Assessment of central motor conduction time in the diagnosis of compressive thoracic myelopathy.

STUDY

DESIGN

Prospective clinical study.

OBJECTIVE

The objective of this study was to investigate central motor conduction time (CMCT) values in patients with compressive thoracic myelopathy (CTM) and analyze its power to diagnose this condition.

SUMMARY OF BACKGROUND DATA: CTM is rare and its diagnosis is often difficult, when other spinal disorders such as cervical or lumbar degenerative spondylosis supervene. Measurement of CMCT following transcranial magnetic stimulation is a useful means to evaluate the electrophysiological functions of the corticospinal tract; however, there are few reports describing CMCT values among patients with CTM.

METHODS

Motor-evoked potentials following transcranial magnetic stimulation, and compound muscle action potentials and F-waves following electrical stimulation in the ulnar and tibial nerves were measured from the abductor digiti minimi (ADM) and abductor hallucis (AH) muscles in 20 patients with CTM, 92 patients with compressive cervical myelopathy (CCM), and 18 control subjects. The CMCT detected from the ADM (CMCT-ADM), the AH (CMCT-AH), and the CMCT-ADM/AH ratio (CMCT-ADM/CMCT-AH) were calculated.

RESULTS

The CMCT-AHs in patients with CTM were significantly longer than in control subjects, although there were no significant differences in the CMCT-ADMs. In contrast, both the CMCT-ADMs and CMCT-AHs in the CCM group were significantly longer than those of the control group. The CMCT-ADM/AH ratios in the CTM group were significantly lower than those of the other groups. Among the CTM and CCM groups, when the cutoff point of the CMCT-ADM/AH ratio was set at equal to or lower than 0.52, i.e., the mean CMCT-ADM/AH ratio in the control group, the odds ratio for CTM was 68.4 (95% confidence interval: 8.62-543; P < 0.001).

CONCLUSION

Our data showed a significant pattern of CMCT parameters and low CMCT-ADM/AH ratios in patients with CTM. The measurement of CMCT is valuable as a noninvasive technique for screening patients with CTM or CCM before magnetic resonance imaging.