Sphincter of Oddi function and dysfunction: Investigation of SO dysfunction
Blood screens during an acute attack of pain reveal a normal white cell count. About 10% to 20% of patients, however, show increases in serum concentrations of liver transaminases, particularly in blood specimens that are taken 3 to 4 h after the onset of pain. This is occasionally accompanied by increases in serum bilirubin and AP. In a subgroup of patients, serum amylase may be elevated either alone or in conjunction with changes in liver enzymes, and these patients are then considered to have the pancreatic form of the disorder.
Typical pain episodes of SO dysfunction are quite characteristic, but often other functional bowel disturbances can coexist, making diagnosis on history alone difficult. A trial of therapy for suspected irritable bowel syndrome can be considered where the history is vague, in the hope that this may improve symptoms and exclude SO dysfunction as a diagnostic possibility. Common bile duct stones need to be excluded in all patients with suspected SO dysfunction. The role of magnetic resonance cholangiopancreatography (MRCP) in evaluating the biliary tree in patients with a low likelihood of having common bile duct stones is unclear. At present, MRCP has not been shown to be superior than an ultrasound in detecting common bile duct stones. ERCP has the obvious advantage of being able to remove common bile duct stones at the time of the procedure and can also give an indication as to the possibility of SO dysfunction being present by an objective measurement of common bile duct diameter and whether contrast drains adequately. While these factors have not been shown to predict SO dysfunctions reliably, they can help in deciding whether to proceed to other investigations once common bile duct stones have been excluded. Pain on injection of contrast during ERCP has not been found to correlate with SO dysfunction. Biopsies from the papilla in a large series of patients with SO dysfunction found a 4.3% incidence of adenoma. If there is any suspicion that the papilla appears abnormal, biopsies should be considered.
The morphine-neostigmine test or Nardi test has been used in the past as a way to try and predict the response to sphincter division, either surgically or endoscopically. It is a very sensitive test, but lacks specificity and has little role in the investigation of patients with suspected SO dysfunction.
Symptomatic improvement with common bile duct stenting has been shown to predict response to sphincterotomy. However, one study showed a high rate of pancreatitis, and more studies are required before this approach can be recommended.
Biliary scintigraphy, which uses an imino acid that is taken up by hepatocytes and secreted unchanged into the biliary system while coupled to radioactive technitium, allows an assessment of bile flow. By being able to scan a region of interest over the biliary tree, time activity curves for bile flow can be generated. CCK is often administered to stimulate bile flow. Obstruction of the biliary tree has been shown to reduce bile flow, as assessed by scintigraphy. Many variables are used to assess obstruction, including the time taken to the maximal count over the biliary tree (T max); the time taken for 50% of tracer to be seen over the biliary tree (half-life); the time taken for the tracer to enter the duodenum; prolonged excretion of tracer from the biliary tree; and the transit time of tracer from the hepatic hilum to the duodenum.
Although initial experience was generally favourable, there was variability in the parameters used for scintigraphy and diagnostic criteria for SO dysfunction. Sphinc- terotomy has been shown to improve bile flow, often to normal values. One study assessed many scin- tigraphic variables and found that the hepatic hilum to duodenal transit time is the best predictor of delayed bile flow into the duodenum. This variable was then studied prospec- tively against SO manometry in patients with suspected SO dysfunction and found to have an 83% sensitivity and a 100% specificity. However, in patients with a dilated common bile duct, sphincterotomy was not found to normalize bile flow. A scoring system using six scintigraphic variables has been developed in an attempt to improve the accuracy of scintigraphy in patients with suspected SO dysfunction. In the 26 patients studied, 100% sensitivity and specificity of scintigraphy were found when compared with manometric criteria. These studies have not been repeated; thus, the results need to be confirmed before scintigraphy replaces manometry. A likely role for scintigraphy will be as a screening test, with manometry being used for equivocal results. Scintigraphy has not been found to be useful in diagnosing patients with suspected SO dysfunction and an intact gallbladder.
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