Stenosis and Neurologic Level Discrepancies in Cervical Spondylotic Myelopathy

Background Cervical spondylotic myelopathy (CSM) is the most common cause of cord dysfunction in older individuals. CSM involves either the upper motor neuron or lower motor neuron (LMN) in the cervical spine. The neurologic level of the LMN lesion does not usually correspond with the structural level detected via magnetic resonance imaging (MRI). Objective To examine the relationship between the structural level of stenosis and the neurologic level of LMN involvement in patients with CSM. Design Retrospective descriptive study. Setting Tertiary hospital. Patients Patients with cervical spondylotic myelopathy, aged 41-79 years. Methods We reviewed electromyography (EMG) and magnetic resonance imaging (MRI) findings from 17 patients with CSM to objectively show the relation between the structural level of stenosis and the neurologic level with LMN involvement. Main Outcome Measurements The structural level was defined by spinal canal stenosis with definite cord compression on MRI. The neurologic level was determined by myotomes with abnormal spontaneous activity on EMG. Results In all patients but one, myotomes with abnormal spontaneous EMG activity were one to 4 levels lower than the stenotic canal shown on MRI. Conclusions LMN involvement in CSM is usually not concordant with the structural lesion. For accurate diagnosis and treatment, physicians should recognize that myotomal involvement in CSM is often due to canal stenosis one to 4 levels above the lesion. Level of Evidence III