Rheumatoid Arthritis Symptoms Diagnosed by Rheumatic Immune-related Adverse Events Caused by Nivolumab in a Patient with Esophageal Cancer.

This report described the case of a 70-year-old man who developed polyarthralgia after nivolumab treatment for recurrent esophageal cancer. Arthritis developed after initiating nivolumab therapy, and the patient tested positive for rheumatoid factor and anti-citrullinated peptide antibodies. The hand and elbow joints were already deformed, suggesting that he had had rheumatoid arthritis for several years and that the symptoms had only become apparent after nivolumab administration. This patient had rheumatoid arthritis, which was diagnosed as a nivolumab-induced rheumatic immune-related adverse event (rh-irAEs). Arthralgia during nivolumab administration can occur in rh-irAE cases. Patients should be assessed for autoimmune diseases before initiating immune checkpoint inhibitors.