What is Sphincter of Oddi dysfunction?

Sphincter of Oddi Dysfunction (SOD)

Sphincter of Oddi dysfunction is a clinical disorder characterized by abnormal contraction or relaxation of the sphincter of Oddi, which can lead to biliary pain, pancreatic pain, or both, due to obstruction of bile and pancreatic fluid flow into the duodenum. 1

Anatomy and Physiology

The sphincter of Oddi is a smooth muscle valve that:

• Controls the flow of bile and pancreatic secretions into the duodenum
• Maintains pressure in the common bile duct higher than in the duodenum or gallbladder during fasting
• Relaxes postprandially in coordination with gallbladder contraction 2

Normal function involves:

• Storage and concentration of bile in the gallbladder during fasting
• Coordinated contraction of the gallbladder with simultaneous relaxation of the sphincter after meals
• Regulation by hormonal and neural mechanisms, with cholecystokinin (CCK) being the principal hormone controlling this process 2

Pathophysiology

SOD occurs through several proposed mechanisms:

• Anatomical stenosis of the sphincter
• Functional sphincter dysmotility
• Discoordination between gallbladder contraction and sphincter relaxation
• Visceral hypersensitivity 2, 3

Biliary pain in SOD results from:

• Increased gallbladder pressure
• Abnormal contraction patterns
• Structural or functional outflow obstruction 2

Classification

SOD is typically classified into three types based on clinical presentation, laboratory findings, and imaging:

1. Type I (Definite):

   • Biliary-type pain
   • Abnormal liver enzymes (>2 times normal)
   • Dilated bile duct
   • Delayed drainage on imaging

2. Type II (Probable):

   • Biliary-type pain
   • Either abnormal liver enzymes OR dilated bile duct/delayed drainage

3. Type III (Possible):

   • Biliary-type pain only
   • Normal liver enzymes and imaging 1, 4

Diagnosis

Gold standard: Sphincter of Oddi manometry (SOM) - measures pressure within the sphincter 1, 4

Non-invasive alternatives:

• Magnetic Resonance Cholangiopancreatography (MRCP)
• Endoscopic Ultrasound (EUS)
• Hepatobiliary Scintigraphy (CCK-CS)
• Cholecystokinin-cholescintigraphy (CCK-CS) 2, 1

For CCK-CS testing:

• Standardized protocol using 60-minute CCK infusion is recommended
• Patient selection is critical - should meet Rome III criteria for functional biliary pain
• Should be performed when patients are not in pain or hospitalized 2

Risk Factors

Several factors may increase the risk of SOD:

• Cholecystectomy (post-cholecystectomy syndrome)
• Opioid medication use
• Alcohol consumption
• Liver transplantation (occurs in ~5% of recipients due to denervation) 1, 3, 5

Management

Treatment approach should be based on SOD type:

1. Type I SOD:

   • Endoscopic sphincterotomy is recommended without prior manometry
   • Favorable outcomes regardless of manometry results 1, 4

2. Type II SOD:

   • First-line: Trial of medical therapy with smooth muscle relaxants and pain management
   • If medical therapy fails, sphincter of Oddi manometry may predict response to endoscopic sphincterotomy
   • Alternative: Trial of Botox injection or temporary stenting 1, 4

3. Type III SOD:

   • Primarily medical management
   • High complication rates from manometry and poor outcomes from sphincterotomy
   • Alternative diagnoses should be thoroughly explored 1, 4

Medical therapy options:

• Smooth muscle relaxants (calcium channel blockers, nitrates)
• Pain management
• Tricyclic antidepressants 1, 3

Procedural considerations:

• Perioperative antibiotics when risk of cholangitis exists
• PEP prophylaxis with rectal NSAIDs to reduce post-ERCP pancreatitis risk
• Consider pancreatic stent placement if repeated pancreatic duct cannulation occurs 1

Important Clinical Considerations

• Eluxadoline is contraindicated in patients with sphincter of Oddi problems 1
• SOD is associated with intestinal dysmotility and visceral hyperalgesia 6
• Patient counseling about risks and benefits is essential, especially for Type II and III SOD 1
• Post-cholecystectomy patients are at higher risk for developing SOD 5
• Careful patient selection is critical for invasive procedures due to associated morbidity 4

Treatment Outcomes

• Type I SOD: Generally good response to sphincterotomy
• Type II SOD: Variable response to sphincterotomy, better if manometry is abnormal
• Type III SOD: Poor response to sphincterotomy, high complication rates 4

The diagnosis and management of SOD remains challenging, requiring a careful balance between invasive diagnostic procedures and their associated risks versus potential therapeutic benefits.