Medical Mystery of the Week

       You are asked to make a diagnosis in a 25-year-old woman who had the onset of a "rash" involving her lips and buccal mucosa, palms of both hands, and, to a lesser extent, her trunk, at the age of 20. She was treated with an antiviral (for possible reaction to a herpes simplex virus) and NSAIDs with gradual resolution of the dermopathy. She subsequently had three relapses (∼1 per year) with the last relapse occurring at the age of 24 shortly after she was diagnosed as having a mild case of COVID-19 (see photos below).
      What is your diagnosis, what test(s) would you order to confirm your suspicions, and what treatment, if any, do you recommend?
      DIAGNOSIS: Erthema multiforme (EM).
      EM is an immune-mediated reaction that involves the skin and sometimes the mucosa. Classically described as "target lesions", the lesions can be isolated, recurrent, or persistent. Most commonly, they occur on the extremities (especially on extensor surfaces) and spread centripetally. Infections, particularly with the herpes simplex virus (HSV) and Mycoplasma pneumoniae, and medications constitute the most frequent causes of EM, although it has also been associated with immunizations and autoimmune diseases. Treatment is nonspecific and may include topical steroids, antihistamines, and anti-HSV medications. Severe mucosal EM may require hospitalization.
      The diagnosis of EM in the presented case was confirmed by biopsy. The cause was never identified, although she is restricted from taking NSAIDs.
      

Typical "target" lesions on the palms and fingers (extensor surfaces) of the hands (top image). Erosive mucosal lesions and inflammatory edema of the lips (bottom image).

Citation: Trayes K.P., Love G., Studdiford J.S. Erythema multiforme: recognition and management. Am Fam Physician. 2019; 100(2):82-88.