Recurrent erythema multiforme triggered by progesterone sensitivity

Determining the underlying etiology of recurrent erythema multiforme (EM) can be a difficult endeavor. Although infection with herpes simplex virus (HSV) has been implicated in some cases, the precise trigger of a given patient's recurrent EM often remains elusive. We discuss the case of a woman with a recurrent blistering eruption that was clinically and histopathologically consistent with EM. An investigation into the etiology of the patient's EM suggested that HSV was not the causative factor but instead pointed toward a hormonal influence that we interpret as autoimmune progesterone dermatitis (APD). This case is presented to highlight the importance of considering hormonal triggers in women with recurrent EM that consistently flares during the luteal phase of the menstrual cycle, the point at which serum progesterone levels peak. A brief review of the literature regarding the diagnosis, histopathology, etiology and treatment of APD is further provided.