Transcranial magnetic stimulation (TMS) has been used to describe cortical plasticity after unilateral cerebral lesions. The objective of this study was to find out whether cortical plasticity occurs after bilateral cerebral lesions. We investigated central motor reorganization for the arm and leg muscles in cerebral palsy (CP) patients with bilateral cerebral lesions using TMS. Seventeen patients (12 with spastic diplegia, 1 with spastic hemiplegia, and 4 with athetoid CP) and 10 normal subjects, were studied. On CT/MRI, bilateral periventricular leukomalacia was observed in all spastic patients with preterm birth. In two normal subjects, motor responses were induced in the ipsilateral tibialis anterior, but no responses were induced in any normal subject in the ipsilateral abductor pollicis brevis (APB) or biceps brachii (BB). Ipsilateral responses were more common among CP patients, especially in TMS of the less damaged hemisphere in patients with marked asymmetries in brain damage: in 3 abductor pollicis brevis, in 6 BBs, and in 15 tibialis anteriors. The cortical mapping of the sites of highest excitability demonstrated that the abductor pollicis brevis and BB sites in CP patients were nearly identical to those of the normal subjects. In patients with spastic CP born prematurely, a significant lateral shift was found for the excitability sites for the tibialis anterior. No similar lateral shift was observed in the other CP patients. These findings suggest that ipsilateral motor pathways are reinforced in both spastic and athetoid CP patients, and that a lateral shift of the motor cortical area for the leg muscle may occur in spastic CP patients with preterm birth.

Twenty hemiplegic patients were studied with transcranial magnetic stimulation (TMS). Motor evoked potentials (MEPs) of the biceps brachii (BB) and the abductor pollicis brevis muscles (APB) were recorded on both sides simultaneously. TMS was carried out with an 8-shaped coil over different scalp positions in the intact hemisphere. Bilateral MEPs of BB were elicited in patients with later childhood lesions as well as early lesion, but those of APB were only elicited in the latter (up to 2 years). In patients with prenatal or birth lesion on BB and in all patients on APB, cortical maps of MEP amplitude of paretic and non-paretic sides showed similar distributions. There were no remarkable differences in mean latency between both sides, and correlation coefficients of MEP amplitude between both sides were high in these patients. In patients with postnatal lesion on BB, MEP maps of both sides showed different distributions, ipsilateral MEP latencies were delayed and correlation coefficients were low. We suspect that ipsilateral MEPs after early lesion derive from axonal sprouting both in the proximal and the distal muscles. After postnatal lesion, other mechanisms of ipsilateral motor projection take place in the proximal muscles, but not in the distal ones.

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