Vitamin B12 (Cobalamin) Deficiency
Etiology:
 • Vit B12 - aka cobalamin. Present in foods derived from animal products.
 • Common Causes - decreased dietary intake (e.g. in vegans), malabsorption (d/t reduced gastric acidity, medications, pancreatic dysfunction, and/or disorders of small intestine), autoantibodies (pernicious anemia, PA - impaired absorption 2/2 ab to intrinsic factor, IF)
Clinical Presentation:
 • Worsening macrocytic anemia, yellow skin, cognitive slowing, neuropathy, fatigue, wt loss
 • If anemia is severe, may have sx attributable to tissue hypoxia and organ ischemia (e.g. CP, SOB, lightheadedness, palpitations), skin pallor
 • GI - glossitis (pain, swelling, tenderness, loss of papillae of tongue), abd pain, diarrhea related to IBD, celiac disease, other malabsorptive state
 • Neuropsych - symmetric parasthesias, gait problems (think of subacute combined degeneration of dorsal 8 lateral columns)
 • Takes years to manifest its symptoms (in strict vegans who don't take B12 supplements) d/t large total body stores
Evaluation:
 • History - Diet, previously dx'd associated conditions, surgeries (bariatric, gastric, intestinal), alcohol use, symptoms
 • P/E - GI and derm findings, HSM, LN, peripheral neuropathy
 • Labs:
    - CBC, PBS - anemia, mild leukopenia and/or low pit, low retic count, hypersegmented neutrophils, macrocytosis
    - Low Vit B12 level (< 200 pg/mL) - not specific, can have spuriously elevated or low levels
    - Elevated MMA and homocysteine levels
    - Check for IF ab
Treatment:
 • Oral cobalamin 1000 - 2000 ug daily
 • Adequate amount of this will be absorbed, even if IF is lacking or there is malabsorption
 • If severe and need more rapid correction, can consider IM or IV
 • Response - reticulocytosis in several days, Hb level increases by approx. lg per week
 • If response is inadequate, consider other diagnosis e.g. leukemia

Dr. Joan Lee @taleanski
 
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