Gochi_2025_AME.Case.Rep_9_127

BACKGROUND: Thymoma is a rare malignancy accounting for less than 2% of annual cancer diagnoses. While commonly associated with myasthenia gravis (MG), its association with Lambert-Eaton myasthenic syndrome (LEMS), a paraneoplastic syndrome typically linked to small cell lung cancer, is rare. Even rarer are cases with overlapping features of both syndromes. CASE DESCRIPTION: We report a 36-year-old postpartum Asian woman with overlapping clinical features of LEMS and MG attributed to her stage IVa thymoma, and minimally responsive to chemotherapy, thus requiring aggressive surgical debulking with cardiopulmonary bypass (CPB). She presented 2.5 weeks postpartum with dyspnea and right pleuritic chest pain. Computed tomography (CT) imaging demonstrated a >20 cm heterogeneous right pleural mass, and a separate 10 cm anterior mediastinal mass invading the superior vena cava (SVC) and innominate vein. Biopsy confirmed thymoma type B2. Further positron emission tomography (PET)/CT imaging showed no distant metastasis. The Multidisciplinary Tumor Board recommended neoadjuvant chemotherapy due to vascular invasion, followed by surgical resection. A month later, she developed worsening dyspnea, diplopia, dysphagia, and generalized extremity weakness with serologic testing positive for acetylcholine receptor (AChR) blocking antibodies. She was diagnosed with a paraneoplastic neuromuscular syndrome attributed to her stage IVa malignant thymoma. She was started on pyridostigmine, an acetylcholinesterase inhibitor, improving her symptoms. Restaging CT showed minimal response to chemotherapy, necessitating palliative debulking surgery, including right extrapleural pneumonectomy, thymectomy, SVC repair, and pericardial and diaphragm reconstruction. Pathology confirmed diffuse thymoma type B2 with R1 resection. She recovered uneventfully and underwent adjuvant radiation therapy, and remains disease-free on interval surveillance imaging. CONCLUSIONS: This rare case of stage IVa thymoma in a postpartum Asian woman with overlapping features of LEMS and MG highlights the role of acetylcholinesterase inhibitors for symptom management, and the role of aggressive radical debulking surgery with CPB, in a young, otherwise healthy patient.