Pseudolymphomatous reaction to varicella zoster virus vaccination: role of viral in situ hybridization.

Herpes zoster (shingles) is the result of a reactivation of the varicella zoster virus (VZV). Many adults obtain a VZV vaccine in order to prevent zoster. Non-specific injection site reactions and generalized herpes eruptions have been reported to occur, especially in immunocompromised patients. However, these are most often anatomically generalized reactions and histopathologically resemble typical herpes infections. We report a 61-year-old female on immunosuppressant medications for rheumatoid arthritis who presented with a subcutaneous nodule at the site of a recent herpes zoster vaccination. Histopathological examination revealed a dense nodular and interstitial mononuclear infiltrate throughout the mid and deep dermis with extension into the superficial subcutaneous fat. Immunohistochemical staining revealed an admixture of T-cells and B-cells, with a predominance of T-cells. These findings are consistent with a pseudolymphoma (PL), a reactive inflammatory disorder that can resemble cutaneous lymphoma and has rarely been described in herpes infections and post-herpetic scars. In situ hybridization studies for VZV were performed and highlighted occasional deep fibroblasts with nuclear positivity for VZV DNA. A review of post-vaccination reactions and herpes-related PL is discussed with emphasis on using in situ hybridization in establishing the diagnosis.