The effects of topical corticosteroids and a coal tar preparation on dithranol-induced irritation in patients with psoriasis

Dithranol has been a mainstay in the treatment of psoriasis for more than 80 years. Although a safe approach, the irritation of the clinically uninvolved perilesional skin remains a major limitation of this treatment. Corticosteroids and coal tar solution have an anti-inflammatory potential. The aim of the present study was to investigate the clinical and cell-biological effects of two topical corticosteroids and a coal tar preparation on dithranol-irritated skin. During 4 consecutive days, 2% dithranol cream was applied to six uninvolved skin sites (3 cm in diameter) on the lower back of 9 patients with psoriasis. Dithranol was left on the skin for 1 h, subsequently removed with water and soap and the skin was dried with a towel. Subsequently, SITE 1 was treated with 0.05% clobetasol-17-propionate ointment (CP), SITE 2 with unguentum cetomacrogolis (vehicle 1), SITE 3 with 0.005% fluticasonpropionate ointment (FP), SITE 4 with 10% coal tar solution in lanettewax cream (CTS), SITE 5 was left untreated (control) and SITE 6 was treated with lanettewax cream (vehicle 2). Erythema, oedema and vesicle formation was scored every day. On day 5, punch biopsies were taken from the six sites. The expression of epidermal proliferation, differentiation and inflammation markers and the clinical irritation scores indicate that the application of a high potency corticosteroid (CP) is the best approach to minimise dithranol irritation, whereas CTS had virtually no effect on dithranol irritation during this 4-day experimental model.