Magnetic transcranial stimulation: dissociation of excitatory and inhibitory mechanisms in acute strokes.

Magnetic transcranial stimulation was applied to 12 normal subjects and 30 patients (24 acute and 6 chronic) with hemiparesis contralateral to an ischaemic stroke. In the 24 acute patients, the recordings were made at the 7th day on the contralateral first dorsal interosseous (FDI) muscle. We studied the amplitudes of the motor evoked potential (MEP) responses and the post-MEP silent period durations (SPD) at different levels of stimulation intensity (SI) and voluntary isometric contraction (VIC). The evolution of these parameters was matched to the clinical status of the 24 acute patients evaluated 7, 30 and 90 days after the stroke (D7, D30 and D90). Our results may be summarised as follows: (1) in all cases, the MEP-amplitudes increased with facilitation and SI; (2) in the normal subjects and in patients who did recover, the SPD augmented with stronger SI but was found to be independent on the strength of voluntary contraction; (3) in the acute patients with poor recovery, as well as in the chronic patients with spasticity, the SPD decreased with stronger VIC. It may be concluded that MEP-amplitudes and SPD patterns point out excitatory and inhibitory mechanisms which may be differently affected in cerebral injuries. The association between shortening of the SPD with increasing VIC of the target muscle and poor recovery of the stroke after 3 months could be a useful clinical test to predict eventual recovery early after a stroke.