Colonoscopy Findings in Microscopic Colitis
Primary Endoscopic Appearance
The colon appears normal or near-normal on colonoscopic examination in microscopic colitis—this is the defining characteristic that distinguishes it from other forms of colitis and makes histologic diagnosis absolutely essential. 1
- The colonic mucosa is macroscopically normal or almost normal in appearance during colonoscopy, which is one of the three defining elements of microscopic colitis 1
- This normal endoscopic appearance occurs in approximately 83.5% of cases 2
Macroscopic Abnormalities (When Present)
When endoscopic abnormalities are visible, they occur in approximately 16.5% of cases and are typically mild and non-specific: 2
- Mild erythema (redness of the mucosa) 1
- Mild edema (mucosal swelling) 1
- Ulceration or linear scarring (more common in collagenous colitis specifically) 2
These findings are subtle and non-diagnostic, unlike the prominent features seen in ulcerative colitis (continuous inflammation with erythema, granularity, friability, ulceration, and spontaneous bleeding) or Crohn's disease (aphthous ulcers, deep serpiginous ulcers, and cobblestone appearance). 1
Critical Diagnostic Pitfall
Do not exclude microscopic colitis based on normal-appearing mucosa—this is the expected finding and biopsies are mandatory for diagnosis regardless of endoscopic appearance. 1
- The diagnosis of microscopic colitis absolutely requires histologic examination through colonic biopsies, regardless of what the mucosa looks like endoscopically 1
- Colonoscopy is the preferred modality over flexible sigmoidoscopy because microscopic colitis can have patchy distribution 3
Optimal Biopsy Strategy
To maximize diagnostic yield, specific biopsy locations and numbers are critical:
Biopsy Locations (in order of diagnostic value):
- Ascending colon: 96.9% diagnostic yield 4
- Transverse colon: 95.7% diagnostic yield 4
- Descending colon: 85.0% diagnostic yield 4
- Rectum: only 82.2% diagnostic yield 4
Recommended Biopsy Protocol:
- Take biopsies from both right colon (ascending and transverse) and left colon (descending and sigmoid), with a minimum of 2 samples from each segment, placed in separate containers 4
- A total of 6 biopsies should be taken: 3 from ascending colon and 3 from descending colon 5
- Biopsies from the rectum alone may give false negative results in 34-43% of cases 3, 4
- When both right- and left-sided biopsies are taken, 98.2% will show diagnostic features in both locations, but rectal biopsies alone are positive in only 88.7% 2
Special Considerations:
- If only flexible sigmoidoscopy is performed (not recommended), biopsies must be taken from the descending colon in addition to the rectum and sigmoid colon 4
- Biopsies should be taken from macroscopically normal mucosa, as normal appearance does not exclude microscopic colitis 4
- The terminal ileum can occasionally be involved, showing increased intraepithelial lymphocytes and even subepithelial collagen deposition in some patients 3