Classifications of rheumatological extraintestinal manifestations in inflammatory bowel disease: Unmet needs in clinical practice and trials

BACKGROUND: Rheumatological extraintestinal manifestations (EIMs) represent the most frequent complications of inflammatory bowel disease (IBD). Despite their clinical relevance, they remain heterogeneously defined and inconsistently assessed in both clinical practice and clinical trials. This narrative review aimed to summarize current evidence on the diagnostic assessment of IBD-associated rheumatological EIMs and to identify unmet needs for clinical evaluation and trial design. METHODS: A literature search was performed to identify studies evaluating the diagnosis and assessment of IBD-associated rheumatological EIMs. Data were extracted on diagnostic definitions, classification systems, outcome measures, and the use of patient-reported outcomes (PROs) across observational studies and randomized controlled trials. RESULTS: Substantial heterogeneity was observed in the diagnostic assessment of IBD-associated rheumatological EIMs, with inconsistent use of classification criteria and frequent reliance on nonstandardized clinical evaluation. No PRO instruments specifically developed or validated for IBD-associated rheumatological EIMs were identified. In randomized controlled trials, rheumatological EIMs were variably reported, with heterogeneous endpoints and limited structured assessment, particularly in phase 3 IBD trials. CONCLUSIONS: Evidence from this review reflects considerable methodological variability in the assessment of rheumatological EIMs in IBD. Standardized definitions, harmonized outcome measures, and the development of EIM-specific PROs are needed to support consistent endpoint selection and improve the evaluation of rheumatological outcomes in future clinical trials.