C43-05 Hidden in Plain Sight: Unexplained Dyspnea Revealing Lambert-Eaton Myasthenic Syndrome

Abstract Introduction Lambert-Eaton myasthenic syndrome (LEMS) is a rare neuromuscular junction disorder characterized by impaired presynaptic release of acetylcholine due to autoantibodies against P/Q-type voltage-gated calcium channels (VGCCs), resulting in reduced postsynaptic depolarization. Up to 60% of cases occur as paraneoplastic syndromes, most commonly associated with small cell lung cancer (1). Associations with lymphoproliferative disorders are uncommon, with only isolated reports (2). Diagnosis relies on characteristic clinical findings, repetitive nerve stimulation on electromyography (EMG), and detection of anti-VGCC antibodies (1). Typical features include fluctuating fatigue, proximal muscle weakness, autonomic dysfunction, and ocular involvement. Case Report A 74-year-old male with prior liver (2009) and kidney (2024) transplants on chronic immunosuppression presented with four months of progressive exertional dyspnea, generalized fatigue, and dizziness. Dyspnea improved when supine and recurred with standing or minimal exertion. Physical examination showed left ptosis, fatigable diplopia, and paradoxical abdominal breathing, with otherwise normal pulmonary findings. Chest tomography showed left hemidiaphragm elevation, and fluoroscopy demonstrated paradoxical motion consistent with left hemidiaphragm paralysis. Electrodiagnostic testing with repetitive nerve stimulation was nondiagnostic; however, serum P/Q-type VGCC antibody was markedly elevated (70.7 pmol/L), supporting LEMS diagnosis despite inconclusive electrophysiology. Brain MRI revealed multiple enhancing intracranial and intraparenchymal lesions, and brain biopsy confirmed Ebstein-Barr virus-positive primary CNS post-transplant lymphoproliferative disorder (PTLD), lymphoplasmacytic lymphoma subtype. Immunosuppression was reduced as initial management, and the patient subsequently elected hospice care after multidisciplinary discussion. Discussion This case highlights a rare presentation of LEMS secondary to EBV-positive CNS PTLD in a transplant recipient. While most LEMS cases occur with small cell lung cancer as part of a paraneoplastic syndrome, it can also be associated with lymphoproliferative and autoimmune diseases. The patient’s marked exertional dyspnea despite normal oxygenation, normal chest imaging, and an unremarkable pulmonary examination underscores the importance of a careful neurological assessment. Recognition of subtle ocular signs prompted serologic testing, which led to the diagnosis of LEMS. In patients with unexplained dyspnea, a focused bedside neurological exam is essential when pulmonary findings are unrevealing. References: 1. Schoser, Benedikt et al. “Lambert-Eaton Myasthenic Syndrome (LEMS): A Rare Autoimmune Presynaptic Disorder Often Associated with Cancer.” Journal of neurology 264.9 (2017): 1854-1863. Web. 2. Argov, Zohar et al. “Lambert-Eaton Myasthenic Syndrome (LEMS) in Association with Lymphoproliferative Disorders.” Muscle & nerve 18.7 (1995): 715-719. Web. This abstract is funded by: none