Toxic Megacolon

Risk factors

• Inflammatory bowel disease (UC > Crohn colitis)
• C. difficile colitis, especially in immunocompromised or recent antibiotics
• Other infectious colitides: Salmonella, Shigella, Campylobacter, E. histolytica, CMV (in immunosuppression)
• Ischemic colitis
• Medications that slow motility: opioids, anticholinergics, antidiarrheals (loperamide), antidepressants
• Recent colonoscopy or barium enema during active colitis
• Electrolyte derangements (hypokalemia, hypomagnesemia)

Pathophysiology

Severe transmural inflammation extends into the muscularis propria, paralyzing the smooth muscle and producing colonic dilation. Inflammatory mediators (nitric oxide, cytokines) further inhibit smooth muscle tone. Bacterial overgrowth and translocation produce systemic toxicity. Continued dilation thins the wall and risks perforation, especially in the transverse colon.

Clinical presentation

Differential diagnosis

• Ogilvie syndrome (acute colonic pseudo-obstruction) — Massive cecal dilation in critically ill or postoperative patient WITHOUT systemic toxicity or mucosal inflammation
• Mechanical large bowel obstruction (malignancy, volvulus, stricture) — Transition point on CT; not associated with mucosal inflammation
• Severe but uncomplicated colitis — Severe inflammation without colonic dilation ≥6 cm or systemic toxicity
• Hirschsprung disease (pediatric or adult variant) — Chronic constipation since infancy, narrow distal segment with dilated proximal bowel
• Diabetic gastroparesis / pseudo-obstruction — Long-standing diabetes, chronic motility disorder

Diagnostic workup

Diagnostic algorithm

flowchart TD
  A[Severe colitis<br/>+ systemic toxicity] --> B[Abdominal radiograph]
  B --> C{Transverse colon<br/>≥6 cm?}
  C -->|Yes| D[Toxic megacolon]
  D --> E[Resuscitate<br/>Stop antimotility drugs<br/>NPO, NG, broad-spectrum abx]
  E --> F[Treat underlying cause<br/>IV steroids if IBD<br/>Vanc/fidaxomicin if C. diff]
  F --> G[Surgical consult<br/>+ ICU + serial KUB]
  G --> H{Improving in 48-72 h?}
  H -->|Yes| I[Continue medical therapy]
  H -->|No / perforation / sepsis| J[Subtotal colectomy<br/>+ end ileostomy]

Treatment

Complications

• Colonic perforation (mortality up to 50%)
• Massive lower GI bleeding
• Septic shock and multiorgan failure
• Intra-abdominal abscess
• Need for emergent colectomy with long-term stoma
• Recurrent IBD activity, eventual need for restorative proctocolectomy with ileoanal pouch

PANCE pearls

• A patient with severe colitis whose stool frequency suddenly decreases is not improving — they may be developing toxic megacolon.
• Loperamide, opioids, and anticholinergics can precipitate toxic megacolon in active colitis — stop them immediately.
• Avoid colonoscopy and barium enema; serial plain films and CT guide management.
• Subtotal colectomy with end ileostomy and Hartmann pouch preserves rectum for future restoration — total proctocolectomy is generally avoided in the emergent setting.
• C. difficile is now a leading cause of toxic megacolon in nonsurgical hospitalized patients — always send a C. diff test.

References

• ACG 2019 — ACG Clinical Guideline: Ulcerative Colitis in Adults (Rubin et al., Am J Gastroenterol 2019)
• IDSA 2021 — IDSA/SHEA Clinical Practice Guidelines for Clostridioides difficile Infection (McDonald et al., Clin Infect Dis 2018/2021 update)
• ECCO 2022 — European Crohn's and Colitis Organisation guideline on severe ulcerative colitis