Quantitative assessment of myelopathy patients using motor evoked potentials produced by transcranial magnetic stimulation

Abstract

Motor evoked potentials (MEPs) study using transcranial magnetic stimulation (TMS) may give a functional assessment of corticospinal conduction. But there are no large studies on MEPs using TMS in myelopathy patients. The purpose of this study is to confirm the usefulness of MEPs for the assessment of the myelopathy and to investigate the use of MEPs using TMS as a screening tool for myelopathy. We measured the MEPs of 831 patients with symptoms and signs suggestive of myelopathy using TMS. The MEPs from the abductor digiti minimi (ADM) and abductor hallucis (AH) muscles were evoked by transcranial magnetic brain stimulation. Central motor conduction time (CMCT) is calculated by subtracting the peripheral conduction time from the MEP latency. Later, 349 patients had surgery for myelopathy (operative group) and 482 patients were treated conservatively (nonoperative group). CMCTs in the operative group and nonoperative group were assessed. MEPs were prolonged in 711 patients (86%) and CMCTs were prolonged in 493 patients (59%) compared with the control patients. CMCTs from the ADM and AH in the operative group were significantly more prolonged than that in the nonoperative group. All patients in the operative group showed prolongation of MEPs or CMCTs or multiphase of the MEP wave. MEP abnormalities are useful for an electrophysiological evaluation of myelopathy patients. Moreover, MEPs may be effective parameters in spinal pathology for deciding the operative treatment.

Fig. 1

The average MEP latency and CMCT in 831 patients. MEPs were prolonged in 711 patients (86%) and CMCTs were prolonged in 493 patients (59%)

Fig. 2

CMCTs from the ADM and AH in the operative group and nonoperative group. The average CMCT from the ADM and AH in the operative group is 10.8 ± 1.4 and 19.0 ± 2.0 ms, respectively. The average CMCT from the ADM and AH in the nonoperative group is 8.1 ± 0.4 and 16.9 ± 1.4 ms, respectively. CMCTs from the ADM and AH in the operative group are significantly more prolonged than in the nonoperative group (P < 0.05)

Fig. 3

The patient was an 81-year-old man. Magnetic resonance image (MRI) showing cord compression at T11/12 due to disc herniation (a T1-weighted sagittal image, b T2-weighted sagittal image, c T1-weighted axial image, d T2-weighted axial image). CMCT from the ADM was normal, but CMCT from the AH was prolonged (e MEP from ADM, f MEP from AH)

Fig. 4

The patient was a 71-year-old woman. MRI showing multiple-level cord compression at C3/4, 4/5, 5/6 (a T2-weighted sagittal image), and spinal cord tumor at T3 level (b T2-weighted sagittal image, c Gadolinium enhanced T1-weighted coronal image). CMCT from the ADM was normal, but CMCT from the AH was prolonged (d MEP from ADM, e MEP from AH)