CT found that when combined with the clinical scenario all were diagnostic, showing ascites
and colonic wall thickening or massive dilatation. Eleven patients had right-sided colitis, while
9 had left-sided colitis and 19 had pancolitis (40). Barium enemas are not recommended due to
the risk of perforation (44).
Visualization of pseudomembranes during endoscopy in the right clinical scenario is
diagnostic of CDI. Even though there are several other causes of PMC they are exceedingly
rare (25). Endoscopy is preferred over sigmoidoscopy since approximately one-third of the
patients have involvement of the right colon only. Pseudomembranes found in the colonic
mucosa are raised yellow plaques 2 to 10 mm in diameter, frequently with normal intervening
mucosa (Fig. 1) (3). Other gross findings include bowel wall edema, erythema, friability, and
inflammation. Histologically, a pseudomembrane is composed of sloughed mucus with rare
inflammatory cells, fibrin, and cellular debris. The appearance on a biopsy is that of acute
nonspecific inflammatory changes with or without crypt abscesses and eruptive “volcano”
lesions (45).
In 50% of the cases, however, pseudomembranes are not present, making endoscopy a
relatively insensitive test (43). Further, endoscopy should be avoided in patients with severe
disease with colonic dilatation due to the risk of perforation.Aboratory Testing
Analysis of stool samples is the standard diagnostic test for CDI. Laboratory testing for
C. difficileis recommended for all adults and for children >1 year of age who have otherwise
unexplained diarrhea associated with antibiotic use (25).Assays Detecting the Organism- Stool cultureis rarely used for routine diagnosis ofC. difficilein the United States due
to its long turnaround time 24 to 48 hours, and it is labor intensive and not specific
for in vivo toxin production (25). Stool cultures are highly sensitive but the specificity
is low because non-disease-causing, non-toxigenic strains of the bacterium would
also grow naturally on media. The culture must be accompanied by tissue culture
cytotoxin assay or enzyme immunoassay to identify toxigenic strains. As a result,
diagnosis may be delayed by three to four days. However, since stool cultures allow
for molecular typing it is an essential tool for monitoring molecular epidemiology
and antibiotic susceptibility. - The common-antigen test, also known as the glutamate dehydrogenase (GDH) test, is
an EIA for the GDH enzyme.C. difficileconstitutively produces GDH in easily
detectable levels and carries a sensitivity of 96% to 100% (46). However, a positive
Figure 1 Typical endoscopic findings in pseudomembranous colitis; widely disseminated, punctate yellow
plaques with normal intervening mucosa.
278 Hjalmarson and Gorbach