B12 Deficiency Cognitive Decline — MRCPsych Paper B MCQ

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EasyOld Age PsychiatryB12 Deficiency Cognitive DeclineMRCPsych Paper B

A 65-year-old man develops progressive forgetfulness, unsteadiness and symmetrical tingling in both feet. Examination shows reduced vibration and joint-position sense distally. Blood tests show a haemoglobin concentration of 102 g/L and a mean corpuscular volume of 116 fL; anti-intrinsic factor antibodies are present. Which potentially reversible cause of his cognitive symptoms is most strongly indicated?

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Correct answer: C — Vitamin B12 deficiency

Explanation lettering: C = shown as B · D = shown as C · E = shown as D · B = shown as E

D is correct. Macrocytic anaemia, cognitive decline, peripheral sensory symptoms and impaired vibration and joint-position sense form a characteristic vitamin B12-deficiency syndrome. Anti-intrinsic factor antibodies support autoimmune gastritis, historically termed pernicious anaemia, as the underlying cause. NICE lists macrocytosis, cognitive difficulties and peripheral neuropathy or myelopathy among the common features of vitamin B12 deficiency. Hypothyroidism can cause cognitive slowing and macrocytosis but does not explain the anti-intrinsic factor antibodies and posterior-column sensory pattern. Normal pressure hydrocephalus may cause cognitive and gait impairment but not macrocytic anaemia or neuropathy. Alzheimer's disease does not explain the systemic findings, while neurosyphilis is less consistent with the haematological and antibody results. Cognitive and neurological recovery after replacement may be slow or incomplete.

Reference: National Institute for Health and Care Excellence. NG239, Vitamin B12 deficiency in over 16s: diagnosis and management, sections 1.2 and 1.5, 2024. https://www.nice.org.uk/guidance/NG239/chapter/recommendations