Motor unit number estimation in the evaluation of focal conduction block.
Temporal dispersion and phase cancellation limit the utility of amplitude reduction in compound muscle action potential (CMAP) as a measure of focal conduction block but may not affect motor unit number estimation (MUNE). Hence, MUNE offers the potential of a specific measure of conduction block. We investigated the role of MUNE in 11 patients with ulnar neuropathy and conduction block at the elbow and also in 8 normal subjects. MUNE failed to detect motor unit dropout in the patient group because reduced values for surface-recorded motor unit potentials (SMUPs) were obtained at proximal locations, suggesting that focal compression selectively damages larger motor axons, an hypothesis that has support from animal studies. We conclude that, because MUNE is affected by the physiological characteristics of functional axons surviving the underlying pathological process, the utility of MUNE is limited to diseases in which the expected pathology affects motor axons uniformly.
Jillapalli
Devanand
D
Department of Neurology, SUNY Upstate Medical University, 750 East Adams Street, Syracuse, New York 13210, USA. jillapad@upstate.edu
Bradshaw
Deborah Y
DY
Shefner
Jeremy M
JM
D000200:Action Potentials / Q000502:physiology; D000328:Adult; D000368:Aged; D004558:Electric Stimulation; D004594:Electrophysiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation*; D009431:Neural Conduction / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*; D014459:Ulnar Nerve / Q000473:pathology / Q000503:physiopathology*; D017769:Ulnar Nerve Compression Syndromes / Q000175:diagnosis* / Q000503:physiopathology