What is the treatment approach for a newly diagnosed patient with microscopic colitis presenting with regular loose bowel movements, and how can it be differentiated from Irritable Bowel Syndrome with Diarrhea (IBS-D)?

Treatment of Microscopic Colitis

For a newly diagnosed patient with microscopic colitis presenting with regular loose bowel movements, budesonide 9 mg daily is the first-line treatment for induction of clinical remission, with strong evidence supporting its superiority over all other options. 1, 2

Differentiating Microscopic Colitis from IBS-D

Microscopic colitis and IBS-D present with remarkably similar symptoms, making clinical differentiation challenging:

• Both conditions share: chronic watery non-bloody diarrhea, abdominal pain, bloating, and flatulence 1, 3
• Key distinguishing features of microscopic colitis: nocturnal diarrhea and fecal incontinence are frequently present, which are less common in IBS-D 4, 5
• Definitive diagnosis requires: colonoscopy with biopsies from normal-appearing mucosa, as the colon appears endoscopically normal in microscopic colitis 6, 5
• Biopsy protocol: minimum of 2 samples from right colon (ascending/transverse) and left colon (descending/sigmoid), plus rectum, placed in separate containers 6
• Critical point: biopsies only from rectum miss 34-43% of cases; ascending colon has highest diagnostic yield at 96.9% 6

Studies show that 6% of patients initially diagnosed with IBS-D actually have microscopic colitis when properly evaluated 3. The American Gastroenterological Association recommends colonoscopy with biopsies for diarrhea-predominant symptoms, particularly for loose/watery stools 1.

First-Line Treatment Approach

Budesonide (Entocort) 9 mg daily is the strongly recommended first-line therapy:

• Efficacy: Induces clinical remission with moderate-quality evidence, ranking first among all treatment options 1, 2, 7
• Superiority: Budesonide is superior to mesalamine with high-quality evidence 1, 2
• Response rate: Approximately 44-47% of patients respond to initial treatment 4, 8
• Histological improvement: Also ranks first for histological remission (RR: 13.39) 7

Before starting budesonide, identify and discontinue triggering medications:

• High-risk medications: NSAIDs, proton pump inhibitors, SSRIs, statins, ranitidine, and sertraline 2, 5, 9
• Evidence: Limited but recommended by the American Gastroenterological Association 2

Adjunctive symptomatic therapy:

• Loperamide can be used for immediate symptomatic relief alongside budesonide 5, 9
• Bile acid sequestrants: Consider if bile acid diarrhea is suspected (present in 41% of collagenous colitis, 29% of lymphocytic colitis) 1, 4

Alternative First-Line Options (When Budesonide Not Feasible)

If budesonide cannot be used due to contraindications or cost:

1. Mesalamine: Conditional recommendation with moderate-quality evidence 1, 2
2. Bismuth salicylate: 8-9 tablets daily divided three times daily; conditional recommendation with low-quality evidence, but significant pill burden 1
3. Prednisolone/Prednisone: Conditional recommendation with very low-quality evidence; reserve for refractory cases due to systemic side effects 1, 2

Not recommended treatments:

• Combination cholestyramine + mesalamine: No benefit over mesalamine alone 1
• Boswellia serrata: Conditional recommendation against use 1
• Probiotics: Conditional recommendation against use 1

Maintenance Therapy

For patients who relapse after stopping induction therapy:

• Budesonide maintenance is strongly recommended with moderate-quality evidence 1, 2
• Dosing: Start with 6 mg daily, can taper to lowest effective dose 2
• Efficacy: Reduces clinical relapse risk by 66% (RR: 0.34,95% CI: 0.19-0.6) over 6 months 1, 2
• Optimal formulation: Budenofalk 6 mg/3 mg alternate-day dosing ranked first for maintenance (RR: 3.68) 7
• Duration: Consider 6-12 months before attempting discontinuation 2

Important consideration: Approximately one-third of patients may not require maintenance therapy after initial treatment, suggesting spontaneous remission can occur 4. Therefore, maintenance should only be offered to those who actually relapse 2, 4.

Monitoring and Long-Term Management

Bone health monitoring:

• Monitor for bone loss with prolonged budesonide use 2
• Consider osteoporosis prevention and screening in patients requiring long-term therapy 2

For refractory disease:

• Re-evaluate for other causes: celiac disease, functional bowel disorders, or post-inflammatory symptoms 2
• Severe refractory cases: Anti-TNF-alpha drugs (infliximab, adalimumab) are recommended as alternative to colectomy in cases failing corticosteroids or immunomodulators 10

Common Pitfalls to Avoid

• Do not rely on sigmoidoscopy alone: Must obtain biopsies from right colon, as disease can be focal 6
• Do not assume normal-appearing mucosa excludes diagnosis: Microscopic colitis requires histological confirmation 6, 5
• Do not use mesalamine as first-line in collagenous colitis: Budesonide is superior 10
• Do not continue high-risk medications unnecessarily: NSAIDs and PPIs should be discontinued when clinically possible 2, 5