Recent studies examining immunohistochemical staining of colorectal biopsies for cytomegalovirus (CMV) reported that some cases showed only occasional small positive nuclei that were called equivocal for CMV.
To determine the extent and clinical significance of equivocal CMV staining in colorectal biopsies.
Two-hundred twenty-one consecutive cases of colon and rectal biopsies that were stained for CMV by immunohistochemistry were retrieved from our files and reviewed. Staining results were recorded as negative, unequivocal, or equivocal. Results were correlated with clinicopathologic data, results of polymerase chain reaction studies for CMV, and treatment history.
Fifty-two cases (24% of all tested, 63% of positive cases) showed equivocal staining for CMV, and of these, 41 had follow-up information. Polymerase chain reaction for CMV was performed largely on blood samples and was not found to be sensitive for the detections of CMV proctocolitis. Of 25 patients who received antiviral treatment, 21 (84%) had complete resolution of symptoms, compared with 8 of 16 (50%) who did not receive antivirals ( = .02). There was no statistically significant difference in response to antiviral drugs in patients with equivocal and unequivocal CMV staining ( = .17).
Equivocal CMV staining likely represents true CMV proctocolitis. Prospective studies are needed to confirm these findings.