Ultrasound-Proven Severe Synovitis Induced by PD-1 Inhibitor Therapy in a Patient Predisposed to Seronegative Inflammatory Arthritis

A 71-year-old Japanese woman was treated with programmed cell death protein-1 (PD-1) inhibitor, nivolumab, for renal cell carcinoma with lung metastasis. Although she had been treated with antirheumatic drugs from 40 to 60 years old by the diagnosis of seronegative inflammatory arthritis, treatment was discontinued based on her achievement of remission. She developed severe polyarthralgia after the administration of nivolumab. Severe synovitis with remarkable power Doppler signals was detected by ultrasound in multiple joints and tendons, and her serum levels of proinflammatory cytokine were remarkably elevated. Nevertheless, her arthritis disappeared after the discontinuation of nivolumab and treatment with a glucocorticoid without antirheumatic drugs. The use of PD-1 inhibitor may be restricted in patients predisposed to arthritis. Alternatively, a close monitoring of these patients by rheumatologists is necessary to identify predictable flares.