Myasthenia gravis associated with renal cell carcinoma: a paraneoplastic syndrome or just a coincidence

Background Myasthenia gravis (MG) can occur as a paraneoplastic phenomenon associated with thymoma. The association of MG with renal cell carcinoma (RCC) is not clear. Herein, we describe six cases of MG associated with RCC. Methods There were 283 patients diagnosed with MG admitted to our hospital from 2014 to 2019. Among them, 6 patients also had RCC. None of them had immune checkpoint inhibitor therapies. We performed a retrospective clinical data collection and follow-up studies of these 6 patients. Results These 6 patients with an average MG onset age of 61.3 ± 13.3 years, were all positive for anti-acetylcholine receptor antibodies. MG symptoms appeared after RCC resection in 3 cases. RCC was discovered after the onset of MG in 2 cases, and synchronously with MG in 1 case. After nephrectomy, the MG symptoms showed a stable complete remission in 1 case. Among them, four patients met the diagnostic criteria of possible paraneoplastic neurological syndromes. Conclusions Except for thymoma, patients with MG should pay attention to other tumors including RCC. MG may be a paraneoplastic syndrome of RCC, and further studies are needed to elucidate the relationship.