About 10% of patients have features of both UC and Crohn’s Disease (CD); these patients are defined as having IBD unclassified (IBDU). Despite newer diagnostic tools, the frequency has not diminished over the past 30 years.
Indeterminate colitis describes the histological appearance of a colectomy specimen with features of both UC and CD.
The Montréal classification defines macroscopic disease distribution as proctitis (limited to the rectum), left-sided (distal to splenic flexure), and extensive. Macroscopic and microscopic extent are correlated poorly (κ=0.39).
Disease activity is defined as remission, mild, moderate and severe. In those with active colitis, severe colitis is defined by the Truelove and Witts criteria and mandates hospital admission for intensive medical treatment. Several activity indices define remission, mild and moderate colitis:
- the Mayo score is widely used in trials.
- The Baron score is a commonly used endoscopic score although interpretation of activity is inconsistent.
- The UC endoscopic index of severity (UCEIS) is validated and captures 88% of variability between endoscopists; the score ranges from 0 to 8.
The value of the different indices for the purpose of clinical trials is beyond the scope of the Consensus, but has been reviewed elsewhere. ECCO recognises the need to validate clinical and endoscopic scoring systems.
In clinical practice, remission describes stool frequency ≤3/d without bleeding or urgency, and correlates well with regulatory remission (no visible blood or endoscopic mucosal friability) so generally endoscopy is not required to demonstrate remission. Relapse usually manifests with rectal bleeding and an increase in stool frequency; sigmoidoscopy may be needed to confirm relapse.
Early relapse occurs within 3 months of achieving remission; frequent relapse occurs ≥2/yr; infrequent ≤1/yr. Continuous relapse refers to persistent symptoms without remission.
Steroid-refractory and steroid-dependent disease are consistent with Crohn’s disease definitions. Similar time points are used for immunomodulator-refractory colitis. Refractory distal colitis is defined by persistent disease despite ≥8 weeks combined oral and topical therapy.
Inflammation of the pouch following ileo-pouch anal anastomosis (IPAA) is called pouchitis, occurring in >50% patients by 10 years but in only 10% of all patients is pouchitis chronic.