Understanding cervical spondylotic myelopathy

Cervical spondylotic myelopathy (CSM) refers to impaired function of the spinal cord caused by degenerative changes of the discs and facet joints acquired in adult life. This is the most common disorder causing dysfunction of the spinal cord in the United States. Most patients with this condition are over 50 years of age, but the age of onset is variable depending on the degree of congenital spinal canal narrowing.

The process that leads to spinal cord compression is a result of cervical "arthritis" (also called cervical spondylosis), which is incompletely understood and likely has a number of causes. Factors that are thought to contribute to cervical spondylotic myelopathy include:

• Normal age-dependent changes of the intervertebral discs, most commonly manifest as osteophytes (bone spurs) at the margins of the vertebrae.

• Arthritis in the neck leading to facet hypertrophy (enlargement of the facet joints)

• Thickening of the ligaments surrounding the spinal canal, especially the ligamentum flavum, which parallels loss of disc height.

• Translational mechanical instability resulting in subluxation (or partial dislocation) of the vertebral bodies

• Congenitally small spinal canal, which renders the patient’s spinal cord more susceptible to compression for a given amount acquires canal encroachment

• Repetitive wear and/or 'trauma' leading to degenerative changes affecting the disc spaces and vertebral endplates

These changes in the cervical spine produce narrowing of the spinal canal itself, leading to thickening of the posterior longitudinal ligament and bone spur (osteophyte) formation compressing the spinal cord, most commonly at the C4-C7 levels. The end result is chronic compression of the spinal cord and nerve roots leading to impaired blood flow and neurological deficit resulting in frank damage within the spinal cord itself. A related condition that is more commonly being appreciated in non-Asians is Ossification of the Posterior Longitudinal Ligament (OPLL).

Symptoms of cervical spondylotic myelopathy
Patients with cervical spondylotic myelopathy often have the following symptoms:

• Weakness, numbness or clumsiness of the upper extremities (arms, hands, fingers)

• Altered walking ability perceived as either poor balance, weakness, heaviness or numbness in the legs.

• Painful, stiff neck

• Variable degrees of radicular arm pain

Though cervical spondylotic myelopathy is painless in more than 50% of patients, pain may be described as a stabbing, burning sensation or a persistent dull ache radiating throughout the arms to the forearms, at times to the fingers, associated with "pins and needles" paresthesias extending into the fingers. Patients often comment about dropping objects accidentally or having trouble fastening their clothes. If prolonged, there may be associated muscle wasting and overt loss of sensation to vibration, pinprick sensation, and pain and thermal sensation.

In addition, on examination, the doctor may notice increased resting tone of the arms and legs, focal weakness of muscles supplied by affected nerve roots, unsteadiness of gait, and abnormally brisk deep tendon reflexes. Coordination may be affected as well, including impaired fine finger movement, as well as difficulty with coordinated walking, such as seen with reverse tandem gait. Neck flexion may induce electrical-like sensations running down the spine (referred to as Lhermitte's phenomenon).

Progression of cervical spondylotic myelopathy
As the impairment to spinal cord function (referred to as "myelopathy") progresses, both legs weaken and become progressively spastic. Bowel and bladder sphincter control may then be altered. In advanced cases, gait will become progressively more difficult without aid by a cane or a walker.