Abstract Details

Title Abnormal Spontaneous Activity in Lambert-Eaton Myasthenic Syndrome

Topic Muscle Disease/Neuromuscular Junction

Presentation(s) P02 - (-)

Poster/Presentation
Number 205

Objective

Background BACKGROUND: Lambert-Eaton myasthenic syndrome (LEMS) is a rare, autoimmune, presynaptic disorder of neuromuscular transmission frequently associated with antibodies against the P/Q-type voltage-gated calcium channel.

Design/Methods DESIGN/METHODS: We report a case of seronegative LEMS in a young man presenting with subacute proximal weakness, where needle EMG showed markedly abnormal spontaneous activity.

Results RESULTS: Routine electrodiagnostic testing revealed diffusely low compound muscle action potentials (CMAPs) and normal sensory nerve action potentials. More than 100% increment in CMAP amplitude was observed in multiple nerves after ten seconds of maximal exercise. Repetitive nerve stimulation at 3 Hz showed an abnormal decrement. Needle EMG demonstrated frequent fibrillation potentials and positive sharp waves in multiple muscles, together with myopathic motor units which were unstable.

Conclusions CONCLUSIONS: We review the literature on needle EMG findings in LEMS, and identify additional reports of abnormal spontaneous activity in LEMS. Cases of LEMS presenting with subacute proximal weakness with marked fibrillation potentials and positive sharp waves on needle EMG can thus be confused with irritable myopathies. A high index of suspicion in such cases should prompt post-exercise testing and repetitive nerve stimulation to distinguish an irritable myopathy from Lambert-Eaton myasthenic syndrome. By analogy to botulism, we hypothesize that the fibrillation potentials and positive sharp waves in LEMS indicate effective denervation of muscle fibers due to severely impaired presynaptic neuromuscular transmission.

Authors/Disclosures
Gulmohor Roy, MD PRESENTER	No disclosure on file
Sarah Youssof, MD	No disclosure on file
Shane Raines	Shane Raines has received personal compensation for serving as an employee of 2b Analytics, LLC.

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