Cytomegalovirus (CMV) in gastrointestinal mucosal biopsies: should a pathologist perform CMV immunohistochemistry if the clinician requests it?

Cytomegalovirus (CMV) causes clinically significant gastrointestinal (GI) injury. CMV inclusions can be identified on routine hematoxylin and eosin (H&E) stain, but immunohistochemistry (IHC) is also available for identifying CMV in tissue. The advent of accountable care organization models of care bring into question whether it is cost-effective for immunohistochemistry to be performed upfront at the request of clinicians and whether the quality of viral detection is compromised when the diagnosis of CMV is predicated on histologic review. In this study, a retrospective review of GI biopsies with CMV evaluations was performed. There were 449 cases with clinical requests to rule out CMV and 238 CMV analyses initiated by the pathologist without a clinical request. Among the cases that included a clinician's request, 37 had CMV detected. Immunostaining was performed on 26 cases, while a diagnosis based on readily identifiable viral inclusions on H&E-stained slides was made in 11. Among pathologist-initiated work-ups, 15 were CMV+, 3 of which had inclusions identified by H&E only. Among 38 CMV cases for which IHC had been performed, 27 had overt viral inclusions obvious on H&E. Seventy-two cases revealed uninflamed GI mucosa, and although a clinical concern about CMV infection was present, a CMV IHC work-up was not initially performed; all were negative for CMV by IHC and H&E. Clinical suspicion for CMV has a high yield for CMV detection, but "upfront" testing is likely unnecessary. Careful histopathologic review by a pathologist remains critical in the efficient and cost-effective detection of CMV.