Cervical Spondylotic Myelopathy: Make the Difficult Diagnosis, Then Refer for Surgery

Cervical spondylotic myelopathy is different than many other problems associated with the spine and the back. While conservative medical management is usually the first treatment option for many of these conditions, early surgery is recommended for cervical spondylotic myelopathy. Evidence strongly suggests that performing surgery within 1 year of symptom onset is associated with a substantial improvement in neurologic prognosis. The challenge is to make the diagnosis, which is often difficult because of the variety of clinical signs and symptoms and the absence of any pathognomonic clinical findings. The onset of cervical spondylotic myelopathy is invariably insidious and commonly involves gait spasticity, followed by upper extremity numbness and the loss of fine motor control in the hands.

Pathophysiology
Cervical spondylotic myelopathy is the most common type of spinal cord dysfunction in patients older than 55 years and the most common cause of acquired spastic paraparesis in the middle and later years of life.(1,2) First defined in 1952 by Brain et al, (3) cervical spondylotic myelopathy is caused by narrowing of the cervical spinal canal due to congenital and degenerative changes. (4) The primary pathophysiologic abnormality is a reduced sagittal diameter of the spinal canal.

Mechanical Factors
White and Panjabi5 divide the mechanical factors involved in the pathogenesis of cervical spondylotic myelopathy into two groups: static and dynamic.

Static factors include:

•Congenital spinal canal stenosis (<13 mm anterior-posterior diameter)
•Disc herniation (Figure 1)
•Osteophyte formation in the vertebral bodies
•Degenerative osteophytosis of the uncovertebral and facet joints
•Hypertrophy of the ligamentum flavum and posterior longitudinal ligaments

Figure 1. Top, sagittal magnetic resonance imaging (MRI) of the cervical spine showing ventral spinal cord compression from disc herniation (white arrow) and vertebral body osteophytes (red arrow). Bottom, axial MRI of same spine showing large right-sided herniated disc (arrow) with reduction in cervical spinal canal diameter.

Dynamic factors are abnormal forces placed on the spinal column and spinal cord during flexion and extension of the cervical spine under normal physiologic loads. An example would be the trauma caused to the spinal cord by repetitively being compressed against an osteophytic bar during normal flexion and extension of the cervical spine.

Ischemia
Mechanical compression of neural elements is only one of the pathologic mechanisms that lead to cervical spondylotic myelopathy. Another is spinal cord ischemia, which happens when degenerative elements compress blood vessels that supply the cervical spinal cord and proximal nerve roots. Ischemia may result from three mechanisms: direct compression of larger vessels such as the anterior spinal artery, overall reduced flow in the pial plexuses and the penetrating small arteries that supply the cord, or impairment of venous flow, leading to venous congestion.

Pathologic findings that indicate that a vascular mechanism is the cause of cervical spondylotic myelopathy include spinal cord necrosis and cavitation in gray matter. The region of the spinal cord with the highest frequency of cervical spondylotic myelopathy (ie, C5 through C7) is also the area in which the vascular supply is the most tenuous. (4,6-8)

Cleveland Clinic Journal of Medicine
Volume 70, Number 10, October 2003