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Lambert-Eaton myasthenic syndrome: Clinical features and diagnosis

David H Weinberg, MD
Section Editors
Lisa M DeAngelis, MD, FAAN, FANA
Jeremy M Shefner, MD, PhD
Deputy Editor
John F Dashe, MD, PhD


Lambert-Eaton myasthenic syndrome (LEMS) is an uncommon disorder of neuromuscular junction transmission with the primary clinical manifestation of muscle weakness. Knowledge of subtle clinical features and laboratory abnormalities that accompany LEMS permits the early identification of the disorder. Early recognition is particularly important because of its strong association with small cell lung cancer (SCLC). Although LEMS can occur at any point in the course of SCLC, it may serve as a marker for early disease.

This topic will review the pathophysiology, clinical features, and diagnosis of LEMS. Treatment and prognosis of LEMS is discussed separately. (See "Lambert-Eaton myasthenic syndrome: Treatment and prognosis".)


LEMS is a disorder of reduced acetylcholine (Ach) release from the presynaptic nerve terminals, despite normal ACh vesicle number, normal ACh presynaptic concentration, and normal postsynaptic acetylcholine receptors. Lambert and Elmqvist, through a series of elegant intracellular muscle recordings, found that patients with what is now called LEMS had the following unique features [1,2]:

Normal miniature endplate potential amplitude, demonstrating normal postsynaptic sensitivity to acetylcholine (ACh)

Markedly reduced evoked endplate potential amplitude, suggesting a significant reduction in ACh release

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Literature review current through: Nov 2017. | This topic last updated: Nov 30, 2017.
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