Sphincter of Oddi Dysfunction: Tiny Valve, Huge Problems
Sphincter of what? Many of us may not even know there is such a thing as a Sphincter of Oddi, one of the lesser-known muscles within our bodies that play a crucial part in our digestive system. It is the smooth circular muscle found at the same level as the common channel (also called ampulla of Vater) where the common bile duct and the main pancreatic duct meet. Small as it is, this sphincter controls the flow of bile and pancreatic juice into the duodenum as well as the diversion of hepatic bile into the gallbladder. Since it is a one way valve, it also prevents the backflow of the contents (including food and digestive juices) from the duodenum of the small intestine. When we eat, numerous factors control the contraction and relaxation of this muscle. Through brain signals, peptides and hormones open and shut the valve, letting out the necessary amount of digestive fluid proportional to our intake.
However, that complex mechanism may sometimes fail due to several reasons. The first and most common is the occurrence is that of post-cholecystectomy syndrome. PCS is accompanied by a set of symptoms after gallbladder removal ranging from abdominal discomfort including gas, indigestion, heartburn, etc. to excruciating pain. Some symptoms happen to up to 60% of removal patients. The symptoms of SOD which are at least moderate to severe ones and are reported to occur in 15%, but it is possible that many go undiagnosed.
Another possible cause for the dysfunction of the SO is the growth of tumors that involve other parts of the biliary system (such as the ampulla of Vater or the papillary orifice). Third possible cause is recurrent pancreatitis.
- Post-cholecystectomy syndrome
- Tumors within the biliary system
- Recurrent idiopathic pancreatitis
So what exactly is Sphincter of Oddi Dysfunction?
Sphincter of Oddi Dysfunction (SOD) refers to the structural or functional disorder that impedes the normal flow of bile and pancreatic juice. The two major forms of dysfunction are papillary stenosis and sphincter of Oddi dyskinesia.
- Narrowing - Papillary stenosis – It is brought about by an abnormality wherein the sphincter of Oddi becomes partially or completely narrowed. Conditions that are thought to result in stenosis include pancreatitis, injury from gallbladder or bariatric surgery, inflammatory conditions, and the presence of stones inside the common bile duct.
- Malfunction - Sphincter of Oddi Dyskinesia – This refers to a dysfunction in the sphincter that may cause unexplained biliary pain.
Because of the overlap of symptoms and the difficulty to pinpoint the specific cause of the disorder, the term Sphincter of Oddi Dysfunction was developed to capture both types.
Sphincter of Oddi Dysfunction Symptoms
- Recurring severe or moderate pain that lasts for more than 20 minutes
- Lasting for more than 20 minutes
- Continuing for more than 3 months
- Located in upper right abdomen below the rib cage
- May radiate into the back shoulder blade
- Accompanied by nausea and/or vomiting
- May occur after a meal
- Often occurs at night
- Pain may also occur on the left side of the rib cage (and improve on bending forward)
- May include changing stools – constipation or diarrhea
- Indigestion, gas, bloating, heatburn, burping
What is the relationship between SOD and gallbladder removal?
Doctors often suspect SOD in patients who experience repetitive pain attacks after gallbladder removal or cholecystectomy. Statistics tell us that of the 750,000 gallbladder surgeries performed in the US every year and 40-60% experience symptoms after removal. Among these, between 14-23% are diagnosed with SOD.
The prevalence of SOD among cholecystectomy patients may mean two things - either the SOD was affected by the loss of the gallbladder or that SOD has been the cause of the symptoms all along. Pain caused by SOD in gallbladder patients may be felt several years after a cholecystectomy. Alternatively, they may have continued pain not relieved by the surgery, which reminds us that gallbladder removal is not a fool proof way to rid ourselves of pain.
How is Sphicter of Oddi Dysfunction Diagnosed?
The diagnostic testing systems for SOD are not perfect. Numerous laboratory, non-invasive, and invasive procedures can be conducted to determine if a person indeed has SOD. But before that, doctors would often try to find out if there are other underlying conditions for the abdominal pain. Since SOD symptoms are general, they can mimic other diseases like peptic ulcer, stones, pancreatitis, or others. For patients who have had prior cholecystectomy, clinical suspicion of SOD is more common.
Initial laboratory procedures include biochemical test of liver function and blood test to determine dilation of the bile duct. SOD patients would show elevated levels of serum aminotransferases.
