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Electrodiagnostic evaluation of the neuromuscular junction

David H Weinberg, MD
Section Editor
Jeremy M Shefner, MD, PhD
Deputy Editor
John F Dashe, MD, PhD


Repetitive nerve stimulation (RNS) and single fiber electromyography (SFEMG) are important confirmatory tests for the diagnosis of disorders of the nicotinic neuromuscular junction, particularly for myasthenia gravis, Lambert-Eaton myasthenic syndrome, and botulism. This topic will review the basic principles of neuromuscular transmission and electrodiagnostic testing with RNS and SFEMG.

Other clinical aspects of neuromuscular junction disorders are reviewed separately. (See "Clinical manifestations of myasthenia gravis" and "Diagnosis of myasthenia gravis" and "Clinical features and diagnosis of Lambert-Eaton myasthenic syndrome" and "Botulism".)


The nicotinic neuromuscular junction is a complex, specialized structure incorporating the distal axon terminal and the muscle membrane that allows for the unidirectional chemical communication between peripheral nerve and muscle. It consists of the presynaptic nerve terminal, the synaptic cleft, and the postsynaptic endplate region on the muscle fiber. Acetylcholine serves as the neurotransmitter for voluntary striated muscle. The sections that follow provide a simplified summary of the morphology and neurophysiology of the neuromuscular junction that permits an adequate understanding of the electrodiagnostic testing principles (figure 1).

Morphology — The presynaptic region of the nicotinic neuromuscular junction consists of a specialized terminal nerve structure surrounded by Schwann cells. The presynaptic region includes voltage-gated calcium channels embedded in the nerve membrane, numerous mitochondria, and acetylcholine-containing synaptic vesicles. Each vesicle contains 5000 to 10,000 molecules of acetylcholine, known as a quantum [1,2]. The populations of vesicles behave as if they are divided roughly into three pools [3]:

The primary pool for immediate release


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Literature review current through: Sep 2016. | This topic last updated: Sep 13, 2016.
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