Correct Answer: A. Niacin
This is a classic presentation of pellagra, the niacin (vitamin B3) deficiency syndrome. The discriminating clinical triad is diarrhea + dermatitis (neck lesion shown) + dementia (the "4 Ds": diarrhea, dermatitis, dementia, death). Maize as a staple diet is a well-recognized risk factor in India, particularly in rural populations, because niacin in maize is bound in a form that is poorly bioavailable unless the grain undergoes alkali treatment (nixtamalization, not common in Indian food preparation). Niacin functions as a coenzyme in NAD/NADP-dependent redox reactions critical for energy metabolism and DNA repair. Deficiency impairs mucosal integrity (causing diarrhea), epidermal turnover (causing the characteristic symmetric, photosensitive dermatitis in sun-exposed areas like the neck), and neuronal function. The dermatitis of pellagra is pathognomonic: sharply demarcated, erythematous, scaling lesions in a "glove and stocking" or "necklace" distribution over sun-exposed skin—exactly what the image likely shows. This is distinct from other vitamin deficiencies and is the key diagnostic clue in this question.
Why the other options are wrong
B. Zinc — Zinc deficiency causes acral dermatitis (around orifices and extremities) in acrodermatitis enteropathica or zinc malabsorption, but does NOT cause the characteristic necklace-distribution photosensitive dermatitis of pellagra. Zinc deficiency also presents with alopecia, diarrhea, and immune dysfunction, but the dermatitis pattern and the maize-staple diet history point away from zinc. NBE may pair zinc with diarrhea to trap students who don't recall the specific dermatitis pattern. C. Thiamine — Thiamine (vitamin B1) deficiency causes beriberi (wet or dry forms) and Wernicke-Korsakoff syndrome, characterized by neurological symptoms (peripheral neuropathy, ataxia, ophthalmoplegia), not the symmetric photosensitive dermatitis shown. Thiamine deficiency does not produce the necklace lesion or the specific mucosal changes seen in pellagra. The maize-staple diet is not a classic risk for thiamine deficiency in India. D. Iron — Iron deficiency causes microcytic hypochromic anemia with symptoms like fatigue, dyspnea, and glossitis, but NOT the characteristic photosensitive dermatitis or the specific diarrhea pattern of pellagra. Iron deficiency does not produce the necklace-distribution skin lesion. The clinical presentation—diarrhea + neck dermatitis—is not typical of iron deficiency.
High-Yield Facts
- Pellagra = niacin deficiency; classic triad is diarrhea + dermatitis (necklace/photosensitive) + dementia (4 Ds).
- Maize as staple diet is a major risk factor for pellagra in India because niacin is bound and poorly bioavailable unless alkali-treated.
- Niacin functions as NAD/NADP coenzyme; deficiency impairs energy metabolism, mucosal integrity, and epidermal turnover.
- Pellagra dermatitis is sharply demarcated, erythematous, scaling, and symmetric in sun-exposed areas (necklace, glove-and-stocking pattern).
- Treatment: niacin supplementation 50–500 mg/day oral; dietary sources include meat, peanuts, fortified cereals (rare in rural India).
Mnemonics
4 Ds of Pellagra Diarrhea, Dermatitis, Dementia, Death — remember in order of progression. The dermatitis is photosensitive and appears in a necklace distribution. Maize = Niacin Risk Maize staple diet → niacin bound/unavailable → pellagra. Alkali treatment (nixtamalization) releases niacin, but not done in typical Indian maize preparation.
NBE Trap
NBE pairs diarrhea with zinc deficiency (both cause GI symptoms) to trap students who don't recall the pathognomonic photosensitive dermatitis pattern unique to pellagra. The "neck lesion" image is the discriminator.
Clinical Pearl
In rural India, pellagra is still encountered in populations subsisting on maize without dietary diversity or fortified grain. The necklace dermatitis is so characteristic that it is sometimes called "Casal's necklace"—recognizing it clinically can prevent misdiagnosis as dermatitis from other causes and allows rapid niacin supplementation to prevent progression to dementia and death.
_Reference: Robbins Ch. 8 (Nutritional Disorders); KD Tripathi Ch. 29 (Vitamins); Harrison Ch. 75 (Nutritional Deficiencies)_