Are there cytopathic features associated with cytomegalovirus infection predictive of resistance to antiviral therapy?

Recent awareness of the broader spectrum of morphologic changes induced by cytomegalovirus (CMV) infection prompted us to investigate whether the concurrent introduction of effective antiviral therapy is in some way related to the appearance of atypical cytopathic features. These changes may be easily misinterpreted on histologic examination as reactive or degenerative. In addition, since resistant strain to antiviral therapy has emerged and its demonstration is a laborious process performed in highly specialized laboratories, it is important to determine if resistance to antiviral drugs can be predicted from the microscopic examination of infected tissues. The population consisted of seven immunosuppressed patients with documented CMV infection from which 18 tissue samples were obtained at autopsy or endoscopically. Antiviral susceptibility to ganciclovir was determined by plaque reduction assay and/or a DNA-DNA hybridization method. Eleven tissue specimens from patients harboring resistant strains were compared with seven specimens from patients infected with sensitive strains. Cytopathic changes were classified as typical or atypical according to previously published criteria. Of the 18 biopsy specimens, the cytopathic changes were distributed as follows: typical 1, typical and atypical 5, and atypical 12. Atypical inclusions were found in 10 of 11 and 7 of 7 sensitive and resistant cases, respectively. In conclusion, there are no specific morphologic features in CMV-infected tissues of patients with infections caused by ganciclovir resistant strains.