In addition to those disorders common to the brain, the spinal cord is subject to certain lesions because of its position or structure. A few of the more important are mentioned.
Spinal cord injury results from dislocations, fracture, or compression in many cases, but a special form, called spinal shock, may result from a severe blow without actual distortion of adjacent tissue. In this case, there is a temporary paralysis which gradually clears. In direct damage, the cord may be slightly, partially, or completely damaged at one or more levels. Typical motor and sensory losses follow, with a poor prognosis for recovery if the nerve tissue is severely injured.
A fairly common type of potential cord injury is seen in a number of cases of slipped disks, in which the inner, soft part of the vertebral column extrudes into the spinal canal. If this compresses the cord, functional loss of temporary or permanent degree can follow; more often, pressure is exerted on spinal roots so that pain, numbness, and some type of muscle weakness intervene.
Spinal cord tumors are not infrequent and most of these are of two types, the metastatic, from a primary source elsewhere in the body, and the tumors of the meninges or connective tissue related to the cord. The latter include neurofibromas, meningiomas, and gliomas, which occur most often. The signs and symptoms and the extent of damage relate largely to the physical compression of the cord at a particular level. See also Tumor.
A few of the more common congenital defects involving the cord include an unclosed neural canal, or spina bifida, and reduplicated or otherwise malformed cords, such as those caught in an external sac of other tissues, the meningomyelocoele.
Inflammations may result from known or unknown agents and in meningitis may involve primarily the coverings; in myelitis, the cord itself. The meningococcus, pneumococcus, streptococcus, tubercle bacillus, and other microorganisms frequently cause meningitis. The most widely known cause of myelitis, of course, is the poliomyelitis virus group.
An ill-defined group of disorders characterized by degeneration of nerve tracts or myelin sheaths of the cord is found more often than one would suspect. In these, some unknown or poorly understood mechanism causes the deterioration of cells and fibers so that function is altered, then lost, and the nervous tissue is either replaced by a scar or a softening of cystlike area remains. Multiple sclerosis, combined degeneration associated with pernicious anemia, Parkinson's disease, postinfectious encephalomyelitis, and syringomyelia are examples. See also Multiple sclerosis; Parkinson's disease; Spinal cord.
