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. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12883-021-02311-8.