Apoptosis, Crypt Dropout, and Equivocal Immunohistochemical Staining May Indicate Cytomegalovirus Infection in Inflammatory Bowel Disease Patients.

Cytomegalovirus (CMV) colitis superimposed on inflammatory bowel disease (IBD) can be challenging to diagnose. This study aimed to determine what histologic clues and immunohistochemistry (IHC) utilization practices, if any, can help diagnose CMV superinfection in IBD. Colon biopsies were reviewed from all patients with CMV colitis with and without IBD between 2010 and 2021 at one institution, along with a separate cohort of IBD patients with negative CMV IHC. Biopsies were assessed for histologic features of activity and chronicity, phlebitis, fibrin thrombi, basal crypt apoptosis, CMV viral cytopathic effect (VCE), and CMV IHC positivity. Features between groups were compared, with statistical significance set at P-value <0.05. The study included 251 biopsies from 143 cases (21 CMV-only, 44 CMV+IBD, 78 IBD-only). Compared with the IBD-only group, the CMV+IBD group was more likely to show apoptotic bodies (83% vs. 64%, P=0.035) and crypt dropout (75% vs. 55%, P=0.045). CMV was detected by IHC in 18 CMV+IBD cases without VCE on hematoxylin and eosin (41%). In the 23 CMV+IBD cases where IHC was performed on all concurrent biopsies, IHC was positive in at least 1 biopsy in 22 cases. Six individual CMV+IBD biopsies with no VCE on hematoxylin and eosin demonstrated equivocal IHC staining. Of these, 5 had evidence of CMV infection. IBD patients with superimposed CMV infection are more likely to demonstrate apoptotic bodies and crypt dropout compared with their noninfected counterparts. Equivocal IHC staining for CMV may indicate true infection in IBD patients, and staining multiple biopsies from the same accession can improve CMV detection.