Pityriasis amiantacea: a distinctive presentation of psoriasis associated with tumour necrosis factor-α inhibitor therapy.

Pityriasis amiantacea (PA; also known as tinea amiantacea) is a relatively rare but distinctive scalp condition characterized by thick scales that adhere to each other and to the hair shaft, resulting in agglomeration and matting of hair. Temporary alopecia is a common complication. Although a specific cause remains unclear, PA is associated with several inflammatory diseases such as psoriasis and seborrhoeic dermatitis. We present a case of PA as a complication of underlying psoriasis, which developed during tumour necrosis factor (TNF)-α inhibitor therapy for Crohn disease. This paradoxical cutaneous reaction to anti-TNF-α therapy has been recently described as an emerging and perplexing cause of psoriasis and psoriasiform eruptions.