Renbök phenomenon in an alopecia areata patient with psoriasis.

The Renbök phenomenon designates the withdrawal of a lesion when a different one appears. We describe a 23-year-old patient with psoriasis, who experienced regression of a psoriatic plaque on the scalp concurrently with the appearance of a patch of alopecia areata (AA). In 3 months, plaques of psoriasis appeared inside the patch of hair loss, accompanied by terminal hair growth in the plaques. Such rapid interchange between these two autoimmune disorders have not been described previously, and might reflect a quick substitution between two different T-cell populations, namely Th-17 and Th-1. Better understanding of the trigger for such an exchange can help in elucidating the pathogenesis for AA.