What are the causes of microscopic colitis?

From the Guidelines

Microscopic colitis is a condition characterized by chronic watery diarrhea caused by inflammation in the colon's lining that is only visible under a microscope, with the exact cause remaining unclear but several factors contributing to its development, including autoimmune disorders, medications, bacterial or viral infections, genetic predisposition, and bile acid malabsorption, as reported in the most recent and highest quality study 1. The condition has two main subtypes: lymphocytic colitis and collagenous colitis.

• The inflammation disrupts normal water absorption in the colon, leading to persistent watery diarrhea.
• Other symptoms may include abdominal pain, fatigue, weight loss, and urgency to defecate.
• Diagnosis requires colonoscopy with biopsies since the colon appears normal during visual examination, and the inflammation is only detectable microscopically.
• The goal of medical therapy is to relieve symptoms and improve quality of life while minimizing drug-related adverse effects, as stated in the American Gastroenterological Association Institute guideline on the medical management of microscopic colitis 1.
• The condition is more common in older adults, particularly women over 50, with a reported prevalence ranging from 48 to 219 per 100,000, as noted in the guideline 1.
• Conditions associated with microscopic colitis include autoimmune diseases, such as rheumatic disease, thyroid disease, and coeliac disease, as well as bile acid diarrhoea, as reported in a systematic review and meta-analysis 1.
• The persistence of residual bowel symptoms may also reflect coexisting or postinflammatory functional bowel disorders, and patients with refractory symptoms should avoid potential medication triggers, such as nonsteroidal anti-inflammatory drugs, proton pump inhibitors, and selective serotonin reuptake inhibitors, as recommended in the guideline 1.

From the Research

Microscopic Colitis Causes

The causes of microscopic colitis are not fully understood, but several risk factors have been identified, including:

• Increasing age 2, 3, 4, 5, 6
• Female sex 2, 3, 4, 5, 6
• Presence of other autoimmune diseases 2, 3, 4, 5, 6
• Use of certain medications, such as:
  • Proton pump inhibitors 2, 3, 6
  • Nonsteroidal anti-inflammatory drugs 2, 3, 6
  • Selective serotonin reuptake inhibitors 2, 3
  • Statins 2
• Smoking 3, 4, 6
• Alcohol use 6
• Immune-mediated diseases 6
• Select gastrointestinal infections 6

Pathophysiology

The pathophysiology of microscopic colitis is thought to be related to an aberrant immune response to the luminal microenvironment in genetically susceptible individuals 4, 5, 6. An inappropriate immune response to disturbances in the gut microenvironment is implicated in the pathogenesis of microscopic colitis 5. Evidence also supports an underlying genetic basis for disease 5.

Etiology

The etiology of microscopic colitis is unknown, but it is associated with autoimmune disorders, such as celiac disease, polyarthritis, and thyroid disorders 3. Exposure to medications is suspected to play a role in microscopic colitis, although their direct causal relationship has not been proven 3.