Immune checkpoint inhibitor-induced inflammatory arthritis vs rheumatoid arthritis: A comparative review.

Immune checkpoint inhibitors (ICIs) have transformed the therapeutic landscape of oncology but are frequently accompanied by immune-related adverse events (irAEs). Among these, ICI-induced inflammatory arthritis (ICI-IA) has emerged as the most common musculoskeletal toxicity, often mimicking rheumatoid arthritis (RA) in its clinical and imaging features. This narrative review synthesizes current evidence comparing ICI-IA with RA across epidemiology, pathophysiology, clinical presentation, imaging, treatment, and prognosis. While both entities share overlapping manifestations such as polyarthritis, synovitis, and joint erosions, ICI-IA is typically seronegative, arises subacutely after ICI initiation, and exhibits distinct immunopathologic signatures, including cytotoxic CD8+ T-cell predominance and unique B-cell alterations. ICI-IA may persist after ICI cessation, with chronic disease linked to improved oncologic outcomes. Therapeutic strategies require balancing arthritis control and preservation of anti-tumor immunity. Glucocorticoids and conventional disease modifying anti-rheumatic drugs (cDMARDs) are key players with proven safety and efficacy, whereas biologic therapies remain reserved for severe or refractory cases mainly due to cancer progression concerns. Furthermore, early rheumatology referral improves patient outcomes and reduces glucocorticoid exposure. Understanding the differences between ICI-IA and RA is essential for optimizing diagnosis, guiding individualized approach and applying precision medicine at the crossroads of oncology and rheumatology.