Stimulated single-fiber electromyography in Lambert-Eaton myasthenic syndrome.
The Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of neuromuscular transmission. Electrodiagnosis is confirmed by an increase in compound muscle action potential amplitude during high-frequency repetitive nerve stimulation or following brief exercise. We describe the results of stimulated single-fiber electromyography in 4 patients with disorders of neuromuscular transmission: LEMS (2), LEMS/myasthenia gravis (MG) overlap (1), and MG (1). Stimulated SFEMG was performed in the extensor digitorum communis muscle with axonal intramuscular suprathreshold stimulation at low and high rates. In all 4 patients, a rate dependence of jitter was found. In LEMS and LEMS/MG, jitter and blocking improved with high stimulation rates, as compared with the opposite effect in MG. We conclude that stimulated SFEMG is a valuable technique in the diagnosis of LEMS.
Chaudhry
V
V
Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD.
Watson
D F
DF
Bird
S J
SJ
Cornblath
D R
DR
D000368:Aged; D004576:Electromyography; D005260:Female; D006801:Humans; D015624:Lambert-Eaton Myasthenic Syndrome / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D009132:Muscles / Q000294:innervation*; D009157:Myasthenia Gravis / Q000175:diagnosis / Q000503:physiopathology; D009469:Neuromuscular Junction / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology