Tislelizumab-induced myositis antibody-negative myasthenia gravis in patients with urothelial carcinoma: a case report.

Tislelizumab, an immune checkpoint inhibitor, is widely used in the treatment of various malignancies; however, its immune-related adverse events(irAEs) require careful attention. Here, we report a case of a patient with recurrent urothelial carcinoma who developed myositis and myasthenia-like manifestations after receiving tislelizumab, despite negative myasthenia-associated antibodies. The patient's symptoms gradually alleviated following treatment with corticosteroids and intravenous immunoglobulin. To our knowledge, antibody-negative myasthenia gravis associated with tislelizumab has been scarcely documented. This case highlights that in patients receiving tislelizumab, early pharmacological intervention should be considered when typical myasthenia-like manifestations occur, even in the absence of antibody positivity, emphasizing the importance of prompt recognition and timely treatment.