Myasthenia gravis developing in a patient with CNS lymphoma

A patient was initially diagnosed with right basal ganglia lymphoma causing left hemiparesis. His disease was resistant to intravenous methotrexate, so he received radiation therapy with remarkable regression of the mass. However, 6 months after his initial diagnosis, he developed symmetric weakness of the proximal muscles. Electromyography was consistent with myasthenia gravis and anti-acetylcholine receptor antibodies were elevated. Treatment with pyridostigmine and corticosteroids improved his symptoms. The residual lymphoma was further treated with rituximab and temozolomide with complete resolution. Pyridostigmine and corticosteroids were stopped after 14 months of initiation with good results. Our case is the first case report of paraneoplastic myasthenia gravis developing in a patient with primary CNS lymphoma. The diagnosis of paraneoplastic myasthenia should be considered in patients with CNS lymphoma who develop muscle weakness and speech problems.