with PNH. The bone marrow may appear normocellular, but in vitro marrow progenitor assays are abnormal. In about 15 to 30% of long-term survivors of aplastic anemia, PNH cells appear in the circulation; in some patients, the manifestations of PNH become dominant. Patients with PNH may have aplastic periods lasting from weeks to years. PNH may be seen in association with other stem cell disorders, including myelofibrosis, and (rarely) other myelodysplastic or myeloproliferative disorders.

 

Fig. 42. This series of containers holds urine of a patient with PNH, showing the episodic nature of the dark urine (hemoglobinuria) during intravascular hemolysis, usually occurring at night. Early morning urine is cola-colored. This may occur at different times of the day and vary from patient to patient.

 

 

Fig. 43. The Ham test (acidified serum lysis) establishes the diagnosis of paroxysmal nocturnal hemoglobinuria (PNH) demonstrating a characteristic abnormality of PNH red cells by acidified fresh normal serum. Here is a PNH patient’s red cells lysed by normal serum at room temperature (RT) and at 37°C compared to normal red cells (no hemolysis). Heated serum at 56°C inactivates complement and prevents hemolysis in PNH cells.

 

Pathogenesis  PNH is an acquired clonal disease, arising from an inactivating somatic mutation in a single abnormal stem cell of a gene on the X-chromosome (pig-A) important for the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor. This anchor is necessary for the attachment of a number of proteins to the external membrane surface, and its partial or complete absence results in the absence of those proteins; to date, about 20 proteins have been found to be missing on the blood cells of patients with PNH. The normal clone of stem cells does not completely disappear, and the proportion of cells that are abnormal varies among patients and over time in a single patient.

Diagnosis  PNH should be suspected in anyone with otherwise unexplained hemolytic anemia, especially with leukopenia and/or thrombocytopenia and with evidence of intravascular hemolysis (hemoglobinemia, hemoglobinuria, hemosiderinuria, elevated LDH). Anyone recovering from aplastic anemia should be examined at intervals for the appearance of the diagnostic cells.

The diagnosis is often delayed because:

 (1) it is not considered,

 (2) hemoglobinuria is confused with hematuria,

 (3) elevation of the LDH is attributed to liver disease,

 (4) the diagnostic tests (Ham’s test and the sucrose lysis test) are not reliable.

For many years, the diagnosis of PNH depended on the demonstration of the lysis of RBC after complement activation either by acid (Ham or acidified serum lysis test) or by reduction in ionic strength (sucrose lysis test). These tests are inferior to the analysis of GPI-linked proteins (e.g., CD59, DAF) on RBC and granulocytes by flow cytometry.

TREATMENT

Transfusion therapy is useful in PNH not only for raising the hemoglobin level but also for suppressing the marrow production of RBC during episodes of sustained hemoglobinuria. Washed RBC are the preferred source to prevent exacerbation of hemolysis. Therapy with androgens sometimes results in a rise in hemoglobin level. Glucocorticoids reduce the rate of hemolysis in moderate doses (15 to 30 mg prednisone) on alternate days.

Iron deficiency is common. Iron replacement may exacerbate hemolysis because of the formation of many new RBC, which may be sensitive to complement. This occurrence may be minimized by giving prednisone (60 mg/d) or by suppressing the bone marrow with transfusions.

Acute thrombosis in PNH, particularly the Budd-Chiari syndrome and cerebral thrombosis, should be treated with thrombolytic agents. Heparin therapy should be instituted rapidly and maintained for several days before changing to coumadin therapy. Antithymoctye globulin (total dose of 150 mg/kg over 4 to 10 days) is often of use in treating marrow hypoplasia; prednisone counteracts the immune-complex disease that results from the administration of this foreign protein.

In patients with either hypoplasia or thrombosis who have an appropriate sibling donor, marrow transplantation should be considered early in the course of the disease. The usual conditioning programs are sufficient to eradicate the aberrant clone.

 

Hemoglobinuria, Paroxysmal Cold

 

Fig. 44. Paroxysmal cold hemoglobinuria. Seen here is a Donath-Landsteiner test result showing the appearance of a negative tube (no hemolysis in the supernatant) and a positive tube (red color in the supernate, implying the presence of free hemoglobin).

