The muscles innervated by C7, C8, and T1, encompassing mainly the hand and forearm, are affected on one side or bilaterally, but almost always markedly asymmetrically. There are few or no fasciculations and no sensory changes; the painless loss of power and muscle bulk proceeds smoothly over several years, giving the impression of a degenerative condition. MRI or CT myelogram performed with the neck flexed, as described by Hirayama and Tokumaru, shows the cervical cord to be atrophic with signal changes in the anterior parts of the cord and confirms the diagnosis of compression by the buckled dura. We have examined several such patients and can corroborate their claim from observation of MRI with the patient placed in a flexed-neck position. Presumably, this configuration causes ischemia of the anterior gray matter, but this has not been proved. Others have reported the syndrome in the absence of this structural configuration (Willeit et al). Two of our young male patients had long swan-like necks. What is most important about this process is the degree of recovery afforded by ligamentous sectioning and by similar surgical approaches that accomplish decompression of the lower cervical cord.
Paget Disease of the Spine (Osteitis Deformans)
Enlargement of the vertebral bodies, pedicles, and laminae in Paget disease may result in narrowing of the spinal canal. The clinical picture is one of cord compression. The plasma alkaline phosphatase concentration is high, and the typical bone changes are seen in radiographs. Usually, several adjacent vertebrae of the thoracic spine are affected but other parts of the skeleton are also involved (see later), which facilitates diagnosis. Posterior surgical decompression leaving the pedicles intact is indicated if there is sufficient stability of the vertebral bodies to prevent collapse. Medical management includes the use of nonsteroidal anti-inflammatory drugs for persistent pain; calcitonin to reduce pain and plasma levels of alkaline phosphatase; and cytotoxic drugs such as plicamycin and etidronate disodium to reduce bone resorption.
The spinal cord is obviously vulnerable to any vertebral maldevelopment or disease that encroaches upon the spinal canal or compresses its nutrient arteries. Some well-known abnormalities are listed here.
Congenital Anomalies at the Craniocervical Junction
Of these, congenital fusion of the atlas and foramen magnum is the most common. McCrae, who described the radiologic features of more than 100 patients with bony abnormalities at the craniocervical junction, found this partial or complete bony union of the atlas and occipital bone in 28 cases. He also noted that whenever the anteroposterior diameter of the canal behind the odontoid process was less than 19 mm, there were signs of spinal cord compression. Fusion of the second and third cervical vertebrae is a common associated anomaly but does not seem to be of clinical significance. There is considerable crossover with the foreshortened neck of the Klippel-Feil syndrome mentioned below.
Abnormalities of the odontoid process These were found in 17 cases of McCrae’s series. There may be complete separation of the odontoid from the axis or chronic atlantoaxial dislocation (atlas displaced anteriorly in relation to the axis). These abnormalities may be congenital or the result of injury and are known causes of acute or chronic spinal cord compression and stiffness of the neck.
In all the congenital anomalies of the foramen magnum and the upper cervical spine there is a high incidence of syringomyelia. McCrae found that 38 percent of all patients with syringomyelia and syringobulbia showed such bony anomalies, but this is considerably higher than in our experience. All patients whose symptoms might be explained by a lesion in the cervicocranial region (particularly patients in whom MS and foramen magnum tumor are suspected) require careful radiologic examination.