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| Fig. 40.2 Pellagra, showing the typical photodistributed dermatitis on the neck and chest known as 'Casal’s necklace.' (Courtesy of Richard Gentry, MD.) |
The dermatitis is characteristically, but not invariably, photodistributed. Acutely, it is erythematous and may be associated with either pruritus or burning. Within 2 to 3 weeks, it becomes dry, scaly, and thickened. Casal’s necklace is a term used to describe sharply demarcated dermatitic lesions that develop around the neck and clinically resemble a necklace (Fig. 40-2). Dermatitic lesions also occur in the perineal and genital areas, over bony prominences, and on the face. The skin abnormalities in pellagra respond rapidly to niacin supplementation and heal in a centrifugal fashion.
