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

Abstract

Background: Transcranial magnetic stimulation (TMS) was utilized to study 7 patients who had undergone hemispherectomy for control of longstanding intractable epilepsy to assess cortical motor reorganization and MEP (motor evoked potentials) ipsilateral to the remaining hemisphere. Five patients were seizure-free post-operatively. All patients displayed a spastic hemiparesis, were able to walk, raise and bend the paretic arm and use the paretic hand to different degrees.Methods: We examined MEP threshold, site of maximal response to TMS, and latency to the biceps brachii, abductor pollicis brevis and the anterior tibial muscles using a 7 and 12 cm diameter round coil.Results: The following results were obtained: (1) No MEP could be induced to either side by use of the small coil. (2) When using the large coil MEP-threshold was elevated also when stimulating the non-affected hemisphere in comparison to normal controls. (3) Ipsilateral MEP were found to: be non-inducible in two patients, demonstrate largely increased latencies in 3 and be identical to contralateral MEP in two patients. (4) Ipsilateral MEP could be evoked more often in distal than proximal muscles. (5) The site of maximal ipsilateral MEP response was found approximately 2 cm anteriorly to that of the contralateral MEP to the non-affected side of the body (6) No correlation was found between the degree of hemiparesis and inducability of MEP.Conclusions: The pattern of reorganization of ipsilateral motor control following early brain damage and hemispherectomy appears to be extremely diverse and does not correlate with the degree of neurological impairment.