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Updated: Feb 22 2017

Vitamin B12 (Cobalamin)

  • Snap Shot
    • A 59-year-old woman has the gradual onset of emotional lability, forgetfulness, and difficulty organizing her finances. PE reveals a bilateral Babinski sign.
  • Deficiency
    • Causes
      • pernicious anemia
        • intrinsic factor required for absorption in the terminal ileum
        • B12 not absorbed when intrinsic factor not produced from the parietal cells of the stomach
      • gastric bypass surgery
        • less intrinsic factor produced
      • resection of terminal ileum
        • e.g. Crohn's disease
      • malabsorption
        • sprue, enteritis, Diphyllobothrium latum
      • bacterial overgrowth of terminal ileum
      • vegan diets
    • Presentation
      • neurologic findings are unique to B12 deficiency
      • numbness and parastesias of the extremities
      • hyporeflexia
      • vibratory loss
      • ataxia
      • demetia
      • neurological deficits can occur even if hematology in normal
    • Evaluation
      • serum B12
      • increased methylmalonic acid and homocysteine levels
      • pancytopenia
      • Schillings Test
      • smear shows hypersegmented neutrophils, macroovalcytes
        • since B12 folate is needed in DNA synthesis, absence results in large immature nuclei in all nucleated cells in the marrow. Most of these abnormal cells are destroyed and therefore the patients present with pancytopenia
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