Casal's necklace

An 18-year-old male presented with a 2-week history of hyperpigmented scaly plaque associated with mild burning and itching. There was characteristic involvement of the front and nape of the neck and lower half of the face in a sharply demarcated symmetrical manner [Figure 1]. In addition, the lesion extended to the anterior aspect of the chest resembling a ‘cravat’. He had associated photosensitivity but no history of diarrhoea or neurological symptoms. There was no history of antecedent drug use, alcohol abuse or topical application. The patient used to stay alone and had poor dietary habits. A skin biopsy showed irregular acanthosis, lymphocytic exocytosis and spongiosis along with focal basal cell vacuolar degeneration [Figure 2]. A diagnosis of pellagra was made, and he was started on oral nicotinamide 500 mg daily with which he started responding within 3 days and lesions cleared completely within a week [Figure 1].

Figure 1: (a) Sharply demarcated plaque on the neck; (b) clinical response after treatment with nicotinamide 500 mg daily for 1 week

Figure 2: Histopathology (H and E, ×10) showing irregular acanthosis, lymphocytic exocytosis and spongiosis along with focal basal cell vacuolar degeneration

Conflicts of interest. None declared