Idiopathic erythema multiforme: Evidence of underlying Janus kinase–signal transducer and activator of transcription activation and successful treatment with tofacitinib

EM: erythema multiforme HSV: herpes simplex virus JAK-STAT: Janus kinaseesignal transducer and activator of transcription TRPS: tricho-rhino-phalangeal syndrome INTRODUCTION Erythema multiforme (EM) is an acute, typically self-limited mucocutaneous eruption characterized by distinctive target lesions. In a subset of patients, EM has a more chronic course, with recurrent episodes or even persistent disease. In some of these patients, EM is related to chronic infections, most commonly herpes simplex virus (HSV), and will respond to antiviral therapy. However, in up to 58% of patients, the etiology is unknown, and in these cases treatment is often difficult.