 

 

 

7.              Hypo- and aplastic anemias

7.1. Bone marrow.

7.2. Criteria for diagnosis.

7.3. Criteria for stage of hypo- and aplastic anemias.

7.4. Differential diagnosis.

7.5. Treatment.

The hypoproliferative anemias associated with marrow damage include aplastic anemia, myelodysplasia (MDS), pure red cell aplasia (PRCA), and myelopthisis. Anemia in these disorders, which is normochromic, normocytic, or macrocytic and characterized by low reticulocyte count, is not a solitary or even the major finding in these diseases, which are better described as marrow failure states. In bone marrow failure, pancytopenia-anemia, leukopenia, and thrombocytopenia (sometimes in various combinations)-results from deficient hematopoiesis, as distinguished from blood count depression due to peripheral destruction of red cells (hemolytic anemias), platelets (idiopathic thrombocytopenic purpura or due to splenomegaly), and granulocytes (as in the immune leukopenias).

Hematopoietic failure syndromes are classified by dominant morphologic features of the bone marrow (Table 6).

 

  

APLASTIC ANEMIA

DEFINITION

Aplastic anemia is pancytopenia with bone marrow hypocellularity. Acquired aplastic anemia is distinguished from iatrogenic marrow aplasia, the common occurrence of marrow hypocellularity after intensive cytotoxic chemotherapy for cancer. Aplastic anemia can also be constitutional: the genetic disease Fanconi’s anemia, while frequently associated with typical physical anomalies and the development of pancytopenia early in life, can also present as marrow failure iormal-appearing adults. Acquired aplastic anemia is often stereotypical in its manifestations, with the abrupt onset of low blood counts in a previously well young adult; seronegative hepatitis or a course of an incriminated medical drug may precede the onset. The diagnosis in these instances is uncomplicated. Sometimes blood count depression is moderate or incomplete, resulting in anemia, leukopenia, and thrombocytopenia in some combination. Aplastic anemia is related to both paroxysmal nocturnal hemoglobinuria (PNH) and to MDS, and in some cases a clear distinction among these disorders may not be possible.

ETIOLOGY

The origins of aplastic anemia have been inferred from several recurring clinical associations (Table 7); unfortunately, these relationships are neither a reliable guide in an individual patient nor necessarily etiologic. In addition, while most cases of aplastic anemia are idiopathic, little other than history separates these cases from those with a presumed etiology such as a drug exposure.

 

 

Radiation  Marrow aplasia is a major acute sequela of radiation. Radiation damages DNA; tissues dependent on active mitosis are particularly susceptible. Nuclear accidents can involve not only power plant workers but also employees of hospitals, laboratories, and industry (food sterilization, metal radiography, etc.), as well as innocents exposed to stolen, misplaced, or misused sources. While the radiation dose can be approximated from the rate and degree of decline in blood counts, dosimetry by reconstruction of the exposure can help to estimate the patient’s prognosis and also to protect medical personnel from contact with radioactive tissue and excreta. MDS and leukemia, but probably not aplastic anemia, are late effects of irradiation.

Chemicals  Benzene is a notorious cause of bone marrow failure. Vast quantities of epidemiologic, clinical, and laboratory data link benzene to aplastic anemia, acute leukemia, and blood and marrow abnormalities. The occurrence of leukemia is roughly correlated with cumulative exposure, but susceptibility must also be important, as only a minority of even heavily exposed workers develop benzene myelotoxicity. The employment history is important, especially in industries where benzene is used for a secondary purpose, usually as a solvent. Benzene-related blood diseases have declined with regulation of industrial exposure. Although benzene is no longer generally available as a household solvent, exposure to its metabolites occurs in the normal diet and in the use of lead-free gasoline. The association between marrow failure and other chemicals that contain a benzene ring is much less well substantiated; these chemicals may have been contaminated with benzene in manufacture, or petroleum distillates may have been used to dissolve the product.

 Drugs (See Table 8)

 

  

Many chemotherapeutic drugs have marrow suppression as a major toxicity; effects are dose-dependent and will occur in all recipients. In contrast, idiosyncratic reactions to a large and diverse group of drugs may lead to aplastic anemia without a clear dose-response relationship. These associations rest largely on accumulated case reports, but a massive international study in Europe in the 1980s quantitated drug relationships, especially for nonsteroidal analgesics, sulfonamides, thyrostatic drugs, some psychotropics, penicillamine, allopurinol, and gold. Not all associations necessarily reflect causation: a drug may have been used to treat the first symptoms of bone marrow failure (antibiotics for fever or the preceding viral illness) or provoked the first symptom of a preexisting disease (petechiae by nonsteroidal anti-inflammatory agents administered to the thrombocytopenic patient). In the context of total drug use, idiosyncratic reactions, while individually devastating, are exceedingly rare events. Chloramphenicol, the most infamous culprit, reportedly produced aplasia in only about 1/60,000 therapy courses, and even this number is almost certainly an overestimate (risks are almost invariably exaggerated when based on collections of cases; although the introduction of chloramphenicol was perceived to have created an epidemic of aplastic anemia, its diminished use was not followed by a changed frequency of marrow failure). Risk estimates are usually lower when determined in population-based studies; furthermore, the low absolute risk is also made more obvious: even a 10- or 20-fold increase in risk translates, in a rare disease, to but a handful of drug-induced aplastic anemia cases among hundreds of thousands of exposed patients.

Infections Hepatitis is the most common preceding infection, and posthepatitis marrow failure accounts for about 5% of etiologic associations in most series. Patients are usually young men who have recovered from a mild bout of liver inflammation 1 to 2 months earlier; the subsequent pancytopenia is very severe. The hepatitis is almost invariably seronegative (non-A, non-B, non-C, non-G) and presumably due to a novel, as yet undiscovered, virus. Fulminant liver failure in childhood can follow seronegative hepatitis, and marrow failure occurs at a high rate in these patients as well. Aplastic anemia can rarely follow infectious mononucleosis, and Epstein-Barr virus has been found in the marrow of a few aplastic anemia patients, some without a suggestive preceding history. Parvovirus B19, the cause of transient aplastic crisis in hemolytic anemias and of some pure red cell aplasia (see below), does not usually cause generalized bone marrow failure. Blood count depression is frequent in the course of many viral and bacterial infections but is comparatively moderate and resolves with the infection.

Immunologic Diseases Aplasia is a major consequence and the cause of death in transfusion-associated graft-versus-host disease, which can occur after infusion of unirradiated blood products to an immunodeficient recipient. Aplastic anemia is strongly associated with the rare collagen vascular syndrome called eosinophilic fasciitis, which is characterized by painful induration of subcutaneous tissues. Pancytopenia with marrow hypoplasia can also occur in systemic lupus erythematosus.

Pregnancy  Aplastic anemia very rarely may occur and recur during pregnancy and resolve with delivery or with spontaneous or induced abortion.

Paroxysmal Nocturnal Hemoglobinuria  An acquired mutation in the PIG-A gene in a hematopoietic stem cell is required for the development of PNH, but PIG-A mutations probably occur commonly iormal individuals. If the PIG-A mutant stem cell proliferates, the result is a clone of progeny deficient in glycosylphosphatidylinositol-linked cell surface membrane proteins. Such PNH cells are now most accurately enumerated using fluorescence-activated flow cytometry of CD55 or CD59 expression on granulocytes rather than Ham or sucrose lysis tests on red cells. Deficient cells can be detected in about a quarter of patients with aplastic anemia at the time of presentation. In addition, functional studies of bone marrow from PNH patients, even those with mainly hemolytic manifestations, show evidence of defective hematopoiesis. Patients with an initial clinical diagnosis of PNH, especially younger individuals, may later develop frank marrow aplasia and pancytopenia; patients with an initial diagnosis of aplastic anemia may suffer from hemolytic PNH years after recovery of blood counts. One explanation for the aplastic anemia/PNH syndrome is selection of the deficient clones, perhaps because they are favored for proliferation in the peculiar environment of immune-mediated marrow destruction.