Suspicions rising from symptoms and lab results can be confirmed by performing other non-invasive tests such as the following:
- Morphine-Prostigmin Provocative Test (Nardi Test)
- Hepatobiliary Scintigraphy
- Magnetic resonance Cholangiopancreatography (MRCP)
There are also more invasive procedures that are said to be more accurate in identifying the presence of SOD. In general, these are not recommended unless definitive therapy is planned for abnormal sphincter function.
- Endoscopic Retrograde Cholangiopancreatography (ERCP)
- Sphincter of Oddi Manometry (SOM)
The combination of ERCP and SOM, as complicated as they are, still remain to be the gold standard in ascertaining sphincter of Oddi dysfunction.
What are the categories of sphincter of Oddi dysfunction?
After conducting clinical and laboratory tests to determine whether a person is suffering from SOD, doctors categorize their patients using the Milwaukee Biliary Group Classification of SOD. This helps them identify the course of treatment and the outcome from endoscopic sphincterotomy or surgical sphincteroplasty.
- Type I Patients have a known structural disorder of the sphincter. They present biliary-type pain, their aspartate transaminase (AST) and alanine transaminase (ALT) levels are more than twice the normal values, their common bile ducts are dilated, and they have delayed drainage of bile duct and pancreatic juices.
- Type II Patients also have biliary-type pain but they only demonstrate sphincter of Oddi motor dysfunction in 50-65% of the cases.
- Type III Patients have severe abdominal pain but with little or no abnormalities on blood tests and scans (including MCRP).
For both Type II and III patients, endoscopic manometry is important to diagnose sphincter of Oddi dysfunction. Type I patients almost certainly have papillary stenosis and may be treated without the need for further investigation.
Patients with a similar pain problem, but who have little or no abnormalities on blood tests and standard scans (including MRCP), are categorized as having SOD Type III. The episodes of pain are assumed due to intermittent spasm of the sphincter. It is very difficult to effectively evaluate and manage patients with Type III SOD. Some physicians are skeptical of its existence, or assume that it is a part of a broader problem of a functional digestive disturbance such as irritable bowel syndrome. Other physicians assert that without the gallbladder, the balance of the bile has changed, causing an inflammation in the bile ducts and sphincter of Oddi and address both the inflammation and the bile.
What’s the treatment for sphincter of Oddi dysfuction?
There are different modes of treatment for sphincter of Oddi depending on the severity. Historically, great emphasis is given to definite intervention like surgery. Although this is extremyly necessary in some case, some other forms of therapy may still do the job for other types of SOD.
- Medical Therapy
Since the sphincter of Oddi is a smooth muscle, some drugs that can relax muscles are believed to be effective in restoring normal SO function. Sublingual nifedipine and nitrates have been proven to reduce the pressure and resistance of the SO to ductal pressure. The use of antispasmodid drugs and antidepressants are also known to reduce the pain and discomfort. Despite the convenience of this treatment, medication side-effects need to be considered. Also, if SOD is caused by structural defects, muscle relaxants will definitely be ineffective. Generally, this route is recommended to Type II and III patients before considering more aggressive steps.
- Surgical Therapy
Surgery in the form of transduodenal biliary sphincteroplasty with a transampullary septoplasty is the traditional way SOD is treated. In a study following-up patients who have undergone the procedure, it was found that 60-70% benefited from having the surgery. However, with the dawn of endoscopy, surgery has taken the back seat. Endoscopic therapy is now more favoured because of its degree of invasiveness, cost of care, morbidity, mortality, and cosmetic results.
- Endoscopic Sphincterotomy
This technology is now the prevailing gold standard in treating patients with SOD. It is important to note, however, that patients undergoing endoscopic sphincterotomy for SOD have complication rates 2-5 times higher than patients undergoing endoscopic sphincterotomy for ductal stones, According to studies, pancreatitis is the most common complication occurring in up to 20% of patients. At the moment, there are a lot of efforts given to develop better techniques to limit such complications.
- Botulinium toxin (Botox) Injection
One of the more recent procedures for SOD treatment is the injection of Botox into the muscle. This has been successful in addressing smooth muscle disorders of the gastrointestinal tract such as achalasia. It has also resulted in the significant reduction of pressure in the basal sphincter, allowing the relaxation of the SO resulting to improved bile flow.
- Anti-Inflammatories and Bile Salts
A more unconventional, yet less invasive approach is to use cox-2 inhibitors (medications or natural ones) to reduce the inflammation throughout the ducts and sphincters and to address the increased toxicity or hydrophobic state of the bile with ursodeoxycholic acid.
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