Eosinophils are surprisingly common in biopsy specimens of cutaneous herpes simplex virus and varicella zoster virus infections: Results of a comprehensive histopathologic and clinical appraisal

Background: While usually straightforward, diagnostic features of cutaneous herpes simplex virus and varicella zoster virus infection (HSV/VZV) are not always present in biopsy specimens. Although intuitively the presence of eosinophils may lead the pathologist away from the diagnosis of cutaneous HSV/VZV infection, in our practice we have noted that eosinophils are often encountered in diagnostic specimens. Methods: To deduce the frequency with which the inflammatory response accompanying cutaneous HSV/VZV infection includes significant numbers of eosinophils, we performed a retrospective review. We included 159 specimens from our database, diagnosed between 2009 and 2017. We determined the number of eosinophils in 10 high-power fields and noted additional histologic factors including presence of follicular involvement, ulceration, and pseudolymphomatous change. Results: Of all included cases, 63% had 0-1 eosinophils, 24% had 2-10 eosinophils, and 13% had more than 10 eosinophils. Statistical analysis did not reveal a significant association between any demographic or histologic features examined and the presence of increased eosinophils. Conclusions: In this study, more than one-third of biopsy specimens diagnostic of cutaneous HSV/VZV infection had a prominent number of eosinophils. The detection of eosinophils should not be unexpected and should not lessen diagnostic suspicion for cutaneous HSV/VZV infection.