Frequency of patch-test positivity in patients with psoriasis: a prospective controlled study.

Current information on the incidence of patch-test positivity and the spectrum of allergens in psoriatics is conflicting. We compared the rates of patch-test positivity to common allergens and topical medicaments in 200 patients suffering from chronic plaque psoriasis (group I) with 51 patients with other non-allergic skin complaints (group II) and 54 patients suspected of having allergic contact dermatitis (group III). Positive patch-test results to one or more allergens were detected in 21.6% of patients in group I, 23.5% in group II and 50.0% in group III. Psoriatics with > or = 5 years old disease had a higher rate of patch-test positivity than those with shorter disease duration (p<0.01). The site of lesions showed no correlation with patch-test positivity. The commonest allergens showing positivity in group I were dithranol (6.5%), nickel (6%), fragrance mix (5%), neomycin (2%) and nitrofurazone (2%). In spite of the comparable rates of patch-test positivity in psoriatics and general dermatology outpatients, the predominance of sensitivity to topical medicaments and fragrance in the former group was striking. A separate psoriasis series focusing on topical agents may give more accurate information on this subject.