Herpes simplex virus-induced plasmacytic atypia

The clinical and histopathological features of cutaneous herpes simplex virus (HSV) infection have been well described. Genital herpetic infections are largely induced by HSV type 2, but 30% of cases can be caused by HSV type 1. Immunocompromised patients are known to exhibit atypical patterns of clinical presentation with variable lesion morphology and anatomic location. A subset of patients may show morphology such as nodules or verrucous lesions. Analogously, some biopsy specimens may show unusual microscopical features, such as a lack of keratinocyte cytopathology, lymphocyte infiltration or vasculopathic changes that are expected irrespective of the patient's immune status. We present the case of a patient carrying a previous diagnosis of pemphigus vulgaris, status posttreatment with methotrexate and prednisone, who developed a perineal ulcer exhibiting significant numbers of plasma cells, many of which were cytologically atypical. This morphology was suggestive of a hematopoietic malignancy. Immunoperoxidase staining for HSV decorated a focal collection of keratinocytes that lacked appreciable viral changes expected of HSV infection.