Background

Megaloblastic anemia is an uncommon problem in childhood that is most frequently associated with vitamin deficiency or gastrointestinal disease. The megaloblastic effect is characterized by an aregenerative macrocytic anemia with nuclear dysmaturity, where the nucleus appears immature relative to the cytoplasm because of impaired DNA synthesis. See image below.

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. Photo courtesy of Marcel E Conrad, MD.

DNA synthesis is impaired in these cases because of inadequate amounts of metabolically active folate derivatives necessary for DNA base synthesis. Megaloblastic changes affect all 3 hematopoietic cell lines. Thrombocytopenia, leukopenia, and anemia are all observed to varying extents.

The 2 most common causes of megaloblastic anemia are vitamin B-12 (cobalamin) deficiency and folic acid deficiency. Although their clinical settings differ considerably, no hematologic finding can distinguish between the 2 conditions; specific testing is necessary (see Workup). Other less common causes include the use of metabolic inhibitors such as methotrexate and 6-mercaptopurine and certain rare inborn errors such as thiamine-responsive megaloblastic anemia,[1, 2] Lesch-Nyhan syndrome, and hereditary orotic aciduria (see Etiology).

Treatment of megaloblastic anemia depends on the underlying cause. Supplemental folate or vitamin B-12 may be indicated (see Treatment).

Go to Pediatric Chronic Anemia, Anemia of Prematurity, Donath-Landsteiner Hemolytic Anemia, Pediatric Acute Anemia, and Fanconi Anemia for complete information on these topics.

Vitamin B-12 deficiency

Vitamin B-12 is commonly ingested with meat or fish. It binds to salivary haptocorrins, which are digested in the stomach, allowing the cobalamin to bind to intrinsic factor (IF). IF is produced by the parietal cells of the stomach. The IF-B12 complex makes its way to the terminal ileum, where it binds to receptors on the enterocyte. It is transported across the cell and enters the circulation bound to a transport molecule, TC II. The B12-TC II complex is absorbed into cells by endocytosis. In the cell, cobalamin acts as a coenzyme in several reactions, including the

synthesis of methionine from homocysteine during the reduction of dihydrofolate to tetrahydrofolate and the conversion of methylmalonyl CoA to succinyl CoA. It is the role of vitamin B-12 in the reduction of folic acid derivatives that results in the megaloblastic changes seen clinically.

Vitamin B-12 deficiency can be caused by decreased ingestion (eg, poor dietary intake), impaired absorption (eg, failure to release B-12 from protein, IF deficiency, chronic pancreatic disease, competitive parasites, intrinsic intestinal disease), or impaired use (eg, congenital enzyme deficiencies, lack of transcobalamin II, administration of nitrous oxide).

Inadequate vitamin B-12 dietary intake is rare in children, though it may be seen in breastfed infants whose mothers are themselves deficient. Pernicious anemia, a common cause of vitamin B-12 deficiency in adults, is rare in childhood. Deficiency of vitamin B-12 activity is usually due to malabsorption or a congenital deficiency of one of the vitamin B-12 carrier proteins. In recent years, vitamin B-12 deficiency has been described in patients with human immunodeficiency virus (HIV) infection, with or without acquired immunodeficiency syndrome (AIDS).

In addition to the hematologic manifestations of vitamin B-12 deficiency, abnormalities of the GI tract and nervous system may also be present. The underlying cause of megaloblastic anemia must be determined in each case. Failure to recognize B-12 deficiency, even in the presence of concomitant folate deficiency, may result in permanent neurologic damage. Treatment with folate alone in these cases may reverse anemia but may allow neurologic damage to progress.

Folate deficiency

Folate is ingested in the diet in many different types of food. It enters the enterocyte and is transported into the portal circulation by a carrier molecule. It circulates in the plasma mostly as 5-methyl tetrahydrofolate (THF). It enters the cell via a carrier (methotrexate competes with this carrier). In the cell, folate binds to and acts as a coenzyme with enzymes responsible for single carbon metabolism.

