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The Woronoff ring in psoriasis

A 42-year-old man with a 21-year history of chronic plaque psoriasis presented with a flare of his psoriasis (Fig. 1). He had been using topical dithranol only to his limbs. Examination showed typical psoriasis on the trunk and extensor surfaces of the limbs. A florid example of a rarely reported sign, the Woronoff ring, was noted on his trunk (Fig. 2). Psoriasis affects 1–2% of caucasians. In addition to well-demarcated erythematous plaques with silvery scaling, commonly recognized physical signs include nail pitting, onycholysis, subungual hyperkeratosis and the Koebner phenomenon. An under-recognized sign is the Woronoff ring. Little reference is made to this sign in standard textbooks, with few published clinical images. The ring represents a halo of non-reddened skin surrounding an erythematous plaque. This sign occurs after ultraviolet radiation or topical corticosteroid treatment for psoriasis. The pathogenesis is not well understood but may result from inhibition of prostaglandin synthesis. The Woronoff ring can occur in untreated psoriasis, as on the trunk in our subject, and it may be that certain anti-inflammatory mediators are present in the halo surrounding the psoriatic plaque.