Chapter 100. Megaloblastic Anemias (Part 12)

Nutritional Dietary folate deficiency is common. Indeed, in most patients with folate deficiency a nutritional element is present. Certain individuals are particularly prone to have diets containing inadequate amounts of folate (Table 100-5). In the United States and other countries where fortification of the diet with folic acid has been adopted, the prevalence of folate deficiency has dropped dramatically and is now almost restricted to high-risk groups with increased folate needs. Nutritional folate deficiency occurs in kwashiorkor and scurvy and in infants with repeated infections or who are fed solely on goats milk, which has a low folate content.MalabsorptionMalabsorption...
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Chapter 100. Megaloblastic Anemias (Part 12) Chapter 100. Megaloblastic Anemias (Part 12) Nutritional Dietary folate deficiency is common. Indeed, in most patients with folatedeficiency a nutritional element is present. Certain individuals are particularlyprone to have diets containing inadequate amounts of folate (Table 100-5). In theUnited States and other countries where fortification of the diet with folic acid hasbeen adopted, the prevalence of folate deficiency has dropped dramatically and isnow almost restricted to high-risk groups with increased folate needs. Nutritionalfolate deficiency occurs in kwashiorkor and scurvy and in infants with repeatedinfections or who are fed solely on goats milk, which has a low folate content. Malabsorption Malabsorption of dietary folate occurs in tropical sprue and in gluten-induced enteropathy. In the rare congenital syndrome of selective malabsorptionof folate, there is an associated defect of folate transport into the cerebrospinalfluid, and these patients show megaloblastic anemia, which responds tophysiologic doses of folic acid given parenterally but not orally. They also showmental retardation, convulsions, and other central nervous system abnormalities.Minor degrees of malabsorption may also occur following jejunal resection orpartial gastrectomy, in Crohns disease, and in systemic infections but, in theseconditions, if severe deficiency occurs, it is usually largely due to poor nutrition.Malabsorption of folate has been described in patients receiving salazopyrine,cholestyramine, and triamterene. Excess Utilization or Loss Pregnancy Folate requirements are increased by 200–300 µg to ~400 µg daily in anormal pregnancy, partly because of transfer of the vitamin to the fetus, butmainly because of increased folate catabolism due to cleavage of folate coenzymesin rapidly proliferating tissues. Megaloblastic anemia due to this deficiency isprevented by prophylactic folic acid therapy. It occurred in 0.5% of pregnancies inthe UK and other Western countries before prophylaxis with folic acid, but theincidence is much higher in countries where the general nutritional status is poor. Prematurity The newborn infant, whether full term or premature, has higher serum andred cell folate concentrations than the adult. However, the newborn infantsdemand for folate has been estimated to be up to 10 times that of adults on aweight basis, and the neonatal folate level falls rapidly to the lowest values atabout 6 weeks of age. The falls are steepest and are liable to reach subnormallevels in premature babies, a number of whom develop megaloblastic anemiaresponsive to folic acid at about 4–6 weeks of age. This occurs particularly in thesmallest babies ( Inflammatory Conditions Chronic inflammatory diseases, such as tuberculosis, rheumatoid arthritis,Crohns disease, psoriasis, exfoliative dermatitis, bacterial endocarditis, andchronic bacterial infections, cause deficiency by reducing the appetite and byincreasing the demand for folate. Systemic infections may also causemalabsorption of folate. Severe deficiency is virtually confined to the patients withthe most active disease and the poorest diet. Homocystinuria This is a rare metabolic defect in the conversion of homocysteine tocystathionine. Folate deficiency occurring in most of these patients may be due toexcessive utilization because of compensatory increased conversion ofhomocysteine to methionine. Long-Term Dialysis As folate is only loosely bound to plasma proteins, it is easily removedfrom plasma by dialysis. In patients with anorexia, vomiting, infections, andhemolysis, folate stores are particularly likely to become depleted. Routine folateprophylaxis is now given. Congestive Heart Failure, Liver Disease Excess urinary folate losses of >100 µg per day may occur in some of thesepatients. The explanation appears to be release of folate from damaged liver cells.