B12 Deficiency — MRCPsych Paper B MCQ

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EasyOld Age PsychiatryB12 DeficiencyMRCPsych Paper B

A 65-year-old woman with depression follows a strict vegan diet and does not take vitamin supplements or consume fortified foods. She develops macrocytic anaemia, peripheral neuropathy and progressive cognitive difficulties. Which vitamin deficiency most likely accounts for this combination?

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Correct answer: A — Vitamin B12 (cobalamin)

The correct answer is A, vitamin B12 deficiency. A vegan diet without supplements or fortified foods is a recognised risk factor. The combination of macrocytic anaemia, peripheral neuropathy and cognitive or depressive symptoms is particularly characteristic of B12 deficiency. Folate deficiency can also cause macrocytic anaemia, but it does not characteristically produce the neurological syndrome seen here. Thiamine deficiency may cause peripheral neuropathy and Wernicke–Korsakoff syndrome in severe malnutrition or alcohol dependence, but it does not explain the macrocytic anaemia. Vitamins C and D do not fit this haematological and neurological presentation. NICE recommends testing for B12 deficiency when a relevant symptom or sign coexists with a risk factor such as a diet low in animal-source foods.

Reference: National Institute for Health and Care Excellence. Vitamin B12 deficiency in over 16s: diagnosis and management. NICE guideline NG239, recommendations 1.2.4–1.2.5 and Boxes 1–2, 2024. https://www.nice.org.uk/guidance/ng239/chapter/recommendations