How Should Microscopic Colitis Be Diagnosed and Treated?

Answer in brief: Microscopic colitis should be suspected in chronic non-bloody watery diarrhea, particularly in middle-aged or older adults, even when colonoscopy appears normal. Diagnosis requires colonic biopsies because the mucosa often looks normal endoscopically. Budesonide is the best-supported first-line therapy for induction, and recurrent disease often responds to maintenance budesonide. Medication triggers and coexisting celiac or thyroid disease should be considered.

Key clinical points

Normal colonoscopic appearance does not exclude microscopic colitis.
Obtain biopsies from more than one colonic segment.
Budesonide is preferred over mesalamine for induction.
Review medications associated with microscopic colitis, including NSAIDs, PPIs and some SSRIs, without assuming causation in every case.

Clinical phenotype

The classic presentation is persistent watery diarrhea without visible blood, often with urgency, nocturnal stooling and fecal incontinence. Weight loss and abdominal discomfort can occur. The differential includes infection, bile-acid diarrhea, celiac disease, medication effects, IBS-D and endocrine disease.

Diagnosis

Colonoscopy is performed largely to exclude other pathology and obtain biopsies. Because histologic abnormalities can be patchy, samples should be obtained from both right and left colon. Lymphocytic colitis and collagenous colitis share similar clinical management but have different histologic definitions.

Treatment

AGA guidance recommends budesonide for induction and favors it over mesalamine. Patients who relapse after stopping induction frequently respond to maintenance budesonide at the lowest effective dose. When budesonide is not feasible, alternatives such as bismuth or mesalamine may be considered, although the evidence is weaker. Severe refractory cases require confirmation of diagnosis and exclusion of bile-acid diarrhea, celiac disease and ongoing medication triggers.

Medication review

Associations exist with several common drugs, but stopping a medication should be individualized according to indication and temporal relationship. Avoiding unnecessary NSAIDs and smoking cessation are reasonable general measures.

Practical approach

1. Confirm chronic watery non-bloody diarrhea and review medications.

2. Perform colonoscopy with right- and left-colon biopsies even if mucosa appears normal.

3. Use budesonide for symptomatic induction when appropriate.

4. For recurrence, reassess triggers and consider maintenance budesonide at the lowest effective dose.

Common errors to avoid

Failing to biopsy normal-appearing colon in chronic watery diarrhea.
Using mesalamine as equivalent first-line therapy to budesonide despite weaker evidence.

Trainee takeaway

Microscopic colitis should be suspected in chronic non-bloody watery diarrhea, particularly in middle-aged or older adults, even when colonoscopy appears normal. The examination question is usually less about memorizing one cutoff than recognizing which finding changes the next clinical decision.

Relevant free books by Dr. Alan B. R. Thomson

Thomson ABR. Practice Review in Gastroenterology. CAPstone Academic Publishers; 2014. ISBN 978-1500855321.
Thomson ABR. Guideline-Based Management in Gastroenterology. CAPstone Academic Publishers; 2015. ISBN 978-1515078623.

Free downloads: https://giandhepatology.com/free-medical-books-on-gastroenterology-and-hepatology

Frequently asked questions

Can microscopic colitis be seen during colonoscopy?

Usually not. The colon often looks normal, which is why biopsies are essential.

Is budesonide systemic steroid therapy?

Budesonide has high first-pass hepatic metabolism and lower systemic exposure than prednisone, although prolonged use can still have steroid-related effects.

References

1. Thomson ABR. Practice Review in Gastroenterology. CAPstone Academic Publishers; 2014. ISBN 978-1500855321.

2. Thomson ABR. Guideline-Based Management in Gastroenterology. CAPstone Academic Publishers; 2015. ISBN 978-1515078623.

3. Nguyen GC, Smalley WE, Vege SS, Carrasco-Labra A. American Gastroenterological Association Institute Guideline on the Medical Management of Microscopic Colitis. Gastroenterology. 2016;150:242-246.

Editorial note: This educational article synthesizes Dr. Thomson’s teaching framework with current society guidance. Recommendations should be checked against the latest guideline, local formulary, regulatory labeling and the individual clinical context before patient-specific use.