Inside Tract - Sphincter sleuthing
Date: March 1, 2012
Any clinician who’s dealt with sphincter of Oddi dysfunction (SOD) knows The Dilemma.
It’s not the disorder itself—the fact that the sphincter, for reasons unknown, has become hypertensive and goes into spasms. The dilemma is that nearly two-thirds of patients respond quite well to the endoscopic therapy that relieves the disorder’s often-intense pain, but the other third, with identical symptoms, don’t always have the same success.
And unfortunately for that group, says gastroenterologist Mouen Khashab, there’s no good sign to tell who will benefit and who won’t.
Any patient faces small but real risks from endoscopic cutting of the sphincter of Oddi, and from the endoscopic probing that precedes it, with the main concern being pancreatitis. But for the unpredictable patients, “we believe that risk is overly high for the benefit,” Khashab says.
He’s working to resolve the dilemma.
Patients often come to Hopkins undiagnosed, typically after repeated attacks of right abdominal pain and nausea. Khashab and colleagues first rule out common GI disease—irritable bowel, for example, peptic ulcer or bile duct stones. They order more SOD-specific tests such as liver function and scans of the common bile duct—“labs” that would reflect a spastic sphincter hindering the normal flow of pancreatic fluid and bile into the small bowel.
It’s with this testing that the groups diverge.
Type I SOD has clear pathology, namely, abnormal liver or pancreatic function and a dilated bile and/or pancreatic duct. Patients with type II have only one of these.
The surprise is type III, where tests and scans come back normal—they’re unremarkable.
Fortunately, endoscopic manometry, the gold standard, nails SOD even in type III patients. Though feeding a pressure-sensing endoscope through the sphincter in itself carries a pancreatitis risk, manometry does pick up spasms.
As for therapy, patients with types I and II typically do well with sphincterotomy. With type III, that’s less sure; some 35 percent aren’t helped. “What’s clearly needed,” says Khashab, “is a way to predict who’ll benefit.”
So this summer, Khashab explores one possibility. He’s opening a clinical trial for an alternative diagnostic test for type III SOD patients. Half will undergo endoscopic manometry and half get a HIDA scan, a noninvasive measure of sphincter pressure. With HIDA, an injected radioactive tracer is tracked from liver to bile duct to small bowel. The technique, developed years ago at Hopkins, “is easier on patients,” Khashab says, “with no risk of pancreatitis.” It also brings the added benefit of a quantitative score.
Says Khashab: “We’re looking for certainty.”