Contact allergy to calcipotriol does exist. Report of an unequivocal case and review of the literature

A 64-year-old woman developed an itchy papulovesicular dermatitis at the periphery of psoriatic plaques on the lower legs after the daily application of calcipotriol ointment (Psorcutan® 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 calcipotriol in a concentration series (2.0, 10.0 and 50.0 μg/ml in isopropyl alcohol). A repeated open application test (ROAT) on the forearms showed a vesicular dermatitis after 4 days on the side that received the calcipotriol ointment, whereas the control with the placebo ointment remained completely negative. Histologic examination of the ++ patch test reaction was in line with the picture of contact allergy. Retesting after 6 months confirmed the hypersensitivity, with a positive reaction even at 0.4 μg/ml. For comparison, 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. Based 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 testing, a concentration of 2 μg/ml in isopropyl alcohol is the most suitable. If the reaction is only weakly positive and not reproducible after some time, it might be of the irritant type. In unclear cases, a ROAT should be performed. A severe papulovesicular dermatitis within 1 week will confirm the presence of contact allergy.