The influence of a topical corticosteroid on short-contact high-dose dithranol therapy

Background Dithranol (anthralin) has been known to be effective in the trea tment of psoriasis for more than 80 years. However, perilesional and uninvo lved skin often show irritation during dithranol treatment, which limits it s use. As the relapse rate of psoriasis is worsened by adding corticosteroi ds to a dithranol regimen, the use of topical corticosteroids to reduce dit hranol irritation is controversial. Objectives The aim of the present study was to investigate the clinical and cell biological effect of clobetasol-17-propionate 0.05% ointment on dithr anol-treated lesional and perilesional skin. Methods For 17 consecutive days, 2% dithranol cream was applied on two test sites. A third site was left untreated on all participating patients (n = 8). All sites consisted of a psoriasis lesion as well as a 3-cm zone of per ilesional skin localized on the back. After 1 h, the cream was washed off, and subsequently one of the dithranol-treated sites was treated once a day with clobetasol-17-propionate 0.05% ointment. The second site was treated o nce daily with the vehicle. On day 17, punch biopsies were taken from all t hree lesions and from the perilesional zone of all test sites in order to p erform an immunohistochemical investigation, using markers to assess prolif eration, differentiation and inflammation. Results The SUM score (erythema + induration + scaling) of the lesion treat ed with dithranol/clobetasol showed a pronounced reduction, which was signi ficantly greater than the SUM score of the lesion treated with dithranol/ve hicle. However, the scores of both sites were equal by 6 weeks of follow-up . Comparing the two treated lesions, we observed a lower number of cycling epidermal cells in the dithranol/clobetasol lesion and a significantly lowe r perivascular dermal score of T lymphocytes. Comparing the perilesional sk in of the two treated sites we observed less cycling epidermal cells in the dithranol/clobetasol-treated site. Regarding perilesional differentiation, the interpapillary involucrin expression was higher in the dithranol/clobe tasol-treated site. With respect to perilesional inflammation the expressio n of dermal polymorphonuclear leucocytes, monocytes, macrophages and T lymp hocytes in the dermal infiltrate were significantly lower in the dithranol/ clobetasol-treated site. Conclusions The addition of clobetasol-17-propionate enhanced the antipsori atic efficacy of dithranol by interfering with T-cell accumulation and epid ermal proliferation. The addition of a corticosteroid reduced perilesional dithranol inflammation at the cellular level, although clinically detectabl e dithranol erythema was not reduced.