Cervical Spondylotic Myelopathy: A Common Cause of Spinal Cord Dysfunction in Older Persons
WILLIAM F. YOUNG, M.D., Temple University Hospital, Philadelphia, Pennsylvania
FIGURE 2. Dynamic mechanical factors in cervical spondylotic myelopathy. (Left) During flexion, the spinal cord is stretched over ventral osteophytic ridges. (Right) During extension, the ligamentum flavum may buckle into the spinal cord reducing space for the cord.
Cervical spondylotic myelopathy is the most common cause of spinal cord dysfunction in older persons. The aging process results in degenerative changes in the cervical spine that, in advanced stages, can cause compression of the spinal cord. Symptoms often develop insidiously and are characterized by neck stiffness, arm pain, numbness in the hands, and weakness of the hands and legs. The differential diagnosis includes any condition that can result in myelopathy, such as multiple sclerosis, amyotrophic lateral sclerosis and masses (such as metastatic tumors) that press on the spinal cord. The diagnosis is confirmed by magnetic resonance imaging that shows narrowing of the spinal canal caused by osteophytes, herniated discs and ligamentum flavum hypertrophy. Choice of treatment remains controversial, surgical procedures designed to decompress the spinal cord and, in some cases, stabilize the spine are successful in many patients. (Am Fam Physician 2000;62:1064-70,1073.)
Cervical spondylotic myelopathy (CSM) is the most common spinal cord disorder in persons more than 55 years of age in North America and perhaps in the world. As the number of older persons in the United States increases, the incidence of CSM will most likely increase. In a prospective study designed to more accurately define the incidence of CSM, 23.6 percent of 585 patients with tetraparesis or paraparesis admitted to a United Kingdom regional neuroscience center had CSM.1 The overall prevalence in this population is unknown.
Pathophysiology of CSM
Spondylosis refers to the degenerative changes that occur in the spine, including degeneration of the joints, intervertebral discs, ligaments and connective tissue of the cervical vertebrae. There are three important pathophysiologic factors in the development of CSM: (1) static mechanical; (2) dynamic mechanical; and (3) spinal cord ischemia.2Static mechanical factors result in the reduction of spinal canal diameter and spinal cord compression. With aging, the intervertebral discs dry out resulting in loss of disc height. This process puts greater stress on the articular cartilage of the vertebrae and their respective end plates. Osteophytic spurs develop at the margins of these end plates . Osteophytes stabilize adjacent vertebrae whose hypermobility is caused by the degeneration of the disc.3
The disc also calcifies, further stabilizing the vertebrae. Osteophytes increase the weight-bearing surface of the end plates and, therefore, decrease the effective force being placed on them. In addition to osteophytic overgrowth, the ligamentum flavum may stiffen and buckle into the spinal cord dorsally. Osteophytic overgrowth ventrally and, in some cases, buckling of the ligamentum flavum dorsally can cause direct compression of the spinal cord resulting in myelopathy (clinically evident spinal cord dysfunction). Symptoms are believed to develop when the spinal cord has been reduced by at least 30 percent.4
Dynamic mechanical factors relate to the fact that the normal motion of the cervical spine may aggravate spinal cord damage precipitated by direct mechanical static compression. During flexion, the spinal cord lengthens, thus stretching over ventral osteophytic ridges. During extension, the ligamentum flavum may buckle into the spinal cord causing a reduction of available space for the spinal cord
Spinal cord ischemia probably plays a role in the development of CSM, particularly in later stages.5,6 Histopathologic changes in the spinal cord consistent with ischemia have been observed in patients with CSM. However, the precise mechanism for spinal cord ischemia is not completely understood. Other factors associated with the development of spondylosis include heavy labor, posture and genetic predisposition.7,8Also, 70 percent of patients with Down syndrome have an increased incidence of spondylosis by 50 years of age.9