Anemia: Production Defects Part 4

Treatment

Specific replacement should be started promptly after the diagnosis has been made and serum samples have been taken to determine cobalamin levels. Patients who have a low serum cobalamin level and macrocytic anemia should undergo a trial of parenteral cobalamin therapy. The diagnosis of cobalamin deficiency is confirmed if cobalamin therapy produces a reticulo-cytosis in 3 to 4 days that is associated with a rise in the hemoglobin level and a fall in the MCV.

Table 4 Causes of Cobalamin Deficiency

Inadequate Diet

Strict vegetarianism

Inadequate Absorption

Gastric abnormalities that produce deficient or defective intrinsic factor

Pernicious anemia

Total gastrectomy Gastritis

Small bowel disease

Ileal resection or bypass

Blind loop syndrome with abnormal gut flora

Malabsorption

Tropical sprue

Crohn disease

Pancreatic insufficiency

Interference with Cobalamin Absorption

Drugs

Neomycin

Biguanides

Colchicine

Ethanol

Aminosalicylic acid

Omeprazole

Fish tapeworm competing for cobalamin

Degradation of Cobalamin Coenzymes

N2O anesthesia

Rare Congenital Disorders

Transcobalamin II deficiency

Defective intrinsic factor production

If the patient has symptoms of severe anemia, packed red blood cells can be transfused; the transfusion should be administered very slowly to avoid precipitating or aggravating congestive heart failure. This circumstance is one of the few in which a single-unit transfusion may be justified, because it may produce a 25% increase in oxygen-carrying capacity. A large dose of cobalamin should be given because the retention of pa-renterally administered cobalamin is poor but variable; the vitamin is inexpensive and has no harmful side effects. The reticulo-cyte response begins in 4 to 6 days, and the granulocyte count, if low, begins to increase at the same time. The hypersegmenta-tion of PMNs disappears after 10 to 14 days, which suggests that in the megaloblastic anemias, granulopoiesis is affected by cobalamin deficiency at two different steps: (1) the lobe number of the PMNs is determined, and (2) granulocytes mature and leave the marrow.55 Weekly dosages of 1,000 ^g of parenteral cobalamin for 6 weeks should be followed by parenteral dosages of 1,000 ^g monthly for life. The standard parenteral preparation is cyanocobalamin. For pancreatic insufficiency, cobalamin can be given parenterally or pancreatic enzymes can be administered orally. Specific therapy must be designed for patients with intestinal forms of malabsorption.

Because a small amount of cobalamin is absorbed even in the absence of IF and because only 1 ^g/day is required, oral cobal-amin has proved adequate for replacement in patients with pernicious anemia, freeing the patient from monthly injections (2,000 ^g/day p.o. is recommended).

Megaloblastic anemia caused by folic acid deficiency

Diagnosis

Clinical manifestations The patient with folic acid deficiency has a clinical presentation that is distinct from that of the patient with cobalamin deficiency.82 The patient may abuse alcohol or other drugs and have poor dietary intake of folic acid. Patients with folic acid deficiency are more often malnourished than those with cobalamin deficiency. The gastrointestinal symptoms in folic acid deficiency are similar to those in cobal-amin deficiency but may be more severe than those in pernicious anemia. Diarrhea is often present. The hematologic manifestations of folic acid deficiency are the same as those of cobal-amin deficiency: severe macrocytic anemia, a low absolute reticulocyte count, and a characteristic blood smear showing macro-ovalocytes, occasional megaloblasts, and hypersegment-ed neutrophils. Patients with megaloblastic anemia who do not have glossitis, a family history of pernicious anemia, or the neurologic features described for cobalamin deficiency may have folic acid deficiency.

Diagnostic workup A meticulous dietary history is important because food faddism, poor dietary intake, and alcoholism are the usual causes of severe folic acid deficiency [see Table 5]. Cobalamin and folic acid deficiencies frequently coexist and are not easily distinguished. In evaluating patients for folic acid deficiency, values for the levels of serum folic acid, serum cobal-amin, and red blood cell folic acid must be obtained. The red blood cell folic acid level reflects tissue stores83 but may be reduced in patients with severe cobalamin deficiency. In isolated cases, the serum folic acid level of cobalamin-deficient patients is usually normal or elevated. Severe, long-standing cobalamin deficiency leads to anorexia and GI disturbances, which may cause dietary folic acid deficiency. As a result, both serum cobalamin and folic acid levels are low, producing a double-deficiency state.

