Bile acid diarrhea

An overview of bile acid diarrhea, its causes, diagnosis, and treatment

Bile acid diarrhea (BAD), also known as bile acid malabsorption, is a condition characterized by chronic diarrhea due to excessive bile acids in the colon. This condition can significantly impact a patient's quality of life and is often underdiagnosed.

Pathophysiology

Bile acids are synthesized in the liver from cholesterol and are essential for the digestion and absorption of dietary fats. They are stored in the gallbladder and released into the small intestine after eating. Normally, over 95% of bile acids are reabsorbed in the ileum and returned to the liver via the enterohepatic circulation. In bile acid diarrhea, this reabsorption process is disrupted, leading to an excess of bile acids entering the colon, where they stimulate water and electrolyte secretion, resulting in diarrhea.

Causes

Bile acid diarrhea can be classified into three types based on its etiology:

• Type 1: Secondary to ileal disease or resection, such as in patients with Crohn's disease or those who have undergone ileal resection.
• Type 2: Idiopathic bile acid diarrhea, where no obvious cause is identified. This is sometimes referred to as primary bile acid diarrhea.
• Type 3: Associated with other gastrointestinal diseases, such as irritable bowel syndrome (IBS), celiac disease, or cholecystectomy.

Diagnosis

Diagnosing bile acid diarrhea can be challenging. The following tests are commonly used:

• SeHCAT test: A nuclear medicine test that measures the retention of a radiolabeled synthetic bile acid analogue. Low retention indicates bile acid malabsorption.
• Fecal bile acid measurement: Quantifies bile acids in stool, but is less commonly used due to technical difficulties.
• Serum C4 test: Measures 7α-hydroxy-4-cholesten-3-one, a marker of bile acid synthesis, which is elevated in bile acid diarrhea.

Treatment

The primary treatment for bile acid diarrhea involves the use of bile acid sequestrants, which bind bile acids in the intestine and prevent their laxative effect. Commonly used medications include:

• Cholestyramine
• Colestipol
• Colesevelam

These medications can be effective but may cause side effects such as bloating and constipation. Dietary modifications, such as a low-fat diet, may also help manage symptoms.

Prognosis

With appropriate treatment, many patients experience significant improvement in symptoms. However, ongoing management may be necessary, especially in cases related to chronic conditions like Crohn's disease.

Also see

• Crohn's disease
• Irritable bowel syndrome
• Cholecystectomy
• Celiac disease
• Enterohepatic circulation