Cortical motor reorganization following early brain damage and hemispherectomy demonstrated by transcranial magnetic stimulation

Background: Transcranial magnetic stimulation (TMS) was utilized to study 7 patients who had undergone hemispherectomy for control of longstanding int ractable epilepsy to assess cortical motor reorganization and MEP (motor ev oked potentials) ipsilateral to the remaining hemisphere. Five patients wer e seizure-free post-operatively. All patients displayed a spastic hemipares is, were able to walk, raise and bend the paretic arm and use the paretic h and to different degrees. Methods: We examined MEP threshold, site of maximal response to TMS, and la tency to the biceps brachii, abductor pollicis brevis and the anterior tibi al muscles using a 7 and 12 cm diameter round coil. Results: The following results were obtained: (1) No MEP could be induced t o either side by use of the small coil. (2) When using the large coil MEP-t hreshold was elevated also when stimulating the non-affected hemisphere in comparison to normal controls. (3) Ipsilateral MEP were found to: be non-in ducible in two patients, demonstrate largely increased latencies in 3 and b e identical to contralateral MEP in two patients. (4) Ipsilateral MEP could be evoked more often in distal than proximal muscles. (5) The site of maxi mal ipsilateral MEP response was found approximately 2 cm anteriorly to tha t of the contralateral MEP to the non-affected side of the body (6) No corr elation was found between the degree of hemiparesis and inducability of MEP . Conclusions: The pattern of reorganization of ipsilateral motor control fol lowing early brain damage and hemispherectomy appears to be extremely diver se and does not correlate with the degree of neurological impairment. (C) 2 000 Elsevier Science Ireland Ltd. All rights reserved.