Comparing immune-checkpoint inhibitor-mediated inflammatory arthritis to polymyalgia rheumatica: a prospective cohort study

BACKGROUND: Immune checkpoint inhibitor (ICI)-related inflammatory arthritis occurs in approximately 6% of ICI-treated patients, and is often long-lasting. The clinical presentation is heterogeneous, and often loosely resembles either rheumatoid arthritis (ICI-IA) with peripheral presentation, or polymyalgia rheumatica (ICI-PMR) with predominant bilateral shoulder and hip pain and stiffness. Our objective was to compare clinical features, immunosuppressive treatment, and cancer outcomes between ICI-IA and ICI-PMR. METHODS: Data were extracted from the Rheumatology Adverse Events Due to Immunotherapy Observational Study multicenter prospective registry, regarding patients with rheumatologist-diagnosed ICI-IA or ICI-PMR and no preexisting primary IA/PMR. Clinical features were collected at the first visit in the registry. Multivariable logistic regression was used to compare second-line immunosuppressive drug utilization between groups. Kaplan-Meier curves were constructed to compare time of prednisone tapering to a dose of (1) 10 mg and (2) 5 mg from the baseline registry visit. Cox proportional hazard models were used to compare progression-free survival (PFS). Date of first cancer progression from arthritis onset was extracted based on documentation of imaging and/or pathology in the medical record. Patients with ICI-PMR were also compared with an independent cohort of patients with primary PMR. RESULTS: We analyzed 490 patients: 418 with ICI-IA and 72 with ICI-PMR. Compared with patients with ICI-IA, patients with ICI-PMR were older (70 vs 63 years old, p