Pellagra — DTM&H MCQ

Correct answer: C — Pellagra

Pellagra (option D) is correct because this man has the classic triad of niacin (vitamin B3) deficiency: photosensitive hyperpigmented dermatitis in a collar distribution (Casal necklace), diarrhoea, and neuropsychiatric change (irritability progressing to dementia if untreated), the so called 3 Ds. Maize is poor in bioavailable niacin and its precursor tryptophan unless alkali-treated (as in nixtamalisation), and diets low in animal protein or legumes further restrict tryptophan intake, explaining why maize-dependent, protein-poor communities are at particular risk. The photosensitive, symmetrical, sun-exposed distribution of the rash around the neck is the key discriminator that separates pellagra from other micronutrient deficiencies in this vignette. Why the other options are wrong: E. Scurvy: vitamin C deficiency causes perifollicular haemorrhage, corkscrew hairs, bleeding gums and poor wound healing, not a photosensitive neck dermatitis or diarrhoea. A. Zinc deficiency: causes acral and periorificial dermatitis (acrodermatitis enteropathica pattern), alopecia and diarrhoea, but the rash is not typically photosensitive or confined to sun-exposed skin like a Casal necklace. B. Riboflavin deficiency: presents with angular stomatitis, cheilitis and glossitis rather than a photosensitive dermatitis or prominent diarrhoea and mood change. D. Vitamin A deficiency: causes xerophthalmia, night blindness and follicular hyperkeratosis, not photosensitive dermatitis, diarrhoea or irritability as the leading features. Key point: A photosensitive, hyperpigmented dermatitis in a Casal necklace distribution with diarrhoea and neuropsychiatric symptoms in a maize-dependent, protein-poor diet points to niacin deficiency (pellagra).

Reference: British Journal of Medical Practitioners: Casal's Necklace (pellagra, niacin/vitamin B3 deficiency, clinical features and dietary risk factors), https://www.bjmp.org/content/casals-necklace