Intact conduction of fastest corticospinal efferents is not sufficient for normal voluntary muscle strength: transcranial motor cortex stimulation in patients with tetraplegia.

Abstract

In six patients with chronic severe tetraparesis, caused by closed head injury (3 cases), basilar thrombosis (2 cases) or global hypoxia (1 case), responses of suprathreshold transcranial magnetic stimulation of motor cortex to thenar and abductor hallucis muscles on both sides were studied. Results showed in most patients normal thresholds and latencies (17 out of 24 latencies within normal +/- 2 S.D., 20 thresholds within normal +/- 1 S.D.) and amplitudes of even higher than normal values. Latencies or thresholds did not correlate with severity of pareses and were in marked contrast to the severe pareses of the muscles under investigation. Despite different etiology CT-scans showed diffuse atrophy of cerebral white matter as a common finding. It is concluded that intact descending corticospinal motor pathways are a necessary but not a sufficient condition for voluntary motor function.