Sphincter of Oddi dysfunction: Year of the Zebra 2024

Sphincter of Oddi dysfunction, or SOD for short, is a group of rare conditions that occur when the sphincter of Oddi spasms, narrows, or relaxes inappropriately. The sphincter of Oddi is a muscular valve located between the biliary tree and small intestine. It’s responsible for regulating the flow of bile and pancreatic juices into the small intestine, and preventing reflux of intestinal content into the biliary tree.

With SOD, normal flow of bile and pancreatic juices is disrupted leading to biliary pain, which is pain typically located in the upper right abdominal quadrant.

There are three types of SOD. Type I consists of biliary pain, elevated liver enzymes, and a dilated common bile duct; type II includes biliary pain and either elevated liver enzymes or a dilated common bile duct; and type III includes biliary pain only.

The cause of SOD is unclear; though risk factors include being assigned female at birth; age 20 to 50 years; and a history of gallbladder removal.

The classic manifestation of SOD includes intermittent attacks of biliary pain, which is a type of colicky, abdominal pain that is typically located in the upper right quadrant, and can radiate to the back and shoulder. The pain can be mild to severe; lasts greater than 30 minutes; and can resolve spontaneously. These attacks feel and look similar to gallbladder attacks, though some individuals with SOD may not have a gallbladder. Other associated signs and symptoms may include nausea, vomiting, and pancreatitis, which is inflammation of the pancreas.

Diagnosis of SOD begins with a thorough history and physical examination. Typically, other more common causes of biliary pain are ruled out first, including gallstones. If SOD is suspected, blood tests and imaging may be done to aid in diagnosis. Blood tests may show elevated liver and pancreatic enzymes in those with types I or II. Imaging of the abdomen, including ultrasound, CT, or MRI may be done, as well as a HIDA scan, which can assess how the liver, gallbladder, and biliary tree are functioning.