What are the typical colonoscopy findings in a patient with immune colitis?

Colonoscopy Findings in Immune Checkpoint Inhibitor-Associated Colitis

Immune checkpoint inhibitor-associated colitis (immune colitis) most commonly presents as pancolitis (≥3 affected colonic segments in 68% of cases) with variable endoscopic severity, and ulcerations are present in approximately 32-37% of cases, though the grade of diarrhea correlates poorly with endoscopic severity. 1, 2

Key Endoscopic Features

Distribution Pattern

• Pancolitis is the predominant pattern, affecting ≥3 colonic segments in 68% of patients who undergo complete colonoscopy 1
• Unlike ulcerative colitis, immune colitis does not necessarily follow a continuous pattern and may show patchy involvement 1
• The rectum may or may not be involved, distinguishing it from classic ulcerative colitis which typically shows rectal involvement 3

Mucosal Appearance

• Ulcerations occur in 32-37% of cases and are a critical finding that predicts steroid-refractory disease 1, 2
• Deep histological ulcerations invading the submucosa are specifically associated with steroid-refractory disease and may warrant early infliximab therapy 2
• Edematous, friable mucosa with erythema is commonly observed 1
• Petechial hemorrhages may be present 3

Severity Assessment

• Endoscopic severity scores (Mayo score, van der Heide score) do NOT correlate well with the clinical grade of diarrhea, making colonoscopy essential for accurate assessment 1
• Patients with higher endoscopic severity scores, presence of ulcers, or pancolitis require infliximab more frequently (56% of cases needed infliximab for steroid-refractory disease) 1

Critical Diagnostic Considerations

When to Perform Colonoscopy

• Colonoscopy should be performed in all patients with grade 2 or higher diarrhea to guide treatment decisions 4
• Endoscopy typically occurs 6-8 weeks after ICI initiation when symptoms develop 4
• The poor correlation between symptoms and endoscopic findings makes colonoscopy mandatory for severity assessment rather than relying on clinical grading alone 1

Differential Diagnosis Pitfalls

The endoscopic appearance of immune colitis can mimic several other conditions that must be excluded:

• Infectious colitis (present in 38% of acute hemorrhagic colitis presentations) must be ruled out with stool studies 5
• Ischemic colitis typically shows normal rectum, sharply defined segments (especially sigmoid to splenic flexure), and longitudinal ulcerations—features that may overlap with immune colitis 3, 6
• CMV colitis in immunocompromised patients can show similar ulcerations and should be excluded with biopsies 3
• Clostridium difficile must be excluded in all cases 5

Histological Correlation

• Biopsies are essential to confirm the diagnosis and exclude other pathologies 5
• The presence of deep ulcerations on histology (invading submucosa) specifically predicts steroid-refractory disease, occurring only in steroid-refractory cases in one series 2
• Histological features alone do not correlate with diarrhea grade, reinforcing the need for combined endoscopic and histological assessment 1

Clinical Management Implications

Predicting Treatment Response

• Patients with ulcerations, higher endoscopic severity scores, or pancolitis are more likely to require infliximab (66% of severe cases are steroid-refractory) 1, 2
• Detection of deep histological ulcerations may warrant early application of infliximab rather than prolonged steroid trials 2
• All patients in reported series achieved complete remission, though 2% required surgery for severe complications 2

Common Pitfalls to Avoid

• Do not rely on diarrhea grade alone to determine treatment intensity—endoscopy provides critical additional information 1
• Do not delay colonoscopy in grade 2 or higher symptoms, as early identification of ulcerations can guide aggressive therapy 4
• Do not assume rectal involvement—immune colitis does not follow the same distribution rules as ulcerative colitis 3, 1
• Always exclude infectious causes before attributing symptoms solely to immune-mediated colitis 5, 4