The cases we have observed have been of the type that remained confined to several contiguous spinal segments, usually the upper abdomen and lower thorax as described by Brown and colleagues. Some patients report a premonitory sensation before the abdominal jerking, or there is worsening with the supine position. Whether these represent the same disease as the one noted above is unclear but the segmental, abdominal variety is now a firmly established entity, albeit also idiopathic, as described in a series by Roze et al and discussed under “Spinal or Segmental Myoclonus” in Chap. 4. The CSF may be normal or show a mild lymphocytosis and increase in protein content.
Myoclonic jerking of the trunk and limbs in a focal or segmental distribution is probably a result of neuronal damage of this same type that is limited to a few segments of the spinal cord. Clonazepan, various antiepileptic and antispasticity drugs in combination may partially suppress the myoclonus, and local injection of botulinum toxin has improved the symptoms in some. A similar syndrome in a few cases has followed vertebral or spinal artery angiography (see later). A paraneoplastic variety usually associated with breast cancer has been proposed, as in the case described by Roobol and colleagues, but its nature has not been fully elucidated.
In comparison with the brain, the spinal cord is an uncommon site of vascular disease. Blackwood, in a review of 3,737 necropsies at the National Hospital for Nervous Diseases, London, during the period 1903 to 1958, found only 9 cases of spinal cord infarction, but in general hospitals, the incidence (e.g., judged on clinical grounds in our hospital) is higher. The spinal arteries tend not to be susceptible to atherosclerosis, and emboli rarely lodge there. Of all the vascular disorders of the spinal cord, infarction as a result of aortic disease, dural fistula, bleeding, and arteriovenous malformation are the only ones that are encountered with any regularity, but even taken together, they are infrequent in comparison to demyelinating myelitis or compression of the cord by tumor. In current practice, most cases of infarction have developed in relation to operations on the aorta, usually the thoracic portion, where the vessel must be clamped for some period. The dural arteriovenous fistulas that cause spinal cord swelling are being recognized increasingly as their clinical syndromes are exposed and vascular imaging of small spinal arteries becomes more sophisticated. They have probably overtaken in frequency cord infarction in this category of disease. An understanding of these disorders requires knowledge of the blood supply of the spinal cord.
Vascular Anatomy of the Spinal Cord
The blood supply of the spinal cord is derived from a series of segmental vessels arising from the aorta and from branches of the subclavians and internal iliac arteries. The most important branches of the subclavian are the vertebral arteries, small branches of which give rise to the rostral origin of the anterior spinal artery and to smaller posterolateral spinal arteries that together constitute the major blood supply to the cervical cord. The thoracic and lumbar cord is nourished by segmental arteries arising from the aorta and internal iliac arteries. Segmental branches of the lateral sacral arteries supply the sacral cord.