Congenital Disorders  Fanconi’s anemia, an autosomal recessive disorder, manifests as progressive pancytopenia, increased chromosome fragility, congenital developmental anomalies, and an increased risk of malignancy. Patients with Fanconi’s anemia typically have short stature; cafe au lait spots; and anomalies involving the thumb, radius, and genitourinary tract. At least seven different genetic defects have been defined by complementation analysis. The most common, type A Fanconi’s anemia, is due to a mutation in FANCA. The function of the four cloned genes so far identified in Fanconi’s anemia remains unknown.

Patients with Shwachman-Diamond syndrome may develop pancreatic insufficiency, malabsorption, and neutropenia and are at risk of aplastic anemia. Dyskeratosis congenita is an X-linked disorder characterized by mucous membrane leukoplasia, dystrophic nails, reticular hyperpigmentation, and the later development of aplastic anemia in about half of patients. Mutation in the DKC1 (dyskerin) gene has been found in some cases.

PATHOPHYSIOLOGY

Bone marrow failure results from severe damage to the hematopoietic cell compartment. In aplastic anemia, replacement of the bone marrow by fat is apparent in the morphology of the biopsy specimen and magnetic resonance imaging of the spine; cells bearing the CD34 antigen, a marker of early hematopoietic cells, are greatly diminished; and in functional studies, committed and primitive progenitor cells are virtually absentѕin vitro assays have suggested that the stem cell pool is reduced to ^1% of normal in severe disease at the time of presentation. Qualitative abnormalities, such as limited number of operating stem cell clones or shortened telomere length, may follow from the quantitative deficiency, reflecting the shrunken and stressed state of hematopoiesis. An intrinsic stem cell defect exists for constitutional aplastic anemia, as cells from patients with Fanconi’s anemia exhibit chromosome damage and death on exposure to certain chemical agents, but there is no convenient mechanism for the propagation of an acquired genetic abnormality that would produce a hypoproliferative (as opposed to neoplastic) disease. Aplastic anemia does not appear to result from defective stroma or growth factor production.

Drug Injury  Extrinsic damage to the marrow follows massive physical or chemical insults such as high doses of radiation and toxic chemicals. For the more common idiosyncratic reaction to modest doses of medical drugs, altered drug metabolism has been invoked as a likely mechanism. The metabolic pathways of many drugs and chemicals, especially if they are polar and have limited water solubility, involve enzymatic degradation to highly reactive electrophilic compounds; these intermediates are toxic because of their propensity to bind to cellular macromolecules. For example, derivative hydroquinones and quinolones are responsible for benzene-induced tissue injury. Excessive generation of toxic intermediates or failure to detoxify the intermediates may be genetically determined and apparent only on specific drug challenge; the complexity and specificity of the pathways imply multiple susceptible loci and would provide an explanation for the rarity of idiosyncratic drug reactions.

Immune-Mediated Injury  The recovery of marrow function in some patients prepared for bone marrow transplantation with antilymphocyte globulin (ALG) first suggested that aplastic anemia might be immune-mediated. Consistent with this hypothesis was the frequent failure of simple bone marrow transplantation from a syngeneic twin, without conditioning cytotoxic chemotherapy, which also argued both against simple stem cell absence as the cause and for the presence of a host factor producing marrow failure. Laboratory data support an important role for the immune system in aplastic anemia. Blood and bone marrow cells of patients can suppress normal hematopoietic progenitor cell growth, and removal of T cells from aplastic anemia bone marrow improves colony formation in vitro. Increased numbers of activated cytotoxic T cells are observed in aplastic anemia patients and usually decline with successful immunosuppressive therapy; cytokine measurements suggest a predominant TH1 immune response (interferon g, interleukin 2, and tumor necrosis factor). Interferon and tumor necrosis factor induce Fas expression on CD34 cells, leading to apoptotic cell death; localization of activated T cells to bone marrow and local production of their soluble factors are probably important in stem cell destruction.

Early immune system events in aplastic anemia are not well understood. Many different exogeneous antigens appear capable of initiating a pathologic immune response, but at least some of the active T cells recognize true self-antigens. The rarity of occurrence of aplastic anemia despite common exposures (medical drugs, hepatitis virus) suggests that genetically determined features of the immune response can convert a normal physiologic response into a sustained abnormal autoimmune process.

