VITAMIN B₁₂ DEFICIENCY ANEMIA   26A

A 58-year-old woman presents to the emergency department with complaints of progressive fatigue and weakness for the past 6 months. She is short of breath after walking several blocks. On review of systems, she mentions mild diarrhea. She has noted intermittent numbness and tingling of her lower extremities and a loss of balance while walking. She denies other neurologic or cardiac symptoms and has no history of black or bloody stools or other blood loss. On physical examination, she is tachycardiac to 110 beats/min; other vital signs are within normal limits. Head and neck examination is notable for pale conjunctivas and a beefy red tongue with loss of papillae. Neurologic examination reveals decreased sensation to position and vibration in the lower extremities. Laboratory testing shows a low hematocrit level.

What are the salient features of this patient’s problem? How do you think through her problem?

Salient features: Fatigue, weakness and dyspnea of insidious onset; neurologic symptoms, including peripheral neuropathy and ataxia; tachycardia and paleness with anemia; glossitis; posterior column neurologic findings on examination

How to think through: The combination of two clinical presentations should raise the possibility of vitamin B₁₂ deficiency: anemia plus neurologic symptoms. Although peripheral neuropathy is the most common neurologic manifestation, what other neurologic symptoms can result from advanced vitamin B₁₂ deficiency? Regarding the anemia, in what range does the typical mean corpuscular volume (MCV) fall in vitamin B₁₂ deficiency; are there exceptions? What are the other common causes of macrocytic anemia? Specifically, what other metabolic derangements? Medication effects? Toxic ingestions? What are the findings on a peripheral blood smear in vitamin B₁₂ deficiency? What would the reticulocyte count be? Can this patient’s symptoms of fatigue, weakness, and dyspnea be caused by her anemia? In this patient, what would be the most common cause of vitamin B₁₂ deficiency? How would you diagnose it? What might be some other possible causes? Surgical? Infectious? Inflammatory? Dietary?

VITAMIN B₁₂ DEFICIENCY ANEMIA   26B

What are the essentials of diagnosis and general considerations regarding vitamin B ₁₂ deficiency?

Essentials of Diagnosis

Macrocytic anemia with serum vitamin B₁₂ level <100 pg/mL

Macro-ovalocytes and hypersegmented neutrophils on peripheral blood smear

General Considerations

Vitamin B₁₂ is absorbed from the diet (foods of animal origin) in the terminal ileum after binding to intrinsic factor, a protein secreted by gastric parietal cells, and stored in the liver.

Stores take at least 3 years to deplete after vitamin B₁₂ absorption ceases.

Causes of vitamin B₁₂ deficiency

    Decreased intrinsic factor production: pernicious anemia (most common cause), gastrectomy

    Dietary deficiency (only in vegans)

    Competition for vitamin B₁₂ in the gut: blind loop syndrome, fish tapeworm (rare)

    Decreased ileal vitamin B₁₂ absorption: surgical resection, Crohn disease

    Pancreatic insufficiency

    Helicobacter pylori infection

    Transcobalamin II deficiency (rare)

Pernicious anemia is associated with atrophic gastritis and other autoimmune diseases (e.g., immunoglobulin A [IgA] deficiency, polyglandular endocrine failure syndromes).

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