Differentiation Between Compressive Cervical and Thoracic Myelopathy Using the Central Motor Conduction Time Ratio

Purpose: Thoracic myelopathy is a rare condition whose diagnosis is often missed or delayed. This study aimed to differentiate between cervical and thoracic myelopathy using motor-evoked potential testing.
Methods: The authors included 835 patients with compressive cervical myelopathy and 94 patients with compressive thoracic myelopathy. Myelopathy using motor-evoked potentials were recorded from the bilateral abductor digiti minimi and abductor hallucis muscles through transcranial magnetic stimulation. The peripheral conduction time was measured through electrical stimulation of the ulnar and tibial nerves; moreover, the central motor conduction time (CMCT) was calculated by subtracting the peripheral conduction time from the myelopathy using motor- evoked potential latency.
Results: The most accurate differentiation between compressive cervical myelopathy and compressive thoracic myelopathy was achieved by the CMCT ratios (CMCT- ADM:CMCT-AH; cutoff value of 0.490, sensitivity of 83.0%, and specificity of 80.5%). After excluding patients with compressive cervical myelopathy who had spinal cord compression at C6-7, the cutoff value was 0.490, with a sensitivity of 83.0% and specificity of 87.3%.
Conclusions: Determining the CMCT ratio (cutoff value of 0.490) through motor-evoked potential testing could facilitate differentiation between compressive cervical myelopathy and compressive thoracic myelopathy.