Magnetic transcranial stimulation: clinical interest of the silent period in acute and chronic stages of stroke.

There is little information on the silent period during facilitation of the target muscle at the acute stage of stroke and the ultimate clinical status. We studied 69 subjects with transcranial magnetic stimulation: 20 matched controls and 49 hemiparetic patients investigated 7 and 90 days after the stroke (D7, D90). We measured the silent period duration (SPD) in the first dorsal interosseous muscle at 10 and 100% of maximal voluntary isometric contraction (VIC). The SPD index (the ratio of SPD at VIC 100% by SPD at VIC 10%) at D7 was matched with the clinical outcome at D90. Two patterns of responses could be determined at D7. In the normal subjects and in 27 out of 32 patients who eventually recovered satisfactory function at D90, the SPDs were stable during facilitation (SPD index 100%). On the contrary, in 10 out of the 17 patients with a poor functional outcome, the mean SPD decreased when VIC was increased (SPD index 80%); besides, their muscle tone was significantly increased at D90. Similar patterns were still present in the patients at D90: the mean SPD indexes were not significantly different from D7. We conclude that in the early stage of stroke, a low SPD index appears to be correlated with the eventual occurrence of spasticity.