IDENTIFICATION OF DISEASE SEVERITY DEFINITIONS FOR ULCERATIVE COLITIS AND CROHN’S DISEASE
Authors: Chou Chiahung , Mukherjee Richa , Sanchirico Marie , Jiang Jeanne , Dulai Parambir 
Published: January 2024

Abstract

BACKGROUND
Evidence suggests that, in patients with ulcerative colitis (UC) or Crohn’s disease (CD), those with moderate disease may achieve better outcomes with vedolizumab than those with severe disease. However, no consensus definition of moderate disease exists for UC or CD, as confirmed by a comprehensive literature review published in 2016.1 We aimed to identify definitions of disease severity for UC and CD in studies published since the approval of vedolizumab.

METHODS
The first stage of the research comprised a systematic literature review (SLR) that complied with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 statement and was registered prospectively with PROSPERO (CRD42023427948). Literature searches were conducted in Embase, MEDLINE, and the Cochrane Library databases on May 16, 2023 to identify publications from 2015 onwards. Title and abstract screening, followed by full-text review was undertaken by two blinded reviewers, with discrepancies resolved by a third reviewer. Data on disease severity indices and thresholds used to define mild, moderate, and/or severe disease were extracted from eligible primary publications.

RESULTS
Data were extracted from 119 eligible publications (Figure 1), of which 109 related to UC only, 7 to CD only, and 3 to both UC and CD. For UC, the most common disease severity index was Truelove and Witts’ criteria (N = 82), followed by Mayo score or one of its derivatives such as partial Mayo score or Mayo sub-score (N = 29), Lichtiger index (N = 9), Montreal classification (N = 4), Rachmilewitz score (N = 3), and Oxford criteria (N = 3). The definitions identified for mild and moderate disease were similar across studies; however, numerical thresholds used to define moderate and severe disease with Mayo score, partial Mayo score, and Lichtiger index overlapped (Figure 2). For CD, the Crohn’s Disease Activity Index (CDAI) (N = 6) was the most commonly used disease severity index, followed by the Harvey–Bradshaw index (HBI) (N = 2). Moderate disease was defined as a CDAI score of 200–450 or 220–450 or a HBI score of 8–16.

CONCLUSION
For UC, the thresholds used to define moderate disease were similar across studies but overlapped with those used for severe disease in some cases. Too few CD publications were identified to draw robust conclusions, likely due to the exclusion of those describing patients with mild-to-moderate or moderate-to-severe disease without further stratification in the title or abstract. A targeted literature review of publications reporting phase 3 clinical trials of drugs for UC or CD is ongoing; the thresholds of all measurements used to stratify the patient cohorts in these trials will be extracted to further understand the characteristics of patients with moderate disease.
1. Peyrin-Biroulet L, et al. Clin Gastroenterol Hepatol. 2016;14(3):348-354.e17.

Figure 1 PRISMA flow diagram.

Figure 2 Numerical ranges used to define mild, moderate, and severe disease for UC.