Evaluation of descending spinal cord tracts in patients with thoracic cord lesions using motor evoked potentials recorded from the paravertebral and lower limb muscles.

We evaluated the function of the descending spinal cord motor tracts in patients, with and without spinal cord lesion, using motor evoked potentials. We studied 50 normal volunteers and 15 patients with thoracic lesions. The onset latency of the negative waves of motor evoked potentials for the thoracic spines was obtained, and the descending spinal cord conduction time was measured for the thoracic segments. In normal subjects, motor evoked potentials of paravertebral muscles recorded from T1-T2 to T5-T6 initially appeared as negative waveform with transcutaneous electrical stimulation over occipitocervical junction, although those from T6-T7 to T8-T9 were initially positive and those from more caudal sites were flatter. The motor evoked potential waveforms of tibialis anterior muscles evoked by electrical stimulation over the occipitocervical junction were markedly similar to those over the L1-L2. In patients with upper thoracic lesions, descending spinal cord conduction time from T2-T3 to T5-T6 was prolonged (p < 0.01). The descending spinal cord conduction time from T5-T6 to T11-T12 was also prolonged (p < 0.01) in patients with lower thoracic lesion. The descending spinal cord conduction time from T2-T3 to T11-T12 in patients with smaller motor function scores (<2) was significantly prolonged (p < 0.01) compared with normal subjects and patients with larger function scores. The methods of recording motor evoked potentials from paravertebral muscles with transcutaneous electrical stimulation over occipitocervical junction were useful for evaluating the level and motor function of thoracic cord lesions.