 

CLINICAL FEATURES

History  Aplastic anemia can appear with seeming abruptness or have a more insidious onset. Bleeding is the most common early symptom; a complaint of days to weeks of easy bruising, oozing from the gums, nose bleeds, heavy menstrual flow, and sometimes petechiae will have beeoticed. With thrombocytopenia, massive hemorrhage is unusual, but small amounts of bleeding in the central nervous system can result in catastrophic intracranial or retinal hemorrhage. Symptoms of anemia are also frequent, including lassitude, weakness, shortness of breath, and a pounding sensation in the ears. Infection is an unusual first symptom in aplastic anemia (unlike in agranulocytosis, where pharyngitis, anorectal infection, or frank sepsis occur early). A striking feature of aplastic anemia is the restriction of symptoms to the hematologic system, and patients often feel and look remarkably well despite drastically reduced blood counts. Systemic complaints and weight loss should point to other etiologies of pancytopenia. History of drug use, chemical exposure, and preceding viral illnesses must often be elicited with repeated questioning.

Physical Examination  Petechiae and ecchymoses are often present, and retinal hemorrhages may be present. Pelvic and rectal examinations should be performed with great gentleness to avoid trauma; these will often show bleeding from the cervical os and blood in the stool. Pallor of the skin and mucous membranes is common except in the most acute cases or those already transfused. Infection on presentation is unusual but may be present if the patient has been symptomatic for a few weeks. Lymphadenopathy and splenomegaly are highly atypical of aplastic anemia. Cafe au lait spots and short stature suggest Fanconi’s anemia; peculiar nails, dyskeratosis congenita.

 

Fig. 45. Aplastic anemia. Oral leukoplakia in dyskeratosis congenita.

 

LABORATORY STUDIES

Blood  The smear shows large erythrocytes and a paucity of platelets and granulocytes. Mean corpuscular volume (MCV) is commonly increased. Reticulocytes are absent or few, and lymphocyte numbers may be normal or reduced. The presence of immature myeloid forms suggests leukemia or MDS; nucleated red blood cells suggest marrow fibrosis or tumor invasion; abnormal platelets suggest either peripheral destruction or MDS.

 

Fig. 46. This bone marrow film at 400X magnification demonstrates a complete absence of hemopoietic cells. Most of the identifiable cells are lymphocytes or plasma cells. Photographed by U. Woermann, MD, Division of Instructional Media, Institute for Medical Education, University of Bern, Switzerland.

 

 

Bone Marrow  The bone marrow is usually readily aspirated but appears dilute on smear, and the fatty biopsy specimen may be grossly pale on withdrawal; a “dry tap” suggests fibrosis or myelophthisis. In severe aplasia the smear of the aspirated specimen shows only red cells, residual lymphocytes, and stromal cells; the biopsy, which should be >1 cm in length, is superior for determination of cellularity and shows mainly fat under the microscope, with hematopoietic cells occupying, by definition, <25% of the marrow space. In the most serious cases the biopsy is virtually 100% fat. The correlation between marrow cellularity and disease severity is imperfect. Some patients with moderate disease by blood counts will have empty iliac crest biopsies, while “hot spots” of hematopoiesis may be seen in severe cases. If an iliac crest specimen is inadequate, cells should also be obtained by aspiration from the sternum. Residual hematopoietic cells should have normal morphology, except for mildly megaloblastic erythropoiesis; megakaryocytes are invariably greatly reduced and usually absent. Areas adjacent to the spicule should be searched for myeloblasts. Granulomas (in cellular specimens) may indicate an infectious etiology of the marrow failure.

 

Ancillary Studies  Chromosome breakage studies of peripheral blood using diepoxybutane (DEB) or mitomycin C should be performed on children and younger adults to exclude Fanconi’s anemia. Chromosome studies of bone marrow cells are often revealing in MDS and should be negative in typical aplastic anemia. Flow cytometric assays have replaced the Ham test for the diagnosis of PNH. Serologic studies may show evidence of viral infection, especially Epstein-Barr virus and HIV. Posthepatitis aplastic anemia is typically seronegative. The spleen size should be determined by scanning if the physical examination of the abdomen is unsatisfactory. Magnetic resonance imaging may be helpful to assess the fat content on a few vertebrae in order to distinguish aplasia from MDS.

