What is the recommended management approach for descending colitis?

Management of Descending Colitis

For descending colitis, initiate combination therapy with oral mesalamine 2-4g daily plus topical mesalamine enemas 1g daily, as this provides superior efficacy compared to either agent alone. 1, 2

First-Line Treatment Approach

Combination oral and topical therapy is the cornerstone of management:

• Start oral mesalamine 2-4g daily (or balsalazide 6.75g daily, or olsalazine 1.5-3g daily) combined with topical mesalamine enemas 1g daily 1, 2
• Use liquid enemas rather than suppositories or foam for descending colon involvement, as enema preparations are needed to reach inflammation extending beyond the sigmoid colon 1
• Once-daily dosing of oral mesalamine is as effective as divided doses and improves adherence 2, 3
• Topical mesalamine enemas are more effective than oral mesalamine alone for left-sided disease 1

Important caveat: While the 2019 AGA guidelines note that enema preparations are unlikely to reach proximal to the sigmoid colon, patients with descending colon involvement should still receive combined oral and topical therapy for optimal outcomes 1. The oral component addresses the more proximal inflammation while topical therapy maximizes local anti-inflammatory effect in the distal segments 2.

Second-Line Treatment for Inadequate Response

If no improvement after 2-4 weeks of optimized combination therapy:

• Initiate oral prednisolone 40mg daily 1, 2
• Continue topical mesalamine as adjunctive therapy alongside systemic corticosteroids 1, 2
• Taper prednisolone gradually over 8 weeks according to clinical response; more rapid reduction increases relapse risk 1, 2
• Topical corticosteroids are less effective than topical mesalamine and should only be used as second-line for patients intolerant of topical mesalamine 1, 2

Steroid-Dependent or Refractory Disease

For patients requiring prolonged corticosteroids or failing to respond adequately:

• Initiate azathioprine 1.5-2.5 mg/kg/day or mercaptopurine 0.75-1.5 mg/kg/day as steroid-sparing agents 2, 4
• Avoid long-term corticosteroid use due to significant adverse effects 2
• Consider cyclosporine for severe, steroid-refractory colitis in specialized centers 2, 4

Severe Disease Requiring Hospitalization

Admit patients who meet Truelove and Witts' criteria or fail maximal oral therapy:

• Initiate intravenous corticosteroids with joint medical-surgical management 1
• Monitor vital signs four times daily, daily stool charts, and laboratory parameters (CBC, CRP, electrolytes, albumin) every 24-48 hours 1
• Obtain daily abdominal radiographs if colonic dilatation (transverse colon >5.5cm) is present 1
• Provide IV fluid/electrolyte replacement, blood transfusion to maintain hemoglobin >10 g/dL, and subcutaneous heparin for thromboprophylaxis 1
• Maintain close liaison with colorectal surgery; patients should understand there is a 25-30% chance of requiring colectomy 4

Maintenance Therapy

Once remission is achieved:

• Lifelong maintenance therapy with aminosalicylates is recommended for all patients with descending colitis 1, 2, 5
• Mesalamine ≥1.2g daily provides colorectal cancer chemoprevention benefit 6
• For steroid-dependent patients, continue azathioprine or mercaptopurine long-term 2

Critical Pitfalls to Avoid

• Do not use antidiarrheal medications as they mask worsening symptoms while allowing inflammation to progress 2
• Do not delay corticosteroid initiation if no response to optimized 5-ASA therapy after 2-4 weeks 2
• Ensure adequate mesalamine dosing of at least 2g daily for active disease; lower doses are insufficient 2
• Confirm disease activity by sigmoidoscopy and exclude infection before escalating treatment, though do not delay corticosteroids while awaiting stool cultures 2, 4
• Treat proximal constipation with stool bulking agents or laxatives, as this can worsen distal inflammation 1, 2