Focal active colitis (FAC) is a histologic pattern of injury, not a specific
diagnosis. From a morphologic standpoint, FAC is defined either as a single
focus of neutrophilic crypt injury (cryptitis) or as multiple separate
foci of cryptitis occurring in different pieces of tissue within the same
biopsy specimen. The crypt injury may be accompanied by increased mononuclear
cells in the lamina propria; however, no features of chronic injury, such
as architectural distortion, basal plasmacytosis, or Paneth cell metaplasia
So what does FAC mean clinically? Well, it depends on the clinical and
endoscopic findings. In an asymptomatic patient undergoing a routine screening
colonoscopy, the finding of FAC is most likely related to bowel preparation
and therefore of no clinical significance. Oral sodium phosphate preparations
are reported to cause focal active colitis in up to 3% of patients. In
this scenario, the finding of FAC can typically be safely ignored.
In symptomatic patients, studies have shown the most common underlying
clinical condition associated with FAC was found to be infection, including
cases of so-called acute “selflimited colitis” diarrheal illness
in which no infectious organism is ever found, as well as cases in which
a specific etiologic agent is identified by laboratory methods. Most infections
showing only FAC represent either mild or resolving infectious colitis.
In the absence of an infectious etiology, what else can cause focal active
colitis? The same studies implicated ischemia as the cause of a focal
active colitis pattern of injury in 5-10% of cases. Non-steroidal anti-inflammatory
drugs (NSAIDs) and other medications are increasingly recognized causative
agents in the setting of focal active colitis. Diverticular disease-associated
segmental colitis comprises a spectrum of morphologic changes, including
FAC, and this fact emphasizes how important endoscopic-pathologic correlation
can be in arriving at a diagnosis: if the pathologist is aware that the
biopsy was taken from an area affected by diverticular disease, then it
can be suggested with a high degree of certainty that the focal active
colitis is related to underlying diverticula.
How does focal active colitis relate to idiopathic inflammatory bowel disease
(IBD)? Certainly, the finding of FAC would not be unusual in a patient
with a known history of IBD, but what if the patient has no known history
of IBD? In one study of non-IBD patients with focal active colitis as
the only histopathologic finding, no adult patients developed IBD; however,
in another study, 13% of adult patients were later diagnosed with Crohn’s
disease after a histologic finding of FAC. (Volk, Mod Pathol 1998; 11:789-794)
It is important to note, though, that patients in the latter study also
had clinical and endoscopic findings of Crohn’s disease. Therefore,
it is reasonable to conclude that an isolated pathologic finding of FAC
in adult patients is rarely a harbinger of incipient IBD. Children represent
an important exception: in one study, 27.6% of children with an isolated
finding of focal active colitis were later diagnosed with Crohn’s
disease (Bihlmeyer, Diagnostic pathology, gastrointestinal, Salt Lake
City: Amirsys; 2010, 5-68—5-69.). These data show that FAC must
be interpreted differently in younger patients.
Unfortunately, in some cases of focal active colitis, the underlying etiology
may never be determined. Such “incidental FAC” cases may comprise
up to 25% of cases, underscoring the importance of endoscopic-pathologic
correlation so that a specific diagnosis can at least be suggested in
as many cases as possible.
Bihlmeyer, SK: Focal active colitis. In: Greenson JK, ed. Diagnostic pathology,
gastrointestinal, Salt Lake City: Amirsys; 2010, 5-68—5-69.
Greenson JK, Odze RD: Inflammatory disorders of the large intestine. In
Odze RD and Goldblum, eds. Surgical pathology of the GI tract, liver,
biliary tract, and pancreas, Philadelphia: Saunders; 2009:355—394.
Greenson JK, Stern RA, Carpenter SL, et al: The clinical significance of
focal active colitis. Hum Pathol 1997; 28:729-733.
Volk EE, Shapiro BD, Easley KA, et al: The clinical significance of a biopsy-based
diagnosis of focal active colitis: A clinicopathologic study of 31 cases.
Mod Pathol 1998; 11:789-794