Mucosal Appearance of Microscopic Colitis
The colon appears normal or near-normal on endoscopic examination in microscopic colitis, which is the defining characteristic that distinguishes it from other forms of colitis and makes histologic diagnosis essential. 1, 2
Typical Endoscopic Findings
The hallmark of microscopic colitis is the discordance between clinical symptoms and endoscopic appearance:
The colonic mucosa is normal or almost normal in appearance during colonoscopy, which is one of the three defining elements of microscopic colitis (along with chronic watery diarrhea and characteristic histology). 1
When abnormalities are present, they are typically mild and non-specific, including mild erythema or edema. 1
The normal endoscopic appearance occurs despite active chronic inflammation visible on microscopic examination. 1, 3
Macroscopic Findings When Present
While the classic teaching emphasizes normal appearance, recent evidence reveals that subtle macroscopic findings can occur:
Approximately 16.5% of patients with microscopic colitis demonstrate distinct macroscopic findings at colonoscopy, challenging the traditional view of universally normal mucosa. 4
Specific macroscopic features that may be observed include:
These findings, when present, are non-specific and cannot distinguish microscopic colitis from other conditions without biopsy. 4, 5
Critical Diagnostic Implications
The diagnosis of microscopic colitis absolutely requires histologic examination through colonic biopsies, regardless of endoscopic appearance. 1, 3, 6
Key Clinical Pitfalls:
Do not exclude microscopic colitis based on normal-appearing mucosa - this is the expected finding and biopsies are mandatory for diagnosis. 1, 2
Both right- and left-sided biopsies should be obtained, as 98.2% of patients have diagnostic features in both locations, though rectal biopsies alone may miss the diagnosis (only 88.7% positive). 4
The presence of chronic watery, non-bloody diarrhea with normal colonoscopy should immediately prompt consideration of microscopic colitis and trigger appropriate biopsies. 1, 2, 3
Contrast with Other Forms of Colitis
This normal endoscopic appearance sharply contrasts with other inflammatory conditions:
Ulcerative colitis shows continuous inflammation with erythema, granularity, friability, ulceration, and spontaneous bleeding. 1
Crohn's disease demonstrates aphthous ulcers, deep serpiginous ulcers, and cobblestone appearance. 1
Infectious colitis typically shows erythema, erosions, ulceration, and luminal bleeding. 1
The normal or near-normal appearance in microscopic colitis is therefore a distinguishing feature that should raise clinical suspicion when paired with appropriate symptoms, but should never delay biopsy acquisition. 1, 2, 7