Contact allergy to calcipotriol does exist - Report of an unequivocal caseand review of the literature

A 64-year-old woman developed an itchy papulovesicular dermatitis at the pe riphery of psoriatic plaques on the lower legs after the daily application of calcipotriol ointment (Psorcutan(R) Salbe) for 2 weeks. She had used the same ointment for 4 weeks 6 months before. Patch testing revealed strongly positive reactions to the marketed product and to the active ingredient ca lcipotriol in a concentration series (2.0, 10.0 and 50.0 mu g/ml in isoprop yl alcohol). A repeated open application test (ROAT) on the forearms showed a vesicular dermatitis after 4 days on the side that received the calcipot riol ointment, whereas the control with the placebo ointment remained compl etely negative. Histologic examination of the ++ patch test reaction was in line with the picture of contact allergy. Retesting after 6 months cofirme d the hypersensitivity, with a positive reaction even at 0.4 mu g/ml. For c omparison, the ROAT with calcipotriol ointment was performed for 2 weeks on both forearms of 15 volunteers never exposed to calcipotriol before. Only 2 subjects developed a slight reaction on days 5 and 11, respectively. Base d on this case and on previous reports in the literature, calcipotriol must now be regarded as both a contact allergen and an irritant. For patch test ing, a concentration of 2 mu g/ml in isopropyl alcohol is the most suitable . If the reaction is only weakly positive and not reproducible after some t ime, it might be of the irritant type. In unclear cases, a ROAT should be p erformed. A severe papulovesicular dermatitis within 1 week will confirm th e presence of contact allergy.