[A case of small cell lung carcinoma without apparent primary lesion accompanying Lambert-Eaton myasthenic syndrome].

A 58-year-old man complaining of increasing weakness of muscular leg strength, diplopia and ptosis was admitted to our hospital. An electromyogram (EMG) showed typical waxing phenomenon in response to high-frequency repetitive stimulation. A diagnosis of Lambert-Eaton myasthenic syndrome (LEMS) was made from his symptoms and EMG results. A chest CT showed mediastinal lymph node swelling. No abnormal mass was seen in either lung field. His serum levels of a P/Q-type anti-voltage-gated calcium channel (VGCC) antibody, Pro-GRP, and NSE were high. FDG-PET showed accumulation of FDG to the mediastinal and left inguinal lymph nodes. The left inguinal lymphadenopathy was pathologically diagnosed as metastasis of small cell lung carcinoma. No tumor could be detected by bronchofiberscopy. No other distant metastasis was detected by brain MRI, abdominal CT, or FDG-PET. After 6 courses of chemotherapy for SCLC, a partial response and reduction of symptoms were obtained. For assessment of indistinguishable neuropathic symptoms, the possible diagnosis of paraneoplastic syndrome, such as LEMS, and the fact that early treatment for primary disease was effective, should be considered.