Renbok phenomenon and contact sensitization in a patient with alopecia universalis.

BACKGROUND Immune responses are largely regulated by cytokines that are secreted by activated T cells. Interactions among these cells are complex, and the interaction between 2 responses may alter the effect of either response alone. It has been established that contact sensitization-induced inflammation can reverse hair loss due to alopecia areata. In parallel, the Renbök phenomenon demonstrates how 2 distinct autoimmune diseases--psoriasis and alopecia areata--interact to result in clinically active psoriasis suppressing alopecia areata. OBSERVATIONS We describe a patient with concurrent psoriasis and alopecia universalis with terminal hairs within plaques on his extremities, representing the only normal hair growth on his body. Adjacent biopsy specimens confirmed our clinical suspicion of plaque psoriasis with normal hair follicles and alopecia universalis with a peribulbar lymphocytic infiltrate. Our patient's psoriatic plaques cleared rapidly with narrow-band UV-B phototherapy, but hair growth at the site was maintained. His scalp alopecia responded to squaric acid dibutylester contact sensitization therapy. CONCLUSIONS This case represents a natural experiment in which 3 distinct but overlapping immune responses favored psoriasis or contact dermatitis over alopecia areata. The precise mechanism responsible for these effects remains unclear; however, based on recent reports, we speculate that cytokine cross-regulation plays a role in competition among these distinct immune responses.