Microscopic colitis

Microscopic colitis is an idiopathic inflammatory disease of the colon that manifests as chronic, nonbloody, watery diarrhea. There are three subtypes: lymphocytic colitis, collagenous colitis, and incomplete microscopic colitis. The condition is most common in women over 60 years of age and is associated with smoking, certain medications (e.g., NSAIDs and PPIs), and other autoimmune diseases. Diagnosis is based on the presence of chronic, watery diarrhea, a normal-appearing colon on colonoscopy, and characteristic histological findings in colon biopsy specimens. Treatment involves discontinuing offending agents and initiating pharmacological treatment (e.g., budesonide) to induce and maintain remission. Although the clinical course is variable, microscopic colitis is not associated with an increased risk of mortality.

• Microscopic colitis: : an idiopathic inflammatory disease of the colon characterized by chronic, nonbloody, watery diarrhea, normal macroscopic appearance of the bowel on colonoscopy, and collagenous or lymphocytic infiltrates on microscopy ^[1]
• Collagenous colitis: a histological subtype of microscopic colitis characterized by proliferation of collagenous connective tissue that forms a thick subepithelial collagen band ^[2]
• Lymphocytic colitis: a histological subtype of microscopic colitis characterized by intraepithelial lymphocytic infiltrates and little to no proliferation of connective tissue ^[2]
• Incomplete microscopic colitis: a histological subtype of microscopic colitis that has features of both collagenous and lymphocytic colitis but does not fulfill the histological criteria of either ^[2]

Outcomes and treatment recommendations do not differ between subtypes. ^[3]

• Peak incidence: 60–65 years ^[1]
• ♀ > ♂ ^[1][2]
• Present in ∼ 13% of patients with unexplained chronic, watery diarrhea ^[2]

Epidemiological data refers to the US, unless otherwise specified.

• Risk factors ^[4]
  • Older age
  • Female sex
  • Smoking ^[2][4]
• Associated medications ^[3][4]
  • PPIs
  • NSAIDs
  • Selective serotonin reuptake inhibitors
  • Statins
• Associated autoimmune diseases ^[2][4]
  • Celiac disease
  • Rheumatoid arthritis
  • Thyroid disorders (e.g., hypothyroidism or hyperthyroidism)
  • Type 1 diabetes mellitus

The pathogenesis is complex and not fully understood, but several mechanisms have been proposed. ^[1]

• Genetic predisposition ^[1]
• Changes to gut microbiome
• Autoimmunity
• Bile acid malabsorption ^[1]

• Chronic, nonbloody, watery diarrhea
• Weight loss
• Abdominal pain
• Fecal urgency
• Fecal incontinence
• Nocturnal stools

• Consider microscopic colitis in adults with chronic diarrhea. ^[3]
• Screen for diarrhea red flags that suggest an organic cause of diarrhea. ^[1]
• Refer to gastroenterology.
• Histopathological analysis of colon biopsy specimens is required to confirm the diagnosis. ^[4]
• Routine blood tests are not diagnostic but may be used to rule out differential diagnoses. ^[1]
• Assess for electrolyte abnormalities and dehydration in severe cases. ^[4]

The colon typically appears normal on colonoscopy. ^[3]

See “Etiology of chronic diarrhea.”

The differential diagnoses listed here are not exhaustive.

General principles ^[2][3][4]

• The primary goal of treatment is symptom relief and improved quality of life.
• Discontinue any offending agents (e.g., NSAIDs, PPIs) if possible.
• Antidiarrheals (e.g., loperamide, bismuth subsalicylate) can be used for persistent mild to moderate symptoms. ^[4]
• Budesonide is the preferred agent for inducing and maintaining remission in patients with moderate to severe symptoms. ^[3]
• Bile acid sequestrants (e.g., cholestyramine) can be used for patients with concomitant bile acid diarrhea.

Pharmacological treatment ^[3]

• Induction of remission
  • Indication: moderate to severe symptoms
  • Preferred agent: budesonide (off-label) for 6–8 weeks ^[2][3]
• Maintenance of remission
  • Indication: symptom recurrence after discontinuation of induction therapy
  • Preferred agent: low-dose budesonide for 6–12 months ^[2][3]
• Refractory disease: thiopurines OR anti-TNF agents OR vedolizumab ^[2]

• Variable disease course: Spontaneous remission, intermittent symptoms, or chronic and progressive disease can occur. ^[4]
• Microscopic colitis is not associated with an increased risk of mortality or colorectal malignancy or adenoma. ^[2][3]