Pellagra — DTM&H MCQ

Correct answer: C — Niacin deficiency

The correct answer is C, Niacin deficiency, which causes pellagra, the classic condition of populations reliant on unprocessed maize as a dietary staple. Maize is poor in bioavailable niacin and tryptophan, and unlike traditional nixtamalisation (lime treatment), untreated maize leaves niacin bound and unabsorbable, so prolonged maize-based food aid without fortification precipitates deficiency. Pellagra produces the classic triad of photosensitive dermatitis (typically symmetrical, on sun-exposed skin such as the neck, described as Casal's necklace), diarrhoea from gut mucosal atrophy, and dementia or cognitive change from neuronal degeneration, often summarised as the three (or four, with death) Ds. This constellation, in a patient dependent on maize aid, is pathognomonic for niacin deficiency and is treated with nicotinamide replacement. Why the other options are wrong: D. Vitamin C deficiency: causes scurvy with gum disease, perifollicular haemorrhages and poor wound healing, not photosensitive dermatitis, diarrhoea or dementia. A. Vitamin D deficiency: causes bone pain, myopathy and rickets/osteomalacia; it has no association with photosensitive rash or diarrhoea. E. Iodine deficiency: causes goitre, hypothyroidism and developmental delay in children, not dermatitis or diarrhoea. B. Thiamine deficiency: causes beriberi (wet with cardiac failure, dry with peripheral neuropathy) or Wernicke encephalopathy, but not a photosensitive dermatitis; diarrhoea and dementia can overlap but the specific sun-exposed rash is the discriminator against thiamine. Key point: photosensitive dermatitis plus diarrhoea plus dementia in someone reliant on unfortified maize is pellagra from niacin deficiency, treated with nicotinamide.

Reference: World Health Organization, Pellagra and its prevention and control in major emergencies (WHO/NHD/00.10), Department of Nutrition for Health and Development, https://www.cdc.gov/immigrant-refugee-health/media/pdfs/Pellagra-WHO.pdf