Serum ferritin predicts response to tocilizumab in glucocorticoid-resistant adult-onset Still's disease: a prospective real-world cohort study

ObjectiveTo evaluate the real-world effectiveness and safety of tocilizumab (TCZ) in glucocorticoid (GC)-resistant adult-onset Still's disease (AOSD) and explore predictors of clinical response. Methods This prospective, single-centre cohort study enrolled consecutive eligible patients with GC-resistant AOSD who initiated intravenous TCZ (4-8 mg/kg every four weeks) between June 2021 and June 2024. The primary outcome was clinical remission at 12 months per 2024 EULAR/PReS criteria (clinically inactive disease [CID] lasting ≥6 months).Secondary outcomes included CID rate at 6 months, laboratory and clinical activity scores, GC dose reduction, TCZ retention, and safety.Results Forty patients (median age 35.5 years; 80% female) were included.Clinical remission at 12 months was 55.0% (22/40); CID at 6 months was 62.5% (25/40).Significant improvements were observed in C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), serum ferritin (SF), and Pouchot scores (all p<0.001).Median daily prednisone dose decreased by 91%, from 50.0 mg to 4.4 mg (p<0.001).Baseline SF levels ≥ 2500 μg/L were independently associated with lower remission rates (adjusted odds ratio 0.19, 95% CI 0.04-0.94;p=0.042) and higher GC requirements at 12 months (β=5.55,95% CI 1.16-9.94;p=0.015).The 12-month TCZ retention rate was 65.0%.Serious adverse events included macrophage activation syndrome (MAS, 7.5%) and lymphoma (2.5%). Conclusion TCZ is effective and steroid-sparing in GC-resistant AOSD. Baseline hyperferritinaemia (SF ≥2500 μg/L) is apotential biomarker for poorer outcomes, suggesting a need for tailored management.