Megaloblastic Anemia - Causes

Causes

• Vitamin B12 deficiency leading to folate deficiency:
  • Achlorhydria-induced malabsorption
  • Deficient intake
  • Deficient intrinsic factor (pernicious anemia or gastrectomy)
  • Coeliac disease
  • Biological competition for Vitamin B12 by diverticulosis, fistula, intestinal anastomosis, and infection by the marine parasite Diphyllobothrium latum (fish tapeworm)
  • Selective Vitamin B12 malabsorption (congenital—juvenile megaloblastic anemia 1—and drug-induced)
  • Chronic pancreatitis
  • Ileal resection and bypass
  • Nitrous oxide anesthesia (usually requires repeated instances).

• Folate deficiency:
  • Alcoholism
  • Deficient intake
  • Increased needs: pregnancy, infant, rapid cellular proliferation, and cirrhosis
  • Malabsorption (congenital and drug-induced)
  • Intestinal and jejunal resection
  • (indirect) Deficient thiamine and factors (e.g., enzymes) responsible for folate metabolism.

• Combined Deficiency: Vitamin B12 & folate.

• Inherited Pyrimidine Synthesis Disorders: Orotic aciduria

• Inherited DNA Synthesis Disorders

• Toxins and Drugs:
  • Folic acid antagonists (methotrexate)
  • Purine synthesis antagonists (6-mercaptopurine)
  • Pyrimidine antagonists (cytosine arabinoside)
  • Phenytoin
  • Nitrous Oxide

• Erythroleukemia