 

DIAGNOSIS

The diagnosis of aplastic anemia is usually straightforward, based on the combination of pancytopenia with a fatty, empty bone marrow. Aplastic anemia is a disease of the young and should be a leading diagnosis in the pancytopenic adolescent or young adult. When pancytopenia is secondary, the primary diagnosis is usually obvious from either history or physical examination: the massive spleen of alcoholic cirrhosis, the history or metastatic cancer or systemic lupus erythematosus, or obvious miliary tuberculosis on chest radiograph.

Diagnostic problems can occur with atypical presentations and among related hematologic diseases. While pancytopenia is most common, some patients with bone marrow hypocellularity have depression of only one or two of three blood lines, sometimes showing later progression to more recognizable aplastic anemia. The bone marrow in constitutional or Fanconi’s anemia is indistinguishable morphologically from the aspirate in acquired disease. The diagnosis can be suggested by family history, abnormal blood counts since childhood, or the presence of associated anomalies of the skeletal and urogenital systems. Patients with Fanconi’s anemia may have no peculiar physical findings and can present with aplastic anemia as adults, in the third and fourth decades and, rarely, even later. Aplastic anemia may be difficult to distinguish from the hypocellular variety of MDS: MDS is favored by finding morphologic abnormalities, particularly of megakaryocytes and myeloid precursor cells, and typical cytogenetic abnormalities (see below).

PROGNOSIS

The natural history of severe aplastic anemia is rapid deterioration and death. Provision first of red blood cell and later platelet transfusions and effective antibiotics were of some benefit, but few patients showed spontaneous recovery. The major prognostic determinant is the blood count; severe disease is defined by the presence of two of three parameters: absolute neutrophil count <500/uL, platelet count <20,000/uL, and corrected reticulocyte count <1% (or absolute reticulocyte count <50,000/uL). Survival of patients who fulfill these criteria is about 20% at 1 year after diagnosis; patients with very severe disease, defined by an absolute neutrophil count <200/uL, fare even more poorly. Treatment has markedly improved survival in this disease.

TREATMENT

Treatment includes therapies that reverse the underlying marrow failure and supportive care of the pancytopenic patient. Severe acquired aplastic anemia can be cured by replacement of the absent hematopoietic cells (and the immune system) by stem cell transplant, or ameliorated by suppression of the immune system to allow recovery of the patient’s residual bone marrow function. Hematopoietic growth factors have limited usefulness and glucocorticoids are of no value. Suspect exposures to drugs or chemicals should be discontinued; however, spontaneous recovery of severe blood count depression is rare, and a waiting period before beginning treatment may not be advisable unless the blood counts are only modestly depressed.

Bone Marrow Transplantation  This is the best therapy for the young patient with a fully histocompatible sibling donor. HLA typing should be ordered as soon as the diagnosis of aplastic anemia is established in a child or younger adult. In transplant candidates, transfusion of blood from family members should be avoided so as to prevent sensitization to histocompatability antigens; while transfusions in general should be minimized, limited numbers of blood products probably do not seriously affect outcome.

For allogeneic transplant from fully matched siblings, long-term survival rates for children are about 80%. Transplant morbidity and mortality are increased among adults, due mainly to the increased risk of chronic graft-versus-host disease and serious infections. Graft rejection was historically a major determinant of outcome in bone marrow transplant for aplastic anemia; high rates of primary or secondary graft failure may be related to the pathophysiology of marrow failure as well as to alloimmunization from transfusions.

Most patients do not have a suitable sibling donor. Occasionally, a full phenotypic match can be found within the family and serve as well. Far more available are other alternative donors, either unrelated but histocompatible volunteers, or closely but not perfectly matched family members. Survival using alternative donors is about half that of conventional sibling transplants. These patients will be at risk for late complications, especially a higher rate of cancer, if radiation is used as a component of conditioning. The majority of adults who undergo alternative donor transplants succumb to transplant-related complications.