A serum folic acid level less than 2 ng/ml is consistent with folic acid deficiency, as is a red blood cell folic acid level less than 150 ng/ml. If the test results are inconclusive or if it is necessary to distinguish the megaloblastosis of folic acid deficiency from that of cobalamin deficiency, measurements of the serum methylmalonate and homocysteine levels are helpful. If both metabolite tests are normal (i.e., methylmalonate level of 70 to 270 nmol/L and total homocysteine level of 5 to 14 ^mol/L), deficiency of both vitamins is ruled out. If the methylmalonate level is normal but the total homocysteine level is increased, folic acid deficiency is likely and investigation into the underlying cause is appropriate.

Determining the underlying cause Folic acid deficiency is most frequently caused by poor dietary intake, but it may also result from inadequate absorption secondary to disease or drug administration [see Table 5]. Ingestion of ethanol by well-nourished individuals does not produce megaloblastosis, but in patients with borderline folic acid stores, ethanol can lower serum folic acid levels and block the reticulocyte response to folic acid administration. Alcohol may block release of folic acid from tissues to the serum.

Megaloblastic anemia occurring as a consequence of drug administration or pregnancy is likely to be caused by folic acid deficiency. Many of the antineoplastic and immunosuppressive agents produce megaloblastosis; these include fluorouracil, hy-droxyurea, mercaptopurine, thioguanine, cytarabine, and aza-thioprine. In pregnant women, the presence of megaloblastosis may not be initially apparent. Because the combination of folic acid and iron deficiency is common, full expression of mega-loblastosis is often blocked, and the patient will have a dimorphic anemia rather than the easily identifiable macro-ovalocyto-sis. Hypersegmentation of PMNs persists.

Table 5 Causes of Folic Acid Deficiency

Mechanism	Cause
Absolutely inadequate intake	Alcoholism
	Nutritional deficiencies
Relatively inadequate intake (resulting from increased folic acid requirements)	Pregnancy
	Severe hemolysis
	Chronic hemodialysis or peritoneal dialysis
Inadequate absorption	Tropical sprue
	Gluten-sensitive enteropathy (nontropical sprue)
	Crohn disease
	Lymphoma or amyloidosis of small bowel
	Diabetic enteropathy
	Intestinal resections or diversions
Drug-induced interference with folic acid metabolism	Action of dihydrofolate reductase blocked by methotrexate, trimethoprim, pyrimethamine
	Reduced folate absorption and tissue folate depletion caused by sulfasalazine
	Interference of unknown mechanism caused by phenytoin, ethanol, antituberculosis drugs, ?oral contraceptives

An abnormality in folate metabolism can be caused by a chromosomal mutation, and women who are homozygous for this defect are thought to be at higher risk for pregnancies affected by neural tube defects. One of the enzymes that regulates homo-cysteine levels, 5,10-methylenetetrahydrofolate reductase has a genetic variant, C677T. Individuals homozygous for this variant have increased plasma homocysteine levels that are lowered by folate supplementation. About 5% to 10% of the general population are homozygous for this variant. Both pregnant and non-pregnant women who are homozygous for the C677T mutation have significantly lower red blood cell folic acid levels.84 These women may be susceptible to cardiovascular disease and stroke and may bear children with neural tube defects.84,85 It would be advisable to know before pregnancy that a woman is homozy-gous for this variant, and genetic testing would be helpful if a woman has a family history of this defect.

A number of intestinal disorders cause folic acid deficiency. These include severe pancreatic disease and small bowel disease, including malabsorption, ileal disease, Crohn disease, resection, and bypass [see Table 5]. When there is no apparent cause of cobalamin deficiency, it may be practical to suspect an undiagnosed disease of malabsorption. In one prospective study of patients who had laboratory-defined folate deficiency, 10.9% were positive for celiac disease antibodies and 4.7% had histologically confirmed celiac disease.86

Treatment

Standard therapy for folic acid deficiency is 1 mg/day orally. The response, manifested by reticulocytosis in 4 to 6 days, loss of megaloblastosis, and the return of normal blood counts, confirms the diagnosis of folic acid deficiency. Neutrophil hyper-segmentation disappears only after 10 to 14 days, however.60 Patients with megaloblastosis and severe bone marrow depression secondary to administration of drugs that block dihydrofolate reductase, such as pyrimethamine and methotrexate, may be treated with folinic acid. In the case of toxicity after single large doses of methotrexate, a single equivalent dose of I.M. folinic acid (i.e., milligram for milligram) will suffice. For toxicity after chronic pyrimethamine therapy, 1 to 5 mg of folinic acid daily can be given without blocking the antimalarial effects of pyrimethamine. Megaloblastosis caused by anticonvulsant therapy can be treated with 1 mg of folic acid daily. Supplementation during pregnancy is advised and may also be useful for patients who have severe chronic hemolysis.

In most patients (i.e., those who do not require a large amount of folic acid because of conditions such as hemolysis or pregnancy), a hematologic response occurs after administration of 200 ^g of folic acid daily. The increased demand of folic acid during pregnancy requires administration of about 200 to 300 ^g/day.87 Furthermore, folic acid supplementation seems to prevent fetal neural tube defects.88 Such neural tube defects may occur in the embryo or very early in gestation—even before the pregnancy is confirmed.89,90 Therefore, it is recommended that women of childbearing age or those who plan to become pregnant receive about 400 ^g of folic acid a day. Women who are homozygous for the C677T mutation should also take folic acid supplements. Staple foods such as flour and cereal grains can be fortified with folic acid. Concern has been expressed, however, that folic acid supplementation may mask the megaloblastosis of pernicious anemia, causing the development of severe neuropathy rather than anemia.89

Sideroblastic Anemias

Definition

The sideroblastic anemias are a heterogeneous group of disorders characterized by anemia, ringed sideroblasts in the marrow, and ineffective erythropoiesis.91 There are hereditary and acquired forms; the latter are subdivided into benign and malignant variants. A fairly common form is the myelodysplastic syndrome called refractory anemia with ringed sideroblasts. Other than alcohol and drugs (e.g., isoniazid), the secondary causes of these diseases remain largely unknown.

Figure 8 Prussian blue stain shows ringed sideroblasts in the bone marrow of a patient who has idiopathic sideroblastic anemia.

Table 6 Sideroblastic Anemias

Type	Disorders
Hereditary variant, probably benign	Sex-linked disorders, autosomal disorders
Acquired variant, probably benign	Mitochondrial DNA deletions (Pearson syndrome)
Probably benign variant	Induced by drugs (e.g., isoniazid or other antituberculosis drugs) or by lead intoxication; alcoholic sideroblastosis; pyridoxine-responsive anemia
Clonal disorder (myelodysplastic syndrome)	Refractory anemia with ringed sideroblasts, acquired idiopathic sideroblastic anemia

Pathophysiology

Abnormalities of heme synthesis are probably the most frequent cause of the hereditary sideroblastic anemias. Molecular defects of the enzyme 5-aminolevulinate synthase have been described as the cause of this abnormality.90,92 This enzyme initiates the heme synthetic pathway, and its impairment profoundly affects heme synthesis. In other cases, there are major deletions in mitochondrial DNA. Iron enters erythroid precursors, but because heme synthesis is impaired, the iron cannot be incorporated into heme and accumulates on the cristae of mitochondria.90

Diagnosis

The principal feature common to all sideroblastic anemias is a refractory or progressive anemia. However, mild, lifelong anemia may go unnoticed. The diagnosis of sideroblastic anemia is established by reticulocytopenia; the red blood cells on smear are frequently profoundly hypochromic and microcytic, and distorted red blood cells and basophilic stippling may be noted.93,94 Occasionally, Pappenheimer bodies (deposits of iron that stain with the Prussian blue reagent) are present in the red blood cells. There are ringed sideroblasts seen on the marrow aspirate (bone marrow normoblasts with heavy incrustations of nonferritin iron on the mitochondria) [see Figure #]. Because of ineffective erythropoiesis, there is saturation of serum iron-binding capacity (usually approaching 80%) and elevation of the serum lactate dehydrogenase level. Cytogenetic study of the bone marrow may reveal one of the typical patterns seen in the myelodysplastic syndromes. The sideroblastic anemias can be classified into four groupings: hereditary (probably benign), acquired (probably benign), probably benign, and clonal disorder [see Table 6].

Treatment

For prognostic purposes, it is important to decide whether the patient has a benign or malignant form of sideroblastic anemia. It is also important to recognize reversible forms of sideroblastic anemia (e.g., those caused by alcoholism, folic acid deficiency, and drugs such as isoniazid and chloramphenicol) and to discontinue any potentially offending agents.

Indicators of myelodysplasia include granulocytopenia, thrombocytopenia, dysplastic marrow granulopoiesis, bilobed megakaryocytes, and typical cytogenetic abnormalities. In rare cases, patients have a reticulocyte and hemoglobin response to pyridoxine (200 to 600 mg/day), with or without folic acid.