What is Sphincter of Oddi dysfunction?

Sphincter of Oddi Dysfunction (SOD)

Sphincter of Oddi dysfunction is a functional disorder characterized by abnormal contractility of the sphincter of Oddi, causing obstruction to the flow of bile and pancreatic secretions, resulting in biliary-type pain, elevated liver enzymes, and potential pancreatitis. 1

Anatomy and Physiology

The sphincter of Oddi is a smooth muscle valve located at the junction of the bile duct and pancreatic duct with the duodenum. It serves critical functions:

• Regulates the flow of bile and pancreatic juice into the duodenum
• Prevents reflux of duodenal contents into the biliary and pancreatic ducts
• Maintains pressure in the common bile duct higher than that in the duodenum or gallbladder 1

The normal sphincter function involves:

• Prominent phasic contractions superimposed on basal pressure during fasting
• Relaxation in response to cholecystokinin (CCK) released after meals, allowing bile and pancreatic juice to flow into the duodenum 2

Classification

SOD is classified according to the Milwaukee classification system:

1. Type I SOD:

   • Biliary pain
   • Elevated liver enzymes (>2 times normal)
   • Dilated common bile duct (>12 mm)
   • Delayed drainage of contrast (>45 minutes) 3, 4

2. Type II SOD:

   • Biliary pain
   • Only one of the above objective findings 3, 4

3. Type III SOD:

   • Biliary pain only
   • No objective findings 3, 4

Pathophysiology

SOD can manifest through two primary mechanisms:

1. Anatomical stenosis: Structural narrowing of the sphincter
2. Sphincter dysmotility: Functional disorder with abnormal contractions 3

Proposed mechanisms include:

• Gallbladder hypomotility
• Partial structural or functional outlet obstruction
• Discoordination between gallbladder contraction and sphincter of Oddi relaxation
• Visceral hypersensitivity 1

Risk Factors

Several factors increase the risk of developing SOD:

• Cholecystectomy: Post-cholecystectomy patients have higher rates of SOD
• Opioid use: Causes sphincter spasm and dysfunction
• Alcohol consumption: May affect sphincter motility
• Female gender: SOD is more common in women 5

Clinical Presentation

Patients with SOD typically present with:

• Recurrent episodes of right upper quadrant or epigastric pain
• Pain that may radiate to the back or shoulder
• Episodes lasting 30 minutes to several hours
• Elevated liver enzymes during pain episodes (in Type I and some Type II)
• History of recurrent pancreatitis in some cases 6

Diagnosis

The diagnostic approach to SOD includes:

1. Sphincter of Oddi manometry: Currently the gold standard for diagnosis

   • Measures sphincter pressure (>40 mmHg is abnormal)
   • Carries significant risk of post-procedure pancreatitis (>30%) 6

2. Non-invasive tests:

   • Hepatobiliary scintigraphy: Evaluates bile flow
   • Magnetic resonance cholangiopancreatography (MRCP): Assesses duct anatomy
   • Endoscopic ultrasound: Rules out other biliary pathology
   • Fatty meal ultrasonography: Evaluates duct dilation after stimulation 4

3. Therapeutic trials:

   • Botulinum toxin injection: May predict response to sphincterotomy
   • Trial stenting: Temporary stent placement to assess symptom improvement 3

Management

Treatment approaches vary by SOD type:

Type I SOD

• Endoscopic sphincterotomy is recommended without prior manometry
• Success rates range from 55-95% 3, 6

Type II SOD

• Sphincter of Oddi manometry should guide therapy
• Endoscopic sphincterotomy for patients with abnormal manometry
• Consider trial of medical therapy before invasive procedures 3

Type III SOD

• Medical therapy is first-line treatment
• Poor outcomes from sphincterotomy
• High complication rates from manometry
• Alternative diagnoses should be thoroughly explored 3

Medical Therapy Options

• Smooth muscle relaxants: Nifedipine, nitrates
• Anticholinergics: Hyoscyamine
• Tricyclic antidepressants: For pain modulation
• Avoidance of opioids: Can worsen sphincter dysfunction 5, 2

Complications

SOD is associated with significant complications:

• Acute pancreatitis: SOD is a risk factor for recurrent acute pancreatitis
• Post-ERCP pancreatitis: Rates exceed 30% in SOD patients
• Chronic pancreatitis: May develop in untreated cases 6

Prognosis

Outcomes vary based on SOD type and treatment approach:

• Type I SOD has the best response to sphincterotomy
• Type II SOD has variable response, better when guided by manometry
• Type III SOD has poor outcomes with sphincterotomy and high procedural risks 3

For patients with pancreatic SOD, up to 88% may benefit from sphincterotomy of the pancreatic sphincter 6.