Ipsilateral motor response--is it an artefact?

The lack of information about the ipsilateral motor response to cortical stimulation prompted the present study. Motor evoked potentials (MEPs) in 60 patients with acute stroke were recorded bilaterally. The patients' ages ranged between 24 and 83 years; 45 were males. Intracerebral haemorrhage was present in 23 and infarction in 37 patients. In none of these patients was an ipsilateral response recorded from the hemiplegic side when a contralateral response was absent. On the non-hemiplegic side in all these patients an MEP was recorded on both contralateral and ipsilateral cortical stimulation. Unrecordable MEPs became recordable in 6 patients after 1-15 months of stroke. In these patients MEP latencies on ipsilateral cortical stimulation were either identical to that on contralateral stimulation (2 patients) or within the range of normal intraindividual variation. On the basis of these results, it is concluded that the ipsilateral motor response in our study may be due to cross stimulation of the normal hemisphere and not through the uncrossed motor pathways. Our results should be interpreted in the context of the stimulation conditions employed. Further studies are recommended using more focal stimulation to minimise the spread of current.