Immunosuppression  Used alone, ALG or antithymocyte globulin (ATG) induces hematologic recovery (independence from transfusion and a leukocyte count adequate to prevent infection) in about 50% of patients. The addition of cyclosporine to either ALG or ATG has further increased response rates to about 70 to 80% and especially improved outcomes for children and for severely neutropenic patients. Combined treatment is now standard for patients with severe disease. Hematologic response strongly correlates with survival. Improvement in granulocyte number is generally apparent within 2 months of treatment. Most recovered patients continue to have some degree of blood count depression, the MCV remains elevated, and the bone marrow cellularity returns towards normal only very slowly, if at all. Relapse (recurrent pancytopenia) is frequent, often occurring as cyclosporine is discontinued; most, but not all, patients respond to reinstitution of immunosuppression, and some responders become dependent on continued cyclosporine administration. Development of MDS, with typical marrow morphologic or cytogenetic abnormalities, occurs in about 15% of treated patients, usually but not invariably associated with a return of pancytopenia, and some patients develop leukemia. Although the laboratory diagnosis of PNH can generally be made at the time of presentation of aplastic anemia by flow cytometry, recovered patients showing frank hemolysis or, less commonly, thrombosis should be retested for PNH. Bone marrow examinations should be performed annually or if there is an unfavorable change in blood counts.

Horse ATG (ATGAM; Upjohn) is given at 40 mg/kg per day for 4 days; rabbit ALG (Thymoglobulin; SangStat), is administered at 3.5 mg/kg per day for 5 days. For ATG, anaphylaxis is a rare but occasionally fatal complication; allergy should be tested by a prick skin test with an undiluted solution and immediate observation; desensitization is feasible. ATG binds to peripheral blood cells, and therefore, platelet and granulocyte numbers may fall further during active treatment. Serum sickness, a flulike illness with a characteristic cutaneous eruption and arthralgia, often develops about 10 days after initiating treatment. Most patients are given methylprednisolone, 1 mg/kg per day for 2 weeks, to ameliorate the immune consequences of heterologous protein infusion. Excessive or extended glucocorticoid therapy is associated with avascular joint necrosis. Cyclosporine is administered orally at an initial dose of 12 mg/kg per day in adults (15 mg/kg per day in children), with subsequent adjustment according to blood levels obtained every 2 weeks. Trough levels should be between 150 and 200 ng/mL. The most important side effects of chronic cyclosporine treatment are nephrotoxicity, hypertension, seizures, and opportunistic infections, especially Pneumocystis carinii (prophylactic treatment with monthly inhaled pentamidine is recommended).

Most patients with aplastic anemia lack a suitable marrow donor and immunosuppression is the treatment of choice. Long-term survival is equivalent with transplantation and immunosuppression. However, successful transplant cures marrow failure, while patients who recover adequate blood counts after immunosuppression remain at risk of relapse and malignant evolution. Because of the excellent results in children, allogeneic transplant should always be performed in the pediatric population if a suitable sibling donor is available. Increasing age and the severity of neutropenia are the most important factors weighing in the decision between transplant and immunosuppression in adults who have a matched family donor: older patients do better with ATG and cyclosporine, while transplant is preferred if granulocytopenia is profound. Some reluctant patients may be treated by immunosuppression followed by transplant for failure to recover blood counts or occurrence of late complications.

Outcomes following both transplant and immunosuppression have improved with time. High doses of cyclophosphamide, without stem cell rescue, have been reported to produce durable hematologic recovery, without relapse or evolution to MDS, but this treatment can produce sustained severe neutropenia and response is often delayed. Novel immunosuppressive drugs such as mycophenolate mofetil may further improve outcome.

Other Therapies  The effectiveness of androgen therapy has not been verified in controlled trials, but occasional patients will respond or even demonstrate blood count dependence on continued therapy. For patients with moderate disease or those with severe pancytopenia who have failed immunosuppression, a 3- to 4-month trial is appropriate. Hematopoietic growth factors, granulocyte colony stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), and interleukin 3, are not recommended as initial therapy for severe aplastic anemia, and even their role as adjuncts to immunosuppression is not well defined. Some patients may respond to chronic administration of growth factors in combination after failing immunosuppression. Splenectomy may occasionally increase blood counts in relapsed or refractory cases.

