Diagnosis of Ulcerative Colitis
The diagnosis of ulcerative colitis is clinical and based on the combination of the clinical presentation, mucosal appearance at endoscopy or radiography, and histologic findings in mucosal biopsies.
The laboratory features of
ulcerative colitis are nonspecific and reflect the severity
of inflammation (i.e., increased erythrocyte sedimentation rate, leukocytosis
with a “left shift”), complications of diarrhea (hypokalemia,
alkalosis, other electrolyte disturbances), or complications of mucosal
exudation (anemia from chronic blood loss and iron deficiency or
hypoalbuminemia from protein exudation).
Recently, serologic tests have been evaluated for sensitivity and
specificity in IBD. In
ulcerative colitis there is a unique perinuclear antineutrophil
cytoplasmic antibody (pANCA) that is present in approx 60% of confirmed
cases. The specificity of pANCA is only approx 80% for UC. In
contrast anti-Saccharomyces cerevisiae antibodies (ASCA) are more
common in patients with CD. The combination of a positive pANCA
Chapter 5 / Diagnosis of IBD 81
and a negative ASCA supports, but does not confirm, the clinical diagnosis
of UC. However, because of their limited sensitivity and specificity,
these serologic tests do not generally alter the clinical impression as
to the presence or absence of IBD.
A hallmark of active colitis is the presence of fecal leukocytes on wet
mount. Additional stool studies are necessary to rule out infectious colitis
due to bacteria [including Clostridium difficile and enterohemorrhagic
E. coli (E.coli O157:H7)] or parasites (especially amebiasis).
Plain abdominal radiography is mostly useful in excluding perforation
or megacolon. Rarely, CT scans are used to rule out an abdominal
abscess. However, for the most part, while air-contrast barium enemas
can be used to confirm
mucosal inflammation in UC, these studies have
been supplanted by endoscopic examinations with flexible sigmoidoscopes
or colonoscopes. Colonoscopy, including examination into the
terminal ileum, is eventually performed in all patients to assess the
extent of involvement, obtain biopsies and rule out ileitis. However, in
the acute setting, flexible sigmoidoscopy is sufficient to assess severity
and extent beyond proctosigmoiditis, and to obtain biopsies. Careful
sigmoidoscopy is safe in patients with severe disease. The inflammatory
changes are nearly always more severe distally, and range from
mild (erythema, loss of vascular pattern and granularity), to moderate
(friability, petechiae, nonconfluent ulcerations), or severe (confluent
ulcerations, mucopus, spontaneous hemorrhage). Additional findings
may include the presence of postinflammatory pseudopolyps.
Mucosal biopsies reflect the diffuse, continuous, superficial inflammation
with acute and chronic inflammatory cells, cryptitis, and crypt
abscesses. These changes are nonspecific and may be difficult to distinguish
from changes secondary to infection. In contrast, distortion of
intestinal crypts (irregular, elongated, or branched crypts) is a hallmark
of idiopathic IBD and persists, not only in
active
ulcerative colitis (or CD) but also
in quiescent UC. The diffuse, superficial mucosal changes in UC differentiate
it from CD, where focal and transmural inflammation is more
common. The colonic mucosa proximal to the demarcating margin of
colitis is normal.