Motor-evoked potentials from various levels of paravertebral muscles in normal subjects and in patients with focal lesions of the spinal cord.

STUDY DESIGN

This prospective study includes normal control subjects and patients with focal lesions of the spinal cord investigated by transcranial magnetic stimulation.

OBJECTIVES

To establish a stable method to elicit motor evoked potentials from cervical to lumbar segmental levels and to apply the method that would allow the localization in patients with restricted cord lesion. Thirty-four healthy subjects (10 women, 24 men) and 17 patients with focal spinal lesions were admitted to this study.

SUMMARY OF BACKGROUND DATA

The focal cord lesions and injuries were previously evaluated by the records of lower limb muscles after cortical stimulation, but this method did not demonstrate the vertebral levels at which the lesions were located.

METHODS

The paravertebral myotomal-evoked potentials were recorded in different segmental levels (T1, T6, T12, and L3) from paravertebral muscles, using surface and needle electrodes by transcranial magnetic stimulation in normal control subjects and patients.

RESULTS

In normal control subjects, paravertebral myotomal-evoked potentials were obtained from T1, T6, T12, and L3 paravertebral muscles with both recording techniques (surface and needle electrode). From T1 to L3 latencies of paravertebral myotomal-evoked potentials increased gradually (from 10 msec to 17 msec) in normal control subjects. The levels of spinal cord lesions were obtained reliably in 14 of 17 patients with thoracic-lumbar spinal cord lesions, by using both electrophysiologic methods. In 11 of 14 patients, the lesions produced total conduction block, at and below the lesion level. In the remaining 3 patients slowing of intersegmental conduction was observed along the focal cord lesion.

CONCLUSIONS

The paravertebral myotomal-evoked potentials obtained by surface electrode from paravertebral muscles and by midline needle electrode in the intrinsic rotatory muscles of the spine were useful in localizing lesions in the spinal segments in most of the patients with thoracic-lumbar cord lesions.