Diagnostic Approach for Colitis
The diagnosis of colitis requires a multidisciplinary approach combining clinical history, laboratory findings, endoscopy with multiple biopsies, and histopathological evaluation, with colonoscopy and histology being the gold standard for definitive diagnosis. 1, 2
Initial Evaluation
Clinical Assessment
- Assess for key symptoms:
- Diarrhea
- Rectal bleeding
- Abdominal pain
- Urgency
- Tenesmus
- Evaluate risk factors:
- Recent travel history
- Medication use
- Contact with infected individuals
- Family history of IBD
Laboratory Testing
- Complete blood count
- C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)
- Liver and renal function tests
- Iron studies
- Stool tests:
- Fecal calprotectin (excellent sensitivity but poor specificity) 1
- Stool cultures for infectious pathogens
- Clostridioides difficile toxin assay
- Ova and parasites examination
Endoscopic Evaluation
Colonoscopy Protocol
- Full colonoscopy with ileoscopy is recommended for initial diagnosis 1
- For acute severe colitis, use flexible sigmoidoscopy without bowel preparation 1
- Obtain multiple biopsies from different colonic segments:
Key Endoscopic Features to Assess
- Distribution pattern (continuous vs. segmental)
- Rectal involvement (present in most ulcerative colitis cases)
- Mucosal appearance:
- Erythema
- Loss of vascular pattern
- Granularity
- Friability
- Erosions/ulcerations
- Pseudopolyps
Histopathological Examination
Biopsy Processing
- Immediate fixation in buffered formalin 1
- Serial or step sectioning (2-3 tissue levels with 5+ sections each) 1
- Routine hematoxylin and eosin staining 1
Key Histological Features
- Basal plasmacytosis (highest predictive value) 2
- Crypt architectural distortion
- Mucosal atrophy
- Inflammatory infiltrate pattern
- Cryptitis and crypt abscesses
- Granulomas (suggestive of Crohn's disease)
Differential Diagnosis
Inflammatory Bowel Disease
- Ulcerative colitis
- Continuous inflammation starting from rectum
- Superficial mucosal involvement
- Crohn's colitis
- Skip lesions (in 40% of cases) 1
- Transmural inflammation
- Granulomas
Infectious Colitis
- Bacterial: Salmonella, Shigella, Campylobacter, E. coli O157:H7
- Viral: Cytomegalovirus (particularly in immunocompromised)
- Parasitic: Entamoeba histolytica
- C. difficile (check for pseudomembranes, though may be absent in IBD patients) 1
Other Causes
- Ischemic colitis (normal rectum, watershed areas involvement) 1
- Radiation colitis
- Medication-induced colitis
- Microscopic colitis (normal endoscopic appearance)
Classification and Severity Assessment
Disease Extent (Montreal Classification)
- E1: Proctitis
- E2: Left-sided colitis
- E3: Extensive colitis 2
Disease Severity
- Mayo Score (0-12):
Common Pitfalls and Caveats
Endoscopic underestimation: Endoscopic appearance may underestimate true disease extent, particularly in quiescent ulcerative colitis 1
Inadequate sampling: Diagnostic accuracy increases from 66% to 92% when segmental biopsies are taken rather than limited samples 1
Discordance between endoscopy and histology: In 25% of cases, chronic colitis can be diagnosed in biopsies from endoscopically normal-appearing mucosa 1
Infectious mimics: Always exclude infectious causes before confirming IBD diagnosis, as stool cultures are positive in only 40-60% of infectious cases 1
Acute severe colitis: Avoid full colonoscopy and bowel preparation in acute severe colitis; flexible sigmoidoscopy is safer 1
By following this systematic diagnostic approach, clinicians can accurately diagnose colitis, determine its etiology, assess disease extent and severity, and guide appropriate treatment decisions to improve patient outcomes.