A Case of Lambert-Eaton Myasthenic Syndrome Presenting with Severe Autonomic Failure (P2.094)

Abstract

Objective: To describe a case of Lambert-Eaton Myasthenic Syndrome (LEMS) in a patient without weakness. Background: Clinical presentation of Lambert-Eaton Myasthenic Syndrome (LEMS) includes proximal muscle weakness, depressed deep tendon reflexes and autonomic dysfunction. As a paraneoplastic phenomenon, small cell lung cancers have been associated with LEMS. Design/Methods: A 61 year old Caucasian man presented with falls and dizziness for six months. Review of symptoms was notable for a 10-lb unintentional weight loss over one month before presentation. Past medical history was significant for chronic obstructive pulmonary disease and a 75-pack year smoking history. Exam revealed full strength in ocular, bulbar and limb muscles. Deep tendon reflexes were diminished, however normalized after exercise. Gait was wide-based initially without assistance; after a few steps he lost balance and required assistance. Results: Orthostatic vital signs revealed a > 50 mm Hg drop in systolic blood pressure without a compensatory change in heart rate. Autonomic testing demonstrated evidence of severe autonomic failure. Electrodiagnostic studies revealed severely reduced compound muscle action potential (CMAP) in the left ulnar nerve with 342% increase in CMAP amplitude after brief exercise. Repetitive nerve stimulation of the left spinal accessory nerve showed a baseline decrement of 16% and maximal decrement of 18% at 2 minutes post exercise, consistent with a pre-synaptic neuromuscular junction defect. Serological testing was remarkable for elevated P/Q and N-type calcium channel antibodies. Imaging studies revealed multiple pulmonary nodules for which pathology confirmed large cell neuroendocrine carcinoma. He was treated with plasmapheresis and immunoglobulin without improvement and transferred to medical oncology for initiation of chemotherapy. Repeat autonomic and electrodiagnostic studies 18 days after treatment were unchanged. Conclusion: This case illustrates that Lambert-Eaton Myasthenic Syndrome may manifest solely as severe autonomic failure and should be considered as a possible diagnosis in the described setting.

Disclosure: Dr. Chukwueke has nothing to disclose. Dr. Navalkele has nothing to disclose. Dr. Dieppa has nothing to disclose. Dr. Trivedi has nothing to disclose. Dr. Elliott has nothing to disclose. Dr. Vernino has received personal compensation in an editorial capacity for JAMA Neurology.