Abstract
Disorders affecting the neuromuscular junction (NMJ) are among the most interesting and rewarding seen in the electromyography (EMG) laboratory. These disorders are generally pure motor syndromes that usually preferentially affect proximal, bulbar, or extraocular muscles. They are confused occasionally with myopathies. With knowledge of normal NMJ physiology, most of the abnormalities affecting the NMJ can be differentiated using a combination of nerve conduction studies, repetitive stimulation, exercise testing, and needle EMG. NMJ disorders can be classified into immune-mediated, toxic or metabolic, and congenital syndromes. They usually are distinguished by their clinical and electrophysiologic findings. All are uncommon, but among them, myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) are the disorders most often encountered in the EMG laboratory. Both are immune-mediated disorders. In MG, the autoimmune attack is postsynaptic; in LEMS, the presynaptic membrane is the target of attack. Every electromyographer must understand the electrophysiology of these disorders so that appropriate electrodiagnostic tests can be applied and the correct diagnosis is not overlooked.
Published Version
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