Difficult Differential Diagnosis of Paraneoplastic Neuromuscular Diseases Associated with Small Cell lung Cancer: A Report of Two Cases.

Lambert-Eaton myasthenic syndrome (LEMS) is a paraneoplastic neurological syndrome complication of small cell lung cancer (SCLC). The clinical symptoms of LEMS overlap with those of myasthenia gravis (MG), leading to misdiagnosis. Herein, we report two cases of SCLC with LEMS-like disease that were difficult to distinguish from MG because of atypical electromyographic findings without waxing patterns on high-frequency stimulation. Both patients responded poorly to oral pyridostigmine and intravenous immunoglobulin, and were reported to be positive for the anti-P/Q-type voltage-gated calcium channel antibody characteristic of LEMS. Differentiating between LEMS and MG based on clinical symptoms and EMG findings can be difficult.