This nationwide observational study emulates a target trial to compare the effect of tocilizumab versus methotrexate initiation on major adverse cardiovascular events (MACE) in patients with incident giant cell arteritis using the French National Health Data System (SNDS).

Study Design and Data Source This study is a retrospective nationwide cohort study using the SNDS database covering approximately 99% of the French population. We emulated a hypothetical randomized trial comparing two treatment strategies: initiation of tocilizumab versus methotrexate within 6 months after hospital discharge for incident giant cell arteritis. Eligible patients aged ≥50 years hospitalized for incident GCA between 2012 and 2024 were included.

Statistical Analysis A clone-censor-weight approach was used to account for treatment initiation timing and avoid immortal time bias. Inverse probability of censoring weights were applied to adjust for informative censoring. Treatment effects were estimated using weighted Kaplan-Meier methods and Cox proportional hazards models.

Outcomes The primary outcome was the occurrence of major adverse cardiovascular events (MACE), defined as myocardial infarction, ischemic stroke, or all-cause death. Secondary outcomes included individual cardiovascular components, aortic events, and major vascular relapse.

Regulatory Compliance This study was conducted using the SNDS through the permanent access granted to Assistance Publique - Hôpitaux de Paris (AP-HP), in accordance with French Decree No. 2016-1871 and French Public Health Code (Art. R. 1461-13 and 14). The study was registered in the AP-HP internal registry of research projects before initiation. In compliance with the GDPR and French regulations, individual informed consent was not required as all data were fully anonymized

Inclusion Criteria:

• Age ≥50 years Incident hospitalization for giant cell arteritis Initiation of tocilizumab or methotrexate within 6 months Received systemic corticosteroids ≥20 mg/day within 30 days following hospital discharge

Exclusion Criteria:

• Prior use of tocilizumab or methotrexate Age >90 years Length of stay >30 days Not discharged home Prior aortic disease or vascular imaging within 2 years Initiation of both treatments during grace period

Patients aged ≥50 years hospitalized for incident giant cell arteritis in France identified from the SNDS database.