The incidence of allergic contact dermatitis in patients with psoriasis vulgaris

Abstract

Background: Contact dermatitis is said to be rare in psoriasis patients, possibly because of accelerated epidermal turnover, the isomorphic (Koebner) response, and lymphocyte functional alterations. Objective: To identify contact allergy in patients with psoriasis. Methods: A written questionnaire was completed by 100 patients with psoriasis about contact history, flare factors for psoriasis, topical skin care, medications, and occupational/hobby exposures. Of these patients, 20 agreed to be patch tested with a standard screening series (Hermal) and a 20-item psoriasis patch-test series that included ingredients that might be found in topical psoriasis products. Results: Of the 100 patients, eight suspected a topical medication caused a reaction that worsened their psoriasis, 29 gave a history of atopy, 11 reported reactions to metal jewelry, and 29 reported an allergy to poison ivy. Patch-test results identified four of the 20 patients with six positive patch tests to the materials tested: three of the six positive tests were interpreted as relevant to the patient's psoriasis (coal tar, ethylenediamine and dithranol), two patients tested positive to nickel and one to thimerosal. Five patients had irritant reactions to dithranol. Conclusions: In this small study, 20% of self-selected psoriasis patients had positive allergic reactions on patch testing. A screening contact and atopic history in psoriasis patients may help to identify a subset of patients who could benefit from a search for more relevant contact allergens with patch test evaluation. This could improve treatment strategies and possibly reduce disability.