Tenosynovitis Induced by an Immune Checkpoint Inhibitor: A Case Report and Literature Review

A 51-year-old man underwent second-line treatment for non-small-cell lung cancer (NSCLC) with the immune checkpoint inhibitor (ICI) pembrolizumab. On day 2 after two cycles of pembrolizumab, he presented with edema limited to the left third, fourth, and fifth fingers. Based on symptoms, laboratory results, and contrast-enhanced magnetic resonance imaging (MRI) findings, we diagnosed him with tenosynovitis. We prescribed oral prednisolone (0.5 mg/kg/day), and pembrolizumab was continued. Prednisolone immediately relieved the symptoms, and the tumor was still shrinking on day 21 after eight cycles of pembrolizumab. ICI-induced tenosynovitis was managed while continuing ICI usage, suggesting that 0.5 mg/kg/day prednisone might be effective for tenosynovitis without ICI cessation.