Vitamin B12 deficiency develops when the body cannot absorb or does not get enough B12, as in pernicious anemia, after gastric surgery, with long-term metformin or on a strict vegan diet. It causes a macrocytic anemia and damage to nerves and the spinal cord that can become permanent if treated late.
Key symptoms
- Fatigue, pallor and shortness of breath
- Numbness and tingling in the feet and hands
- Unsteady walking and falls
- Memory problems, low mood or confusion
- Sore, smooth tongue
What you find on exam
- Pallor and a smooth red tongue (glossitis)
- Reduced vibration and position sense in the feet
- Positive Romberg test and unsteady gait
- Mild jaundice from breakdown of red cells
Tests
- Blood count: high MCV, sometimes low platelets and white cells
- Serum B12; methylmalonic acid if borderline
- Intrinsic factor antibodies for pernicious anemia
- Peripheral smear: hypersegmented neutrophils
Treatment basics
- Cyanocobalamin injections, then monthly maintenance
- High-dose oral B12 for mild or diet-related deficiency
- Lifelong treatment for pernicious anemia
- Check potassium early in severe anemia
- Treat the cause and recheck the blood count
Red flags
- Spinal cord signs: leg weakness or severe gait problems
- Severe anemia with chest pain or heart failure
- Confusion or psychosis
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Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.