Electrophysiological signs of changes in motor units after ischaemic stroke

Objective To study changes in motor units on the hemiparetic side, and the relationship between these changes and time after stroke onset and hemiparetic severity. Methods Neurography and concentric needle EMG were performed, and hemiparetic side mean and extreme parameter values were compared with the unaffected side mean and extreme parameter values using non-parametric tests. Results The mean M wave amplitude was significantly lower, while the spontaneous activity and the mean number of motor unit potential (MUAP) phases and turns were significantly higher on the hemiparetic side. The outliers above maximum for MUAP duration and amplitude on the hemiparetic side were significantly higher than those on the unaffected side. Correlations were found between the hemiparetic side parameter values and time after stroke onset and hemiparetic severity. Conclusions Axonal or neuronal lesion occurs and collateral reinnervation starts in the acute phase after stroke, while enlarged motor units are found in the chronic state. These changes correlate with hemiparetic severity. Significance This work confirms the controversial concept about lower motor neuron injury with stroke, and provides some information about its time course.