Motor Unit Number Estimates and Quantitative Motor Unit Potentials Analysis Associated with Motor Deficits in Carpal Tunnel Syndrome
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The purpose of this study was to determine the utility of decomposition-based quantitative electromyography (DQEMG) in detecting signs of motor unit loss and collateral sprouting in compression neuropathy. In order to accomplish this, needle- and surface-detected motor unit potential (MUP) morphological features, determined by DQEMG, were used to determine evidence of collateral sprouting. Evidence of motor unit loss was measured using motor unit number estimates (MUNEs). Six subjects with severe carpal tunnel syndrome (CTS), eight subjects with mild CTS and nine healthy individuals with no known neuropathy participated in this cross sectional study. All subjects completed two phases of data collection: 1) an examination consisting of physical and electrophysiological tests to assess the presence and/or severity of CTS and 2) quantitative electromyography techniques to record MUNEs and MUP morphological characteristics. The needle-detected MUP parameters included peak-to-peak amplitude, duration and number of phases. The presence of satellite potentials was also investigated in the needle-detected MUPs. The surface-detected MUP parameters examined included peak-to-peak amplitude, duration and negative peak area. Kruskall-Wallace tests were used to determine group differences for all outcome measures. The MUNEs were lower (p<0.017) in the severe CTS group as compared to those with mild or no CTS. This result suggests that individuals with severe CTS experience a decrease in the number of functioning motor units. Despite statistically similar surface-detected MUP morphology, there were significantly larger needle-detected MUP amplitudes (p<0.017) and satellite potentials (p<0.05) were present in the severe CTS group as compared to the mild CTS group and healthy control group. These findings suggest there is collateral reinnervation in individuals with severe CTS. The results of this study support the use of DQEMG in future studies of compression neuropathies as an effective means to document the progression of motor deficits.