Longitudinal Registry of Difficult-to-Treat Inflammatory Bowel Disease

Difficult-to-treat inflammatory bowel disease (DTT-IBD) represents a heterogeneous group of patients with treatment-refractory, structurally complicated, postoperative, perianal, pouch-related, or psychosocially complex disease. This multicentre ambidirectional observational cohort will establish a longitudinal registry of adults with inflammatory bowel disease and systematically identify patients meeting prespecified DTT-IBD criteria. Clinical data will be reconstructed retrospectively and collected prospectively using a common data dictionary, including disease phenotype, advanced-therapy exposure and failure, objective disease assessments, multidisciplinary decision-making, treatment implementation, surgery, hospitalization, and long-term outcomes. The registry will characterize the occurrence, clinical domains, treatment trajectories, longitudinal disease-control states, and outcomes of DTT-IBD. No treatment, diagnostic test, dose, surgery, or monitoring procedure will be assigned by the study. Clinical management will remain entirely at the discretion of the treating physicians and patients. The platform is designed to support prespecified nested studies addressing treatment-failure mechanisms and clinical decisions, longitudinal DTT trajectories and cumulative uncontrolled disease, and implementation of multidisciplinary care.

Inclusion Criteria: * Age 18 years or older. * Established diagnosis of Crohn disease, ulcerative colitis, or inflammatory bowel disease-unclassified (IBD-U) based on clinical, endoscopic, imaging, and/or histopathological assessment. * Received longitudinal clinical care at a participating study center during the study period. * Availability of sufficient clinical information to establish the inflammatory bowel disease diagnosis and relevant longitudinal observation period. * Availability of sufficient patient identifiers and clinical dates to permit longitudinal record linkage and removal of duplicate records. * For participants included in the advanced-therapy longitudinal cohort, availability of a verifiable advanced-therapy exposure and treatment start date. * Eligible for inclusion under the ethics-approved retrospective and/or prospective cohort procedures, including informed consent or waiver of informed consent as applicable. Exclusion Criteria: * Inflammatory bowel disease diagnosis cannot be adequately confirmed. * Younger than 18 years at the time of cohort eligibility. * Clinical records cannot be reliably linked to a unique participant. * Insufficient clinical information to establish the relevant longitudinal timeline. * Prospective participant declines participation when informed consent is required.