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Most of the time, ultraviolet radiation improves psoriasis, and it can sometimes produce durable remissions. From time to time, however, psoriasis worsens after skin exposure to sunlight. A cohort of 20 patients with this “photosensitive psoriasis” had several characteristics in common: overwhelming female predominance (19 females), young age at onset (mean age, 11 years; range, 2–24 years), family history of psoriasis (13 patients), and the genotype HLA-Cw*0602 (16 patients).
In these patients, plaques occurred predominately on sun-exposed areas of skin, and disease was worse in summer months. To test for photosensitivity, a subgroup of 10 patients received suberythemal doses of broadband UVB on 3 consecutive days. Biopsies were taken from …