G. Sarcoid myelitis (Chap. 31)
III. Myelitis of noninfectious inflammatory type (Chap. 35)
A. Postinfectious and postvaccinal myelitis
B. Acute and chronic relapsing or progressive multiple sclerosis (MS)
C. Neuromyelitis optica (subacute necrotizing myelitis, NMO, anti-MOG, Devic disease; longitudinally extensive myelopathy) due to antibodies against aquaporin (Chap. 35)
D. Myelopathy with lupus or other forms of connective tissue disease and antiphospholipid antibody
E. Paraneoplastic myelopathy and poliomyelitis (Chap. 30)
From this outline it is evident that many different and totally unrelated diseases are under consideration and that a general description cannot possibly encompass such a diversity of processes. Overall, myelitis caused by multiple sclerosis and postinfectious processes are the most common causes in practice. This was the case in the series collected by de Seze and colleagues (2001a); Nowak and coworkers reported a similar distribution. Many of the myelitides are considered elsewhere in this volume in relation to the diseases of which they are a part. Here it is only necessary to comment on the principal categories and to describe a few of the common subtypes.
Viral Myelitis (See Also Chap. 32)
The enteroviruses, of which Coxsackie and poliomyelitis are examples, herpes zoster, arboviruses such as West Nile and the equine encephalitic viruses, and HIV are the important members of this category. The enteroviruses in particular have an affinity for neurons of the anterior horns of the spinal cord and the motor nuclei of the brainstem (i.e., they are neuronotropic and cause a disease that can be generically termed poliomyelitis), and herpes zoster virus has a clear affinity for the dorsal root ganglia; hence the disturbances of function are in terms of motor and sensory neurons, respectively, not of spinal tracts. We have cared for several patients who have had destruction of anterior horn cells as a consequence of an enterovirus other than poliomyelitis virus (see further on). West Nile virus shows the same proclivity to damage anterior horn cells. The onset of these conditions is acute and takes the form of a febrile meningomyelitis. Although there are fever, systemic symptoms, and sometimes, cutaneous features (in the case of zoster), it is the nervous system disorder that is most significant. The patient suffers the immediate effects of nerve cell destruction, and some degree of improvement nearly always follows as some neurons recover. Later in life, possibly as the neuronal loss of aging reduces the number of anterior horns, there may be an apparent increased loss of strength in muscles originally weakened by poliomyelitis (“postpolio” syndrome).
Relatively infrequent examples of a more or less transverse myelitis caused by herpes simplex virus (HSV types 1 and 2), varicella-zoster virus (VZV), CMV, EBV, any of the hepatitis viruses, and SV70 virus (causing epidemic conjunctivitis) have been reported, some in patients with immunodeficiency states, mainly AIDS. The situation is complex clinically, as most of these agents may also elicit a postinfectious variety of myelitis, described further on in this chapter and in Chaps. 32 and 35. HSV type 2 and CMV infections may also produce an acute lumbosacral radiculitis with urinary retention (Elsