Evaluation of the Association between Neck Pain and the Trapezius Muscles in Patients with Cervical Myelopathy Using Motor Evoked Potential: A Retrospective Study

STUDY DESIGN: Retrospective study. PURPOSE: We aimed to use motor evoked potentials (MEPs) to examine the association of electrophysiological assessment of the trapezius muscle with neck pain. OVERVIEW OF LITERATURE: Previous reports on the association of neck pain with the trapezius muscle have focused on surface electromyograms and muscle oxygenation; however, to our knowledge, none of these studies included detailed data on MEPs. METHODS: The study included 100 patients with cervical myelopathy who underwent surgery at the National Center for Geriatrics and Gerontology in Obu, Japan from June 2010 to March 2013. Before the surgery, neck pain was evaluated using a Visual Analog Scale (a score ≥50 indicated neck pain and a score <50 indicated no neck pain). The preoperative cross-sectional areas of the trapezius muscles were measured with cervical magnetic resonance imaging sagittal T2-weighted images. Cranial stimulation under general anesthesia was used to derive the MEPs, enabling the measurement of latency and amplitude, using preoperative MEPs of the trapezius muscles. RESULTS: The MEP of the trapezius muscle in patients with neck pain had significantly shorter latencies than those in patients who did not have neck pain. However, there was no significant difference in the amplitude between patients with and without neck pain. However, this tended to be greater in patients with neck pain as compared to that in those without neck pain. The cross-sectional area of the trapezius muscle in patients with neck pain was significantly smaller than that in those who did not have neck pain. CONCLUSIONS: MEPs revealed electrophysiological abnormalities of the trapezius muscles in patients with neck pain, supporting a relationship of neck pain with the trapezius muscles.