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.

INTRODUCTION

In 1991, Happle et al. coined the term “Renbök” phenomenon to describe the opposite of the Koebner phenomenon, designating the withdrawal of a lesion with the appearance of another one.[1] It was originally described in alopecia areata (AA) patients experiencing hair growth in psoriatic lesions.[1] Although psoriasis can often co-exist with AA,[2] reports on psoriasis-induced Renbök phenomenon in AA have been exceedingly sparse, and did not demonstrate the interchanging nature of these two disorders.[3456]

CASE REPORT

A 23-year-old female patient presented in April 2012 with a flare of psoriasis, involving the trunk, extremities and the scalp. She had a similar flare at the age of 13, and also history of patch-type scalp AA, both resolved following topical steroid treatment. Two months later, in June 2012, she experienced localized hair loss on the scalp, concomitantly with complete resolution of the psoriatic plaque in this region. On examination, a 3 cm patch of nonscarring hair loss was observed, and dermoscopic examination revealed perifollicular pigmentation, exclamation hairs and yellow dots, corresponding to AA. Interestingly, the psoriatic plaque engulfed the AA area, but sharply stopped at its border [Figure 1a]. The patient was treated topically for her AA with clobetasol propionate, with stabilization of hair loss when the patch reached a size of 5 cm × 6 cm in September 2012. In parallel, the patient had reappearance of psoriatic plaques inside the area of hair loss, which coincided with the presence of terminal hairs localized to these psoriatic plaques [Figure 1b].

Figure 1

(a) A 3-cm diameter patch of hair loss on the scalp. A thick psoriatic plaque is shown adjacent to the area of hair loss, but sharply stops at its border. (b) Plaques of psoriasis appear inside the area of hair loss, accompanied by thick terminal hairs

DISCUSSION

AA is believed to be an autoimmune T-cell mediated disease, although its exact mechanism is still obscure.[7] While it has been reported to occur in association with other autoimmune disorders, such as vitiligo, colocalization of these two disorders remains a rare clinical entity.[8] Colocalization with psoriasis, another autoimmune disease, is also rare, and usually there is remission of AA in psoriatic plaques, the so called Renbök phenomenon.

The mechanism underlying the Renbök phenomenon is not entirely clear, although recent advances in the understanding of the pathogenesis of AA and psoriasis point to the possibility that changes in the local cytokine milieu based on the presence of different T-cell populations, result in interchange between these two disorders. Psoriasis is a Th-17-mediated disease,[9] while AA is presumed to be a Th-1 mediated disorder.[10] Each inflammatory pathway increases its own response and inhibits opposing pathways, therefore preventing the co-existence of two different diseases in the same location. The trigger for the switching point between one pathway to the other is unknown, and the Renbök phenomenon offers an exclusive opportunity to dissect this elusive point.

Our patient is unique in that it represents a case of rapid change from one disorder to the other. In a time frame of 3 months, the same location on the scalp demonstrated remission of psoriasis and induction of AA, and later reappearance of psoriasis accompanied by hair growth, representing a rapid change from Th-17 to Th-1 and back to Th-17 response.