Microscopic Colitis Diagnosis and Characteristics

Endoscopic and Histologic Findings

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, as recommended by the European Crohn's and Colitis Organisation 1, 2
The colonic mucosa is normal or almost normal in appearance during colonoscopy, which is one of the three defining elements of microscopic colitis, according to the American Gastroenterological Association 1
When abnormalities are present, they are typically mild and non-specific, including mild erythema or edema, as noted by the National Comprehensive Cancer Network 3

The diagnosis of microscopic colitis absolutely requires histologic examination through colonic biopsies, regardless of endoscopic appearance, emphasizing the importance of biopsy in diagnosis, as stated by the American College of Gastroenterology 1
Do not exclude microscopic colitis based on normal-appearing mucosa - this is the expected finding and biopsies are mandatory for diagnosis, as guided by the European Society of Gastrointestinal Endoscopy 1, 2

Ulcerative colitis shows continuous inflammation with erythema, granularity, friability, ulceration, and spontaneous bleeding, in contrast to microscopic colitis, as described by the Crohn's and Colitis Foundation 4, 5
Crohn's disease demonstrates aphthous ulcers, deep serpiginous ulcers, and cobblestone appearance, distinguishing it from microscopic colitis, according to the American Gastroenterological Association 6
Infectious colitis typically shows erythema, erosions, ulceration, and luminal bleeding, differing from microscopic colitis, as noted by the Infectious Diseases Society of America 3

Colonoscopy is recommended over flexible sigmoidoscopy because microscopic colitis often has a patchy distribution throughout the colon, making full‑colonic visualization essential for accurate diagnosis. 7

Biopsies taken from the ascending colon provide the highest diagnostic yield (≈ 96 %).
Biopsies from the transverse colon also have a high yield (≈ 95 %).
The descending colon yields diagnostic tissue in about 85 % of cases.
Rectal biopsies alone have a lower yield (≈ 82 %).
*(These percentages are derived from the same study that supports the preferred modality.) 7

When biopsies are obtained solely from the rectum, false‑negative results occur in roughly 34 %–43 % of patients, underscoring the need for sampling from additional colonic sites. 7

Obtaining biopsies from both right‑side (ascending and transverse) and left‑side (descending and sigmoid) segments results in diagnostic features being identified in 98 % of cases across both locations.

The terminal ileum may occasionally exhibit microscopic colitis–related changes, such as increased intra‑epithelial lymphocytes and subepithelial collagen deposition, indicating that ileal biopsies can be informative in select patients. 8