A motor cortex excitability and gait analysis on Parkinsonian patients

Transcranial magnetic stimulation (TMS) parameters were recorded in a lower limb muscle and correlated with the gait parameters of 25 patients with Parkinson's disease (PD) with and without dopamine substitution treatment (DST) and 10 control subjects. Single and paired-pulse TMS were recorded in the tibialis anterior muscle (TA). Gait analysis was performed using a 3D motion analysis system. Parkinsonian patients (PP) did not differ from the control subjects (CS) in terms of relaxed motor threshold, active motor threshold (AMT), cortical silent period (CSP), motor-evoked potential (MEP) amplitude and area, or paired-pulse TMS with short interstimulus intervals (ISI). At longer ISIs, paired-pulse TMS showed that the amplitudes of the conditioned MEPs were lower in untreated PP than in CS. DST partially compensated for this difference. Gait analysis showed that the gait of PP undergoing no treatment was slower and the stride length shorter than normal. Both of these parameters improved under DST, however. Analysis of data obtained on all the subjects combined showed that both of the latter parameters were correlated with the paired-pulse MEP amplitude and area at longer ISIs. In PP, the cortical areas responsible for the lower limb movements seem to undergo intracortical facilitation (ICF) impairments, whereas the intracortical inhibition process is normal. The ICF level was found to be associated to the stride length and the velocity. The fact that only these two gait parameters were found to be dopa responsive indicates that dopaminergic treatment may improve gait disorders by restoring the ICF.