Immunohistochemistry Is Rarely Justified for the Diagnosis of Viral Infections

Objectives: To determine the utility of immunohistochemistry (IHC) for the diagnosis of viral infections in surgical pathology specimens lacking characteristic viral cytopathic effects. Methods: Five years of cases at an academic medical center were reviewed for the use of IHC to detect cytomegalovirus (CMV), herpes simplex virus 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), adenovirus, or polyomavirus (ie, BK or JC). Results: In total, 1,636 viral IHC stains were ordered on 1,099 specimens from 957 cases. Altogether, 134 (8.2%) stains were positive, including 59 (7.9%) of 749 for CMV, 34 (8.9%) of 384 for HSV-1 and HSV-2, 16 (11.5%) of 139 for VZV, three (1.4%) of 210 for adenovirus, and 22 (14.3%) of 154 for polyomavirus. In 101 (75.4%) of 134 cases, viral cytopathic effect (VCPE) was readily identifiable on H& E slides. No significant changes in clinical care occurred in any of the cases without definitive VCPE that had positive staining cells on IHC. Conclusions: These findings suggest that IHC for viral infections without a high degree of clinical or histologic suspicion is unnecessary in most cases.