Niacin Deficiency
Pellagra
Pathology
Dermatitis
Pellagra manifests with a striking, symmetrical, well-defined cutaneous photosensitivity, and this is a prominent feature of the disease (Figure 1). The rash usually starts on the sun-exposed areas as erythema, and subsequently, the skin progresses to leathery hyperpigmented plaques.13, 14 Typically, the changes are not of classical dermatitis in late stages and can be recognised as distinct by a dermatologist. It can affect skin appendages such as nails.15
Two people (both from Malawi: the left patient in her 20s and the other in her 30s) with pellagra. Note the photodistributions affecting both and the “Casal's necklace” on the more severely affected patient on the right