Supportive Care  Meticulous medical attention is required so that the patient may survive to benefit from definitive therapy or, having failed treatment, to maintain a reasonable existence in the face of pancytopenia. First and most important, infection in the presence of severe neutropenia must be aggressively treated by prompt institution of parenteral, broad-spectrum antibiotics, usually ceftazadime or a combination of an aminoglycoside, cephalosporin, and semisynthetic penicillin. Therapy is empirical and must not await results of culture, although specific foci of infection such as oropharyngeal or anorectal abscesses, pneumonia, sinusitis, and typhlitis (necrotizing colitis) should be sought on physical examination and with radiographic studies. When indwelling plastic catheters become contaminated, vancomycin should be added. Persistent or recrudescent fever implies fungal disease: Candida or Aspergillus are common, especially after several courses of antibacterial antibiotics, and a progressive course may be averted by timely initiation of amphotericin. Granulocyte transfusions using G-CSF-mobilized peripheral blood have been effective in the treatment of overwhelming infections in a few patients. Hand washing, the single most effective method of preventing the spread of infection, remains a neglected practice. Nonabsorbed antibiotics for gut decontamination are poorly tolerated and not of proven value. Total reverse isolation is not clearly beneficial in reducing mortality from infections.

Both platelet and erythrocyte numbers can be maintained by transfusion. Alloimmunization limits the usefulness of platelet transfusions and can be avoided or minimized by several strategies, including use of single donors to reduce exposure and physical or chemical methods to diminish leukocytes in the product; HLA-matched platelets are often effective in patients refractory to random donor products. Inhibitors of fibrinolysis such as aminocaproic acid have not been shown to relieve mucosal oozing; the use of low-dose glucocorticoids to induce “vascular stability” is unproven. Whether platelet transfusions are better used prophylactically or only as needed remains unclear. Any rational regimen of prophylaxis requires transfusions once or twice weekly in order to maintain the platelet count >10,000/uL (oozing from the gut, and presumably also from other vascular beds, increases precipitously at counts <5000/uL). Menstruation should be suppressed either by oral estrogens or nasal follicle-stimulating hormone/luteinizing hormone (FSH/LH) antagonists. Aspirin and other nonsteroidal anti-inflammatory agents inhibit platelet function and must be avoided.

Red blood cells should be transfused to maintain a normal level of activity, usually at a hemoglobin value of 70 g/L (90 g/L if there is underlying cardiac or pulmonary disease); a regimen of 2 units every 2 weeks will replace normal losses in a patient without a functioning bone marrow. In chronic anemia, the iron chelator deferoxamine should be added at the time of the fiftieth transfusion in order to avoid secondary hemochromatosis.

 

 

References.

A – Main:

1. Davidson’s Principles and practice of medicine (21^st revised ed.) / by Colledge N.R., Walker B.R., and Ralston S.H., eds. – Churchill Livingstone, 2010. – 1376 p.

2. Harrison’s principles of internal medicine (18^th edition) / by Longo D.L., Kasper D.L., Jameson J.L. et al. (eds.). – McGraw-Hill Professional, 2012. – 4012 p.

3. The Merck Manual of Diagnosis and Therapy (nineteenth Edition)/ Robert Berkow, Andrew J. Fletcher and others. – published by Merck Research Laboratories, 2011.

4. Web -sites:

a) http://emedicine.medscape.com/

b) http://meded.ucsd.edu/clinicalmed/introduction.htm

B – Optional:

a. Lawrence M. Tierney, Jr. et al: Current Medical Diagnosis and treatment 2000, Lange Medical Books, McGraw-Hill, Health Professions Division, 2000.

b. On Line Resources:

http://image.bloodline.net/category.html

http://www.merckmanuals.com/professional/hematology_and_oncology/anemias_caused_by_deficient_erythropoiesis/decreased_erythropoiesis.html

http://www.merckmanuals.com/professional/hematology_and_oncology/anemias_caused_by_hemolysis/overview_of_hemolytic_anemia.html?qt=&sc=&alt=

http://bestpractice.bmj.com/best–practice/monograph/94/treatment/guidelines.html

http://www.gfmer.ch/Guidelines/Anemia_and_hemoglobinopathies/Anemia.htm