The histologic distinction between cytomegalovirus (CMV) infection and
graft-versus-host disease (GVHD) in the colon in bone marrow transpla
ntation (BMT) patients relies heavily on the identification of viral i
nclusions, because the morphologic features of these two diseases are
otherwise similar. The aim of this study was to assess (1) the prevale
nce of colonic CMV infection in BMT patients with the use of DNA in si
tu hybridization (ISH); and (2) the sensitivity and specificity of lig
ht microscopy in establishing a diagnosis of CMV infection in the colo
n of these patients, Fifty-five colonic mucosal biopsy samples from 50
consecutive allogeneic BMT patients with diarrhea were evaluated hist
ologically for the presence of typical or atypical (suspicious, but no
t 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 a
nalysis revealed only one patient with morphologically typical CMV inc
lusions. Four other cases contained an isolated atypical mesenchymal c
ell with features considered suspicious, but not diagnostic, for CMV i
nclusions, All of these five cases exhibited histologic features that
were otherwise indistinguishable from GVHD grades 1 to 2. The single c
ase 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 meth
od 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 co
litis in our BMT population.