Mediastinal small cell cancer associated with Lambert-Eaton myasthenic syndrome: A case report

Lambert-Eaton myasthenic syndrome (LEMS) is typically characterized as a paraneoplastic syndrome associated with small cell lung carcinoma. The presence of LEMS in association with other neuroendocrine lung tumors, including carcinoids or large cell lung carcinoma, is highly unusual. The present case study reports the very rare case of a patient with mediastinal small cell cancer combined with LEMS. A 53-year-old man was admitted to the Bethune First Hospital with a 3-month history of weakness in the lower extremities that had become aggravated during the previous 20 days. A positron emission tomography-computed tomography (CT) examination demonstrated multiple enlarged, hypermetabolic lymph nodes between the vena cava and trachea, indicating the presence of inflammation. No other abnormalities were identified. A mediastinal lymph node biopsy revealed a high prevalence of small cell neuroendocrine carcinoma. The immunohistochemistry results were as follows: Ki-67 (+50, meaning that 50% of the cells exhibited Ki-67 expression), cytokeratin (CK; +), cluster of differentiation (CD)56 (+), synaptophysin (+), thyroid transcriptional factor-1 (+), epithelial membrane antigen (+), neuron-specific enolase (+), P63 (weakly +), leukocyte common antigen (-), CD99 (-), vimentin (-) and CK5/6 (-). Following a diagnosis of LEMS, the patient underwent one course of cisplatin + etoposide chemotherapy, which was ineffective. Subsequently, the patient underwent a different chemotherapy regimen (cisplatin + etoposide + ifosfamide), which significantly improved the symptoms of myasthenia. Following completion of this treatment regimen, the primary lesion was not observed on a lung CT scan, and the mediastinal lymph nodes had clearly diminished. Subsequently, the patient underwent two courses of radiotherapy (40 Gy/22f/6W).