The response of uninvolved skin of patients with psoriasis to single and repeated applications of dithranol cream: an immunohistochemical assessment.

Dithranol is one of the most effective topical treatments for patients with psoriasis. The well-known irritation is a serious limitation. In an earlier study we investigated the inflammatory response to single and repeated applications with dithranol 2% cream in skin from healthy volunteers. In the present study, we assessed the clinical and cell-biological response of single and repeated challenges with dithranol 2% cream in uninvolved skin of patients with psoriasis. A striking difference between the two studies is the late phase in the single-challenge group after 8 days, showing a longer-lasting response in the uninvolved skin compared to normal skin with respect to proliferation and inflammation markers. A controlled and synchronised irritation by dithranol might induce anti-inflammatory processes and as such constitute an antipsoriatic principle. It is attractive to speculate that in psoriasis the induction of anti-inflammatory responses is defective. Following repeated applications of dithranol, a more uniform course of proliferation, differentiation and inflammation markers was observed in the uninvolved psoriatic skin as compared to the skin of healthy volunteers. Again a defect in the induction of anti-inflammatory responses might account for this event. In view of these differences between normal skin and psoriatic uninvolved skin, it may be advisable to use the uninvolved skin of patients with psoriasis in further studies on the interference between dithranol irritancy and various anti-inflammatory agents.