known, although it is suspected that they represent unifocal, acute episodes of demyelination. Transverse myelitis is characterized by the acute onset of signs of spinal cord disease, usually involving the descending motor tracts and the ascending sensory fibers, suggesting a lesion at one level of the spinal cord. By enhanced magnetic resonance imaging, the apparent lesion in the spinal cord extends over many segments of the spinal cord. The annual incidence of transverse myelitis in Rochester, Minnesota, from 1970 to 1980 was 7.4 per 100,000 people (Beghi et al., 1982). The authors noted that this incidence is approximately sixfold higher than a rate calculated for Israel. They attributed this to differences in how successful the two studies were at identifying all cases of transverse myelitis.

Optic neuritis represents a lesion in the optic nerve behind the orbit but anterior to the optic chiasm. This cranial nerve is an extension of the central nervous system, and so when there is demyelinating disease, it represents central demyelination, not peripheral nerve demyelination. When the lesion is central to the orbit, the optic disk appears normal; this clinical form of optic neuritis is called retrobulbar neuritis. When the lesion or inflammation is very near the orbit, swelling of the optic disk can be seen on fundoscopic examination; this clinical form is called papillitis. This clinical distinction does not imply a different pathogenesis or pathology. Retrobulbar neuritis or papillitis in young adults is a very common early symptom of multiple sclerosis. Optic neuritis may occur as a solitary unexplained monophasic disease, and it may accompany the acute monophasic disease ADEM. No population-based incidence rates were identified.

Guillain-Barré Syndrome

Historical Background

Instances of acute ascending paralysis have been on record since the early nineteenth century, but it was the description by Guillain, Barré, and Strohl in 1916 of two cases (including cerebrospinal fluid findings) that was critical and discriminating enough to delineate a new syndrome. Those authors described acute areflexic weakness without fever, meningismus, or constitutional symptoms in two young infantrymen who both made a complete and rapid recovery. Using the newly introduced diagnostic technique of lumbar puncture, Guillain, Barré, and Strohl showed that the spinal fluid protein level was elevated but without an accompanying pleocytosis. These are the essential elements of GBS. Now, more than 75 years later, a great deal of descriptive and phenomenologic information has been added to the original observations, all of which indicate that this disorder is immune system mediated and targets peripheral nerves. Nevertheless, the critical

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