Autoimmune progesterone dermatitis. Case report with histologic overlap of erythema multiforme and urticaria

Background Autoimmune progesterone dermatitis is a rare eruption that recurs monthly as progesterone levels peak during the menstrual cycle. Clinical and histologic features are variable, and the eruption is thought to represent a hypersensitivity response to endogenous progesterone. Methods We present the case of a 38-year-old woman with a pruritic intermittent facial eruption of 18 months' duration that recurred predictably in the days surrounding menses. Results The histology showed interface dermatitis with features of both erythema multiforme and urticaria. Intradermal injection of medroxyprogesterone acetate was positive. Her symptoms responded to antihistamine therapy. Conclusion This unusual case is particularly distinctive both in terms of the histologic findings and the response to therapy.