Psoriasiform intradermal test reaction to ABPC in a patient with psoriasis and ABPC allergy

We experienced a case of psoriasis with ABPC allergy which showed a psoriasiform intradermal test reaction to ABPC. A 22-year-old man with a history of psoriasis since the age of 17 was admitted to our department because he developed erythrodermic psoriasis after oral administration of ABPC. About 1 year later, he again developed erythroderma after administration of ABPC. Intradermal testing with 2% ABPC was performed. We found infiltrating erythema at day 2, followed by a gradually increasing psoriasiform reaction at 6 days on the site of ABPC skin test. We examined the infiltrating cells in the skin test reaction immunohistochemically. Most of the infiltrating cells in the dermis were activated helper/DTH-type T cells. Among the infiltrating cells in the epidermis, we observed more cytotoxic/suppressor-type T cells than helper/DTH-type T cells. A possible role of a DH reaction to ABPC in inducing the psoriatic lesion is discussed in relation to the pathomechanisms of psoriasis.