Key result
Ambulatory SMA adults show higher MUAP amplitudes and firing rates versus non-ambulatory peers and healthy controls.
Why the study?
To evaluate whether decomposition electromyography (dEMG) MUAP amplitude and firing rate are altered in SMA, and whether dEMG parameters associate with strength, function, and traditional electrophysiological assessments.
Does decomposition electromyography reveal altered motor unit characteristics across severities of adult spinal muscular atrophy?
Cross-Sectional
Does decomposition electromyography reveal altered motor unit characteristics across severities of adult spinal muscular atrophy?
Decomposition electromyography provides a reliable, noninvasive measure of motor unit characteristics that reveals divergent patterns across disease severity in adults with SMA.
dEMG may stratify motor unit function by SMA severity; leaves open its value as a longitudinal biomarker.
OBJECTIVE: To test the hypotheses that decomposition electromyography (dEMG) motor unit action potential (MUAP) amplitude and firing rate are altered in SMA; dEMG parameters are associated with strength and function; dEMG parameters are correlated with traditional electrophysiological assessments. METHODS: Ambulatory and non-ambulatory adults with SMA on nusinersen and healthy controls were enrolled. MUAPs were decomposed from multielectrode surface recordings during 30-s maximum contraction of the abductor digiti minimi (ADM). Isometric strength, upper limb function, patient-reported function, and standard electrophysiologic measures of the ADM (compound muscle action potential [CMAP], single motor unit potential [SMUP], motor unit number estimation [MUNE]) were collected. RESULTS: dEMG MUAP amplitudes were higher in ambulatory versus control and non-ambulatory groups and were higher in controls versus non-ambulatory SMA. In contrast, dEMG firing rates were higher in ambulatory versus non-ambulatory and control groups but similar between non-ambulatory and control. dEMG parameters showed moderate to strong positive correlation with strength and function whereas CMAP and MUNE better correlated with function than strength. SMUP did not correlate with strength, function, or dEMG MUAP amplitude. dEMG parameters show overall good test-retest reliability. INTERPRETATION: dEMG provided reliable, noninvasive measure of MUAP amplitude size and firing rate and revealed divergent patterns across disease severity in adults with SMA. Firing rate enhancement, as seen in milder SMA, may provide a therapeutic avenue for improving function in more severe SMA, where firing rates appear preserved. MUAP amplitude size and firing rate, quantified with dEMG, may be promising monitoring biomarker candidates for noninvasive assessment of SMA.
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Kelly et al. (2023) conducted a cross-sectional in Spinal muscular atrophy. Spinal muscular atrophy severity vs. Healthy controls was evaluated on dEMG motor unit action potential (MUAP) amplitude and firing rate. Decomposition electromyography revealed that MUAP amplitudes and firing rates were higher in ambulatory adults with SMA compared to non-ambulatory patients and healthy controls.
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