Laboratory Studies
Cyanocobalamin (vitamin B-12) levels and a serum rapid plasma reagin may help distinguish metabolic and infectious causes of myelopathy from cervical spondylotic myelopathy. Metabolic and infectious conditions may coexist with cervical spondylosis, and, thus, an abnormal laboratory profile does not exclude cervical spondylotic myelopathy.
Imaging Studies
Although plain films of the cervical spine are the least costly and most widely available imaging modality, the imaging study of choice is MRI.
Although a narrow spinal canal with a sagittal diameter of 10-13 mm (as visualized on a plain radiograph) has been associated with a higher incidence of neurologic deficit and cervical spondylotic myelopathy, this measurement has become less important with the widespread availability of MRI. MRI allows direct visualization of neural structures and allows a more accurate estimation of the cord space.
Plain radiography can help assess the contribution of spinal alignment and degenerative spondylolisthesis to canal stenosis.
MRI is a noninvasive and radiation-free procedure that provides excellent imaging of the spinal cord and subarachnoid space and is a sensitive method for determining involvement of these by extradural pathology. MRI allows multiplanar imaging, excellent imaging of the neural elements, and increased accuracy in diagnosing intrinsic cord disease. It may detect pathology in the asymptomatic patient, or the pathology may be unrelated to the symptoms. In one report, 57% of patients who were older than 64 years had disk bulging and 26% of patients in this age group had evidence of cord compression on MRIs. [25] Some spondylotic changes (eg, small lateral osteophytes, midbody calcific densities) may be overlooked by MRI.
Overall, the advantages of MRI significantly outweigh its deficiencies, and thus it has become the standard diagnostic study for spondylotic disease. It has been demonstrated to be an accurate imaging modality in several studies. When surgical results were used as the criterion standard, agreement with MRI findings was found in 74% of cases, agreement with CT myelography in 84% of cases, and with myelography in 67% of cases. In one study, MRI was demonstrated to be 90% sensitive for the diagnosis of cervical stenosis, while CT myelography and CT scanning were 100% sensitive. [26]
Plain films of the cervical spine are an inexpensive way of assessing spondylotic disease in symptomatic patients. Cervical spine films can demonstrate disk-space narrowing, osteophytosis, loss of cervical lordosis, uncovertebral joint hypertrophy, apophyseal joint osteoarthritis, and vertebral canal diameter. The nearly universal presence of spondylotic radiographic changes in elderly patients (and the similar appearance of a cervical spine film in a symptomatic patient and an asymptomatic patient) allows the classification of an individual patient as having mild, moderate, or severe spondylotic changes.
CT scanning is another important imaging modality. Superior to MRI in its definition of bony anatomy, CT scanning better defines the neural foramina. CT scanning is often used to complement MRI and to provide additional bony detail to characterize a lesion responsible for neural encroachment.
Myelography is also useful for demonstrating nerve root lesions. Myelography demonstrates nerve root take off very well. [27] It is particularly useful in patients under going reoperation.
Some authors, however, report that CT myelography has a lower rate of false-positive results compared with conventional myelography. Some researchers have concluded that CT myelography provides additional data only when myelography results are positive—negative myelography findings followed by CT scanning in the case of suspected spondylosis is unlikely to show any clinically useful findings. [28]
Recently, dynamic CT myelography has been reported as useful in the surgical planning for patients with cervical spondylotic myelopathy, in some cases altering the surgeon's approach on the basis of dynamic findings. [29] Nevertheless, the exact role for dynamic imaging such as dynamic CT myelography and dynamic MRI remains to be determined.
Diffusion tensor imaging (DTI), a developed magnetic resonance technique, can aid in detecting intramedullary lesions. One study found that when DTI is performed along 6 noncollinear directions with single-shot spin echoplanar imaging (EPI) sequence, it clearly revealed the intramedullary microstructure and more lesions than conventional MRI. [30]
Other Tests
Electrodiagnostic studies are useful in many patients.
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Electromyography (EMG) can help diagnose cervical radiculopathy and, occasionally, identify cervical spondylotic myelopathy.
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EMG is useful in the study of radiculopathy because it demonstrates a close correlation with neuroimaging and operative findings.
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It also provides an anatomic distribution of abnormalities, thus facilitating the differential of cervical radiculopathy from other similar causes of radicular symptoms.
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EMG can help determine how long a lesion has been present. When using modern imaging techniques such as MRI, EMG can help clarify whether a lesion observed on imaging is the cause of nerve root pathology.
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In a patient with cervical spondylotic myelopathy, EMG can exclude specific syndromes of peripheral neuropathy rather than confirm cervical spondylotic myelopathy.
Somatosensory evoked potentials and cortical motor evoked potentials also may help evaluate spinal cord dysfunction, especially in timing intervention for the asymptomatic or minimally symptomatic patient with early cervical spondylotic myelopathy.
Histologic Findings
Histologic findings associated with cervical spondylotic myelopathy are greatest at the site of maximal compression. Changes in the gray matter range from consistent motor-neuron loss and ischemic changes in surviving neurons to necrosis and cavitation. Frequently, involvement of white matter is minimal, although it varies in degree. White matter changes, when they occur, are generally seen in the ventral inner portion of the dorsal column or in the lateral columns bordering the gray matter, with the anterior columns being only slightly damaged. Nongliotic necrosis is frequently described. Wallerian degeneration of posterior columns cephalad to the site of compression and of corticospinal tracts caudal to site of compression is frequent. Widespread proliferation of small, thickened, and hyalinized intermedullary blood vessels is frequently reported.
Many of these findings are similar to a pathological model of vascular occlusion. Extensive infarction of gray and white matter is associated with anteroposterior compression ratios of less than 20%. [11, 7] Based on a cadaveric study, the critical degree of anteroposterior compression necessary to induce histopathologic changes in the spinal cord has been suggested to be 30%. [31]
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A 48-year-old man presented with neck pain and predominantly left-sided radicular symptoms in the arm. The patient's symptoms resolved with conservative therapy. T2-weighted sagittal MRI shows ventral osteophytosis, most prominent between C4 and C7, with reduction of the ventral cerebrospinal fluid sleeve.
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A 48-year-old man presented with neck pain and predominantly left-sided radicular symptoms in the arm. The patient's symptoms resolved with conservative therapy. Axial gradient echo MRI shows moderate anteroposterior narrowing of the cord space due to a ventral osteophyte at the C4 level, with bilateral narrowing of the neural foramina (more prominently on the left side).
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A 48-year-old man presented with neck pain and predominantly left-sided radicular symptoms in the arm. The patient's symptoms resolved with conservative therapy. Axial CT scan at C5-6 demonstrates a large ventral osteophyte (see arrow). In addition, uncinate process hypertrophy is present bilaterally and the right neural foramen is narrowed.
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T2-weighted sagittal MRI of a 59-year-old woman who presented with a spastic gait and weakness in her upper extremities showing cord compression from cervical spondylosis, which caused central spondylotic myelopathy. Note the signal changes in the cord at C4-C5, the ventral osteophytosis, buckling of the ligamentum flavum at C3-C4, and the prominent loss of disk height between C2 and C5.