Folate deficiency can be caused by any of the following:

Decreased ingestion (eg, poor dietary intake, alcoholism, infancy) Impaired absorption (eg, intestinal short circuits, celiac sprue, congenital malabsorption,

certain drugs such as sulfasalazine)

Impaired use (eg, use of folic acid antagonists such as antiepileptic medications, sulfa antibiotics, or methotrexate)

Increased requirements (eg, pregnancy, infancy, hyperthyroidism, chronic hemolytic disease, cancer)

Increased loss (eg, hemodialysis)

Folic acid is available in a wide variety of food groups. Approximately one third of dietary folate is estimated to come from cereals and grains, another third from fruits and vegetables, and

another third from meats and fish. Folic acid deficiency is commonly observed in children who are fed a severely restricted diet. This usually occurs with a diet restricted to goat's milk, which is deficient in folic acid. It may also be observed in children with celiac sprue and other malabsorption disorders that affect the proximal small intestine.

Deficiency of metabolically active folate metabolites is frequently observed in patients who receive antifolate drugs, such as sulfa antibiotics and methotrexate. A relative deficiency of metabolically active folate metabolites may also be observed in patients who are experiencing increased red cell destruction. These patients require a greater amount of folate than is usually present in the diet and develop macrocytic changes in their erythrocytes. Increased folate intake is also important during pregnancy, in which deficiencies have been associated with neural tube defects.

Pathophysiology

Megaloblastic anemia is caused by various DNA synthesis defects. In folate deficiency, purine biosynthesis is affected because folic acid is essential in this process.

Folic acid is essential for purine biosynthesis. Folic acid absorbed from the diet must be activated to produce active tetrahydrofolic acid (THF). THF is necessary for single carbon transfers in the synthesis of pyrimidine nucleotides. Without adequate levels of biologically active THF, the ability to repair and replicate DNA is decreased. Vitamin B-12 is a cofactor for the activation of folic acid in a step that also converts homocysteine to methionine.

In the case of inadequate folic acid intake, THF production is depleted, and DNA synthesis is slowed. The effect on hematopoiesis is to reduce the rate of cell production, resulting in pancytopenia. In the cells that are produced, the effect created is an arrest of nuclear maturation. In other words, the cells that are produced have immature nuclei compared with the degree of maturation of the cytoplasm.

Etiology

Megaloblastic anemia is most often caused by an acquired lack of vitamin B-12 or lack of folic acid. Inherited abnormalities of the metabolism of these nutrients may be the cause.[3]

Acquired causes of insufficient vitamin B-12 include the following:

Inadequate intake in diet Inadequate absorption (deficient IF; deficient absorption from ileum)

Impaired transport from the intestine

Acquired causes of insufficient folate include inadequate dietary intake and inadequate absorption from the proximal small intestine. Medications associated with folate deficiency include the following:

Sulfonamide antibiotics may interfere with folate metabolism, particularly when they are used on a long-term basis

Other antifolate antimetabolite drugs may also cause megaloblastic changes

Megaloblastic changes are observed with some frequency with antineoplastic agents, such as methotrexate; azathioprine (Imuran) may also cause megaloblastic changes

Increased metabolic demand (eg, chronic hemolysis, such as in sickle cell disease) or increased loss may also result in insufficient folate.

Congenital absence or deficiency of carrier proteins can cause vitamin B-12 deficiency. These deficiencies occur most commonly as autosomal recessive enzymopathies. These conditions often manifest during infancy and early childhood and are rare but important causes of megaloblastic anemia.

The Imerslund-Grasbeck syndrome of proteinuria and excretion of cobalamin and IF is a rare disorder that arises in early childhood. However, it is an important cause of B-12 deficiency

Epidemiology

The prevalence of megaloblastic anemia in childhood has not been established. Vitamin B-12 deficiency is a worldwide problem, however, particularly in the newborn period, due to the combined effects of poor maternal diet and congenital deficiencies of transcobalamin.

Pernicious anemia is a common cause of megaloblastic anemia, especially in persons of European or African descent. Dietary vitamin B-12 deficiency is a serious problem in India, Mexico, Central America, South America, and some areas of Africa. The increase in vegetarianism is related to an increase in vitamin B-12 deficiency and is a particular concern in breastfed infants of vitamin B-12–deficient mothers.

Megaloblastic anemia is observed in all racial and ethnic groups and in both sexes. It is rarely observed in infants, but may occur in infants who breastfeed from mothers who are themselves deficient in vitamin B-12 or in infants with a congenital deficiency of one of the carrier proteins.

Prognosis

Prognosis depends on the underlying cause of the megaloblastic anemia and the degree of compliance with therapy. Folic acid deficiency is relatively easy to treat; patients usually respond to added folate in their diet. Vitamin B-12 deficiency may be a more significant concern because some patients may require vitamin B-12 injections, with which they may not readily comply. In addition, vitamin B-12 deficiency may be associated with severe neurologic abnormalities that may be long lasting and persist even with appropriate vitamin B-12 therapy.

Morbidity in megaloblastic anemia may include CNS toxicity, including dementia and loss of dorsal column function. Deficiency of vitamin B-12 is usually at the root of this. CNS dysfunction has been described in adult patients who have deficient vitamin B-12 levels in the

absence of anemia. Megaloblastic anemia in pregnancy is associated with persistent learning deficits in children.[4, 5] Hyperpigmentation may also be seen.

Decreased numbers of CD4 cells and abnormal CD4/CD8 ratios as well as natural killer (NK) cell numbers have been documented in patients with pernicious anemia. These numbers normalize with cobalamin administration.[6]

Patient Education

For the new patient, education should focus on the nature of the deficiency causing the anemia and the underlying factors that produce the deficiency. Educate patients or their parents about the neurologic complications of vitamin B-12 deficiency to ensure that they understand the importance of B-12 replacement.

For patient education information, see the Esophagus, Stomach, and Intestine Center; Crohn Disease Center; and Blood and Lymphatic System Center, as well as Celiac Sprue, Crohn Disease, Diet and Nutrition in Crohn Disease, and Anemia.

History

Dietary history

A careful dietary history is essential to the diagnosis of megaloblastic anemia. The type and quantity of foods should be documented. In the case of a breastfed infant with megaloblastic anemia, the maternal dietary history should also be obtained.

Document dietary faddism or family-induced dietary restriction. Folate deficiency may result if the child's only source of dietary folic acid is goat's milk.

Children with one nutrient deficiency are at increased risk for other deficiencies; thus, search the history for evidence of other nutrient deficiencies.

Dietary vitamin B-12 deficiency in infants is extremely rare, but may occur in breastfed infants whose mothers are B-12 deficient. Obtain a careful history of the mother's diet. Include the mother's current diet, her diet while pregnant, and her diet before pregnancy. Vitamin B-12 deficiency is most common in women who have no meat in their diet.

GI disease

Carefully document the presence or absence of malabsorption syndromes, sprue, and preexisting conditions such as intestinal blind-loop syndrome or bowel resection. Evaluate for other acquired GI disorders, such as fish tapeworm infestation by Diphyllobothrium latum. Evaluate for Crohn disease and other causes of chronic inflammation of the ileum as potential causes of B-12

malabsorption. Carefully monitor for megaloblastic anemia due to impaired absorption of B-12 or folic acid following surgery involving the stomach, jejunum, or ileum.

Bone or joint pain, bruising, or bleeding

Bone and joint pain suggest that the child may have leukemia or another malignancy, with marrow replacement as the cause of pancytopenia. Bleeding and bruising are often observed in association with vitamin B-12 deficiency caused by thrombocytopenia, but these symptoms should also raise suspicion of leukemia or other marrow replacement disorders.

Medication

A history of sulfa exposure or use of antifolate antimetabolite chemotherapeutic agents, such as methotrexate, trimetrexate, or azathioprine, should be considered. Also consider the use of other antifolate drugs or drugs that affect the absorption of either folic acid or vitamin B-12. For example, certain anticonvulsants (eg, phenytoin, primidone) impair folate absorption.

Family history

Congenital absence or deficiency of carrier proteins is a common cause of vitamin B-12 deficiency. These deficiencies occur in families. Obtaining an extended family history is usually necessary to detect other affected family members. These conditions often manifest during infancy and early childhood and are rare but important causes of megaloblastic anemia because myelopathy and developmental delays occur without treatment.

Evaluate for Imerslund-Grasbeck syndrome of proteinuria and excretion of cobalamin and intrinsic factor (IF).

Physical Examination

The physical examination is largely directed by the findings of the history. Common findings include glossitis, stomatitis, hyperpigmentation, and weight loss.

Look for physical evidence of anemia, thrombocytopenia, and neutropenia. Pancytopenia can be observed in megaloblastic anemia, but it should raise the suspicion of a possible malignancy.

Evaluate for lymphadenopathy, hepatosplenomegaly, and abdominal or retroperitoneal masses as evidence of a malignancy.

Carefully document the neurologic status of a child with megaloblastic anemia. Document altered mental or neurologic status. Vibratory sensation in the extremities is frequently affected in vitamin B-12 deficiency.[7] These changes may reflect neurotoxicity from deficient B-12 levels. Once documented, these symptoms can be monitored to determine the degree of resolution once the child is B-12 replete.

Diagnostic Considerations

In a patient with combined folate and vitamin B-12 deficiency, if only the folate deficiency is recognized, folic acid supplementation may be sufficient to drive the production of active 5 methyl tetrahydrofolate (THF) in the absence of vitamin B-12. This results in improvement of the anemia but does not result in improvement of the function of other pathways dependent on B-12.

Clinically, this is apparent as a resolution of megaloblastic anemia, but with progressive dementia and long-tract neurologic deficits. This situation can be avoided by measuring levels of both vitamins, then evaluating and treating both deficiencies, if found.

Other conditions to consider include the following:

Aplastic anemia Celiac disease

Ecchymoses

Granulocytopenia

Hyposplenism

Myeloproliferative disorders

Neutropenia

Pancytopenia

Tapeworm infection (cestodiasis)

Imerslund-Grasbeck disease

Thiamine-responsive megaloblastic anemia[1, 2]

Go to Pediatric Chronic Anemia, Anemia of Prematurity, Donath-Landsteiner Hemolytic Anemia, Pediatric Acute Anemia, and Fanconi Anemia for complete information on these topics.

Differential Diagnoses

Acute Myelocytic Leukemia Anemia, Acute

Anemia, Chronic

Bone Marrow Failure

Hypopituitarism

Intestinal Protozoal Diseases

Lymphoproliferative Disorders

Malabsorption Syndromes

Malnutrition

Soy Protein Intolerance

Approach Considerations

Hematologic testing confirms the presence of megaloblastic anemia, and can exclude neoplastic and other disorders.

Assess for vitamin B-12 and folate levels.

Other tests include serum and urine assessments and the modified Schilling test.

Hematologic Evaluation

The CBC reveals macrocytic red cell indices and evaluates for other cytopenias. Pancytopenia has been observed in severe cases of megaloblastic anemia.

The manual differential is essential to rule out the possibility of circulating blast cells, which may be present in a patient with leukemia who presents with pancytopenia. A platelet count may be indicated.

The reticulocyte count is important in the assessment of red cell production.

Examination of the peripheral blood smear shows macrocytosis. Hypersegmented neutrophils (in which the nucleus has 6 or more segments) can usually be observed as well.

Consider bone marrow evaluation for any child with more than one abnormal cell line on the CBC. It can help to rule out other disorders such as leukemia, myelodysplasia, and aplastic anemia. Bone marrow in patients with megaloblastic anemia demonstrates the red blood cell precursor nuclear/cytoplasmic asynchrony. Granulocyte precursors may also be abnormal.

Vitamin B-12 and Folate Assessment

Measure serum vitamin B-12 levels. Methylmalonic acid and total homocysteine levels are sensitive indicators of vitamin B-12 deficiency and correlate with clinical abnormalities and

therapeutic response. However, they are not specific to vitamin B-12 deficiency, and care should be taken in interpreting these results.

For folate assessment, the RBC folate level is the best measure of metabolically active folate and includes 5-methyl tetrahydrofolate (THF) in the assay. Serum folate measures the circulating pool of folate but does not accurately reflect the amount of THF present in the tissues.

Serum and Urine Assessment

Serum chemistries should include albumin and total protein measurement.

Serum chemistry studies allow assessment of protein loss and nutritional status.

Urinalysis should be performed for protein and creatinine.

Measurement of urine proteins and intrinsic factor (IF), if possible, detects Imerslund-Grasbeck syndrome.[8]

Modified Schilling Test

When vitamin B-12 deficiency is suspected, a Schilling test may be performed to determine whether congenital absence of a binding protein is present. However, the classical nuclear medicine Schilling test is not commonly available due to the unavailability of radiolabeled B-12.

The Schilling test may be modified to avoid the need for radiolabeled B-12 by measuring B-12 levels before and after a known B-12 dose, followed by a similar test using B-12 with accompanying IF. A comparison of B-12 levels allows detection of a deficiency of either IF or IF-binding protein.

The significance of Schilling test results is as follows:

Elevation of the B-12 level with oral B-12 -Dietary insufficiency Elevation in B-12 levels with oral B-12 and IF - Deficiency of IF (ie, pernicious anemia)

No improvement with B-12 and IF - Either no absorption in the ileum or transport carrier protein deficiency

Approach Considerations

Treatment of megaloblastic anemia depends on the underlying cause. Folate deficiency due to dietary deficiency or increased demands is best treated with folate supplements. In addition, a diet rich in green, leafy vegetables is essential for normal intake of folic acid.

Folate deficiency caused by the use of sulfa drugs or other antifolate medications may be addressed by folate supplementation or by reducing or eliminating the drug. Folate deficiency due to celiac sprue requires treatment of the underlying disorder and folate supplements.

Vitamin B-12 deficiency is often more complex because of the nature of B-12 deficiency in childhood. Recent data, albeit from small trials, suggests that oral B-12 supplementation is as effective as parenteral supplementation in patients with nutritional deficiency. Even in patients with intrinsic factor (IF) deficiency, oral supplements may be effective, using higher doses.

Often, however, high-dose oral B-12 supplements are unsuccessful in patients with IF deficiency or who have undergone intestinal surgery. These patients may require parenteral supplementation because of impaired secretion or absorption of IF.

Because vitamin B-12 is contained exclusively in animal products (meat), vitamin supplementation is the only means of appropriate vitamin B-12 intake in individuals choosing vegetarian diets.

For children with congenital disorders that lead to B-12 deficiency, supplementation is a lifelong necessity; therefore, establishing a regimen that is tolerable over time is essential to maintaining compliance.

Go to Pediatric Chronic Anemia, Anemia of Prematurity, Donath-Landsteiner Hemolytic Anemia, Pediatric Acute Anemia, and Fanconi Anemia for complete information on these topics.

Consultations

Consultation with a pediatric gastroenterologist to evaluate for inflammation of the ileum or jejunum and assist in treatment planning is often helpful for patients with newly diagnosed Crohn disease or celiac sprue. A gastroenterologist may also be needed to evaluate the extent of liver disease, which may manifest with macrocytic erythrocytes.

Consider consulting a hematologist to evaluate the bone marrow for evidence of other marrow diseases that can manifest with macrocytic anemia and thrombocytopenia.

Medication Summary

The 2 most common causes of megaloblastic anemia are vitamin B-12 (cobalamin) deficiency and folinic acid deficiency. Treatment may require supplemental administration of these vitamins.

Vitamins

Class Summary

Vitamins are organic substances required by the body in small amounts for various metabolic processes. Vitamins may be synthesized in small or insufficient amounts in the body or not synthesized at all, thus requiring supplementation. Use folic acid and vitamin B-12 supplements as indicated.

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Folic acid (Folacin-800)

A member of the vitamin B group, folic acid is reduced in the body to 5 methyl tetrahydrofolate (THF), which is a coenzyme for various metabolic processes including purine and pyrimidine nucleotides synthesis essential for DNA. Folic acid is an important cofactor for enzymes used in production of red blood cells.

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Cyanocobalamin (CaloMist, Nascobal, Ener-B)

Deoxyadenosylcobalamin and hydroxocobalamin are active forms of vitamin B-12 in humans. Vitamin B-12 is synthesized by microbes but not humans or plants. Vitamin B-12 deficiency may result from inadequate dietary intake, intrinsic factor deficiency (pernicious anemia), partial or total gastrectomy, or diseases of the distal ileum.