CYTOMEGALOVIRUS INFECTION IN THE COLON OF BONE MARROW TRANSPLANTATION PATIENTS

: The histologic distinction between cytomegalovirus (CMV) infection and graft-versus-host disease (GVHD) in the colon in bone marrow transplantation (BMT) patients relies heavily on the identification of viral inclusions, because the morphologic features of these two diseases are otherwise similar. The aim of this study was to assess (1) the prevalence of colonic CMV infection in BMT patients with the use of DNA in situ hybridization (ISH); and (2) the sensitivity and specificity of light microscopy in establishing a diagnosis of CMV infection in the colon of these patients. Fifty-five colonic mucosal biopsy samples from 50 consecutive allogeneic BMT patients with diarrhea were evaluated histologically for the presence of typical or atypical (suspicious, but not diagnostic) CMV inclusions and, if negative, for the grade of GVHD. CMV DNA ISH analysis was performed on all of the biopsy specimens and was correlated with the histologic and clinical findings. Histologic analysis revealed only one patient with morphologically typical CMV inclusions. Four other cases contained an isolated atypical mesenchymal cell with features considered suspicious, but not diagnostic, for CMV inclusions. All of these five cases exhibited histologic features that were otherwise indistinguishable from GVHD grades 1 to 2. The single case that was histologically positive for CMV was confirmed by DNA ISH. Of the four histologically atypical cases, only one was confirmed to be CMV positive by DNA ISH. Of the remaining 45 patients, 35 had GVHD, 1 had pseudomembranous colitis, 1 had ischemic colitis, and 8 had no abnormalities found. Light microscopic examination is a sensitive method of screening for CMV infection in the colon of BMT patients but is less specific than DNA ISH. CMV infection is an infrequent cause of colitis in our BMT population.