Lambert-Eaton Myasthenic Syndrome Associated With Extrapulmonary Small Cell Cancer Detected by 18F-FDG PET/CT

A 46-year-old woman suffering from lower extremity weakness, dysarthria, dysphagia, dyspnea, and dry mouth was suspected of having Lambert-Eaton myasthenic syndrome based on the characteristic electromyographic abnormalities of right ulnar nerve, which demonstrated reduced resting compound muscle action potential amplitude and greater than 100% incremental change in high-frequency repetitive nerve stimulation. An F-FDG PET/CT was performed to detect the underlying neoplasm and revealed a retroperitoneal soft tissue mass with high F-FDG avidity in the left iliac fossa. The patient's symptoms were prominently relieved after the tumor resection, and the histopathology indicated a small cell carcinoma.