(BMJ)—An 80-yo woman presented w/ an itchy rash on both hands and scalp x5mo. Symptomatic tx had been ineffective. Exam: dark, thickened skin on dorsal surfaces of hands bilaterally. Labs: antinuclear antibody neg; scalp bx showed scarring alopecia. What is the dx?
Riboflavin deficiency
Pemphigus vulgaris
Actinic reticuloid
Pellagra
Variegate porphyria
You are correct. Pellagra, a photodermatosis, results from deficiency of vitamin B3 (niacin). It usually starts as an itchy rash. Half of pts develop GI sx, and mood disturbance is common. Death can result from severe or prolonged deficiency. Dietary niacin deficiency is the most common cause worldwide, although malabsorption should also be considered. In primary niacin deficiency, tx w/ oral vitamin B3 results in improvement w/in days. This pt was treated w/ vitamin B3 for 2mo, and the rash cleared completely.

BMJ 2018;360:k68