Pellagra — DTM&H MCQ
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Correct answer: D — Niacin (B3)
Explanation lettering: C = shown as A · D = shown as B · B = shown as C · A = shown as D
The correct answer is A, niacin (B3) deficiency, which causes pellagra. This patient has the classic triad of diarrhoea, symmetrical photosensitive dermatitis on sun-exposed skin, and confusion (the "3 Ds": diarrhoea, dermatitis, dementia), with a fourth D of death if untreated. Maize-dependent diets are the classic precipitant because niacin in maize is bound in an unavailable form (niacytin) and maize is also poor in tryptophan, the amino acid precursor from which the body can synthesise niacin. The combination of a cereal-dependent refugee diet with this specific symptom triad is pathognomonic for pellagra rather than any other micronutrient deficiency. Why the other options are wrong: B. Thiamine: deficiency causes beriberi (wet, with high output cardiac failure and oedema, or dry, with peripheral neuropathy) or Wernicke encephalopathy (ophthalmoplegia, ataxia, confusion), not photosensitive dermatitis or diarrhoea as the presenting triad. C. Cobalamin (B12): deficiency produces megaloblastic anaemia, subacute combined degeneration of the cord (sensory ataxia, peripheral neuropathy), and glossitis, but not a sun-exposed hyperpigmented dermatitis. D. Ascorbic acid (C): deficiency causes scurvy, with perifollicular haemorrhages, bleeding gums, poor wound healing and corkscrew hairs, not photosensitive dermatitis or dementia. E. Zinc: deficiency causes acrodermatitis enteropathica type lesions around the mouth, perineum and extremities, alopecia and diarrhoea, but the rash is not specifically photosensitive and confusion is not a typical feature. Key point: The triad of diarrhoea, photosensitive dermatitis, and dementia in a patient on a maize-heavy diet is diagnostic of pellagra from niacin deficiency, treated with oral nicotinamide.
Reference: Patient.info (Professional Reference, UK) - Pellagra: clinical features, causes and management, https://patient.info/doctor/dermatology/pellagra