Megaloblastic Anemia

Megaloblastic Anemia

 

Megaloblastic anemias are a group of macrocytic anemias in which the bone marrow shows megaloblastic erythropoieses.

Epidemiology

  • Incidence – macrocytosis occurs in 2-4% of the population
  • Age – more common in older adults

Etiology

  • Cobalamin deficiency (B12)
    • Malabsorption
      • Lack of intrinsic factor
    • Achlorhydria – most common in the elderly and patients on acid suppression
    • Postgastrectomy
    • Intestinal stasis due to anatomic lesions
    • Ileal abnormalities – tropical sprue
      • Inherited disorders of B12
  • Folic acid deficiency
    • Malabsorption, inadequate intake
    • Drugs
    • Metabolic disorders
    • Inherited disorders of folate
  • Combined deficiencies of folic acid and cobalamin are not uncommon

Clinical Presentation

  • Symptoms
    • Often based on the presence of anemia
    • Pale skin, anorexia, sore tongue, numbness, paresthesias
    • >50% present without anemia
  • Pernicious anemia – most common cause of B12 deficiency
    • Caused by absence of intrinsic factor (IF)
      • Often caused by autoimmune destruction of parietal cells (PCA)
      • 80% have PCA, 50% or greater have IF antibodies
    • Most common in patients of northern European descent
    • Increased incidence in patients with other autoimmune diseases such as Graves, vitiligo, hypoparathyroidism, Addison disease, Hashimoto thyroiditis

Diagnosis

  • Laboratory testing
    • Finding on smear of macrocytosis
      • Blood smear with macro ovalocytes, anisocytosis, hypersegmented nuclei in white blood cells
    • Low reticulocyte count
    • Testing of B12 and folate

Treatment

  • Folate replacement is oral
  • B12 replacement is parenteral or intranasal
    • In PA – lifelong replacement is necessary

See Also