While Grade 1 is historically included in "remission" definitions, modern evidence suggests that Grade 0 (complete normalization) is associated with much lower rates of clinical relapse and a lower risk of colorectal cancer over time compared to Grade 1.
The Friability Rule
"Friability" (bleeding upon contact with the endoscope) is a hallmark of moderate disease (MES 2). If bleeding occurs without contact, it is automatically Grade 3.
Clinical Pearls
MES has poor inter-observer reliability in the Grade 0 vs. 1 distinction; UCEIS is often preferred for more granular research
Mucosal healing (MES ≤ 1) is a stronger predictor of long-term colectomy-free survival than simple symptom improvement
In clinical trials, a "remisison" usually mandates a Mayo subscore of 0 or 1 with no subscores > 1
Section 4
Next Steps
Management Action
01
MES 2 or 3: Failure to achieve mucosal healing. Trial of dose escalation or switch in biological mechanism.
02
MES 0: Therapeutic target met. Continue maintenance.
Complementary Scoring
Full Mayo Score for UC
UCEIS (Ulcerative Colitis Endoscopic Index of Severity)
Montreal Classification (UC)
Section 5
Evidence Appraisal
The Foundational Score
Coated oral 5-aminosalicylic acid therapy for mildly to moderately active ulcerative colitis.
Schroeder KW et al. • New England Journal of Medicine. 1987;317(26):1625-9. The primary description of the Mayo Clinic score.
Developed in Rochester, Minnesota, for the landmark ASacol trials. It was designed to provide an objective counterpart to the patient-reported outcomes (stool frequency and blood), which were considered too subjective for FDA regulatory approval.
