This multicenter retrospective real-world data study will evaluate the treatment pathways and disease burden of adult patients with Crohn's disease (CD) and ulcerative colitis (UC) treated in 5-10 Dutch hospitals between 2018 and 2026.

The study will assess:

• Treatment sequences, switching patterns, and treatment duration
• Prevalence and incidence of extra-intestinal manifestations (EIMs)
• Healthcare resource utilization (hospitalizations, outpatient visits, endoscopies, surgery, and length of stay)
• Direct healthcare costs
• Availability of disease activity biomarkers

Using linked administrative, prescription, procedure, and laboratory data, outcomes will be analyzed by age, line of therapy, and clinical characteristics. Special focus will be placed on the impact of EIMs on treatment patterns, healthcare utilization, and costs.

The findings will provide real-world evidence on IBD management in the Netherlands and support clinical decision-making, healthcare planning, and future research on treatment optimization and coexisting immune-mediated conditions.

Inflammatory bowel disease (IBD), comprising Crohn's disease (CD) and ulcerative colitis (UC), is a chronic, relapsing inflammatory disorder of the gastrointestinal tract with an increasing global burden. Patients frequently require lifelong management and may experience substantial healthcare resource utilization (HCRU) throughout the course of their disease. Beyond intestinal symptoms, many patients develop extra-intestinal manifestations (EIMs), including rheumatological, dermatological, ophthalmological, and pulmonary conditions, which further increase disease complexity and healthcare burden.

Over the past decade, therapeutic options for IBD have expanded considerably. In addition to conventional treatments such as corticosteroids, thiopurines, methotrexate, and aminosalicylates, multiple classes of advanced systemic therapies (ASTs) are now available, including anti-TNF agents, anti-integrin therapies, anti-IL-12/23 therapies, JAK inhibitors, and S1P receptor modulators. Despite these advances, long-term remission remains challenging for many patients, and there is limited real-world evidence describing how therapies are used in routine Dutch clinical practice, including treatment sequencing, treatment duration, healthcare resource utilization, and outcomes associated with EIMs.

This study aims to address these evidence gaps by generating real-world insights into treatment patterns, EIM burden, healthcare utilization, and costs among patients with CD and UC treated in Dutch hospitals. The findings are intended to support clinical decision-making, healthcare planning, and future research on IBD management in the Netherlands.

Study Design Retrospective, observational, multicenter real-world data cohort study using routinely collected healthcare data from 5 to 10 participating Dutch hospitals. The observational period runs from 1 January 2018 through 31 July 2026 and is fully closed prior to any data extraction. Data are extracted and pseudonymized within participating hospitals before transfer for analysis. No patient contact occurs and no additional data are collected.

Data sources include administrative and claims data, diagnosis registrations, prescription data, electronic prescribing system (EVS) data, laboratory databases, surgical and endoscopy activity data, and intramural medication records. Laboratory data may include fecal calprotectin (fCal), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), serum albumin, and therapeutic drug monitoring results.

Study Population Adult patients (≥18 years) receiving secondary hospital care with a diagnosis of Crohn's disease or ulcerative colitis, identified between January 2018 and July 2026. The index date is defined as the first confirmed CD or UC diagnosis, requiring at least one healthcare encounter for CD or UC and at least one prescription or dispensing record for an IBD-related medication. Patients who have objected to the use of their data for scientific research are excluded.

Main Research Question Among adult patients with Crohn's disease and ulcerative colitis treated in Dutch hospitals, what are the real-world treatment sequences, treatment duration, healthcare resource utilization, prevalence of extra-intestinal manifestations, and direct healthcare costs over time, and how do these vary according to age, line of therapy, and clinical characteristics?

Study Hypotheses Time-to-discontinuation differs between anti-TNF therapies and other advanced systemic therapy classes used as first-line treatment in patients with CD and UC.

Patients with one or more extra-intestinal manifestations have higher healthcare resource utilization than patients without extra-intestinal manifestations.

Availability and use of objective disease activity markers (fCal, CRP, ESR, and albumin) vary substantially between participating hospitals.

Objectives Primary Objective To describe real-world treatment sequences, treatment duration, healthcare resource utilization, prevalence of extra-intestinal manifestations, and direct healthcare costs among patients with CD and UC, stratified by age, line of therapy, and clinical characteristics.

Secondary Objectives To describe demographic and clinical characteristics of patients with CD and UC.

To quantify the prevalence and incidence of extra-intestinal manifestations. To characterize treatment pathways, treatment switching patterns, and healthcare resource utilization among patients with and without extra-intestinal manifestations.

To explore longitudinal changes in treatment patterns reflecting evolving therapeutic options.

Exploratory Objectives To assess the availability, completeness, and recording frequency of objective disease activity measures, including fecal calprotectin, CRP, ESR, and serum albumin.

To describe advanced therapy dosing patterns and surgical care pathways, including time from first surgery-related outpatient visit to surgery.

Statistical Analysis Analyses will be primarily descriptive. Patient characteristics, treatment pathways, treatment duration, prevalence and incidence of extra-intestinal manifestations, healthcare resource utilization, and costs will be summarized using appropriate descriptive statistics. Treatment duration and time-to-treatment discontinuation will be evaluated using Kaplan-Meier analyses. Treatment sequences will be visualized using Sankey diagrams where appropriate. Comparisons of healthcare utilization and costs between patients with and without extra-intestinal manifestations will be performed using matched descriptive cohorts. Analyses will be conducted using R and reported only for groups containing at least five patients to ensure privacy protection.

Ethical and Legal Framework The study uses retrospective pseudonymized patient data obtained from participating hospitals. Processing is conducted in accordance with the GDPR, including Article 9(2)(j) for scientific research purposes, Article 89(1) regarding appropriate safeguards, and Article 7:458 BW. The coding key remains exclusively under the control of the participating hospitals and is never accessible to LOGEX, investigators, or sponsors. Obtaining individual informed consent is considered impracticable due to the retrospective nature of the study and the large patient population. Patients retain the right to object to the use of their data through their treating hospital. Results will be presented exclusively in aggregated form with a minimum group size of five patients.

Dissemination Publication of study findings in peer-reviewed journals is the primary dissemination objective. Results will also be presented at scientific conferences and reported transparently regardless of the direction or magnitude of the findings. Publications will follow ICMJE authorship criteria and scientific independence will be safeguarded throughout the publication process.

Inclusion Criteria:

• Adult patients (≥18 years of age) who required secondary (hospital) care after January 2018 with a confirmed diagnosis of CD or UC, defined by at least one ICD-10 diagnosis code for CD or UC (K50, K51, K52).

Index date confirmation: the index date is defined as the first date of confirmed CD or UC diagnosis, requiring at least one healthcare encounter for CD or UC AND at least one prescription or dispensing record for any CD or UC-related medication within the observational period.

Exclusion Criteria:

• Patients who have formally objected to the use of their hospital data for scientific research purposes. Objections are recorded by the treating hospital in the DBC administrative system and automatically transferred to the research dataset, ensuring automatic exclusion from all analyses.

secondary and tertiary care, outpatient clinics