Diagnosis of herpes simplex virus-induced erythema multiforme confounded by previous infection with Mycoplasma pneumonia.

Erythema multiforme (EM) is an immune-mediated hypersensitivity reaction often related to viral infection or medications. Infection-induced EM is typically self-limited and commonly caused by herpes simplex virus (HSV) or Mycoplasma pneumoniae (MP); recurrent EM is almost always associated with HSV. We present a concise overview of diagnostic techniques for HSV and MP, as repeatedly elevated MP titers in our case led to a delayed diagnosis of HSV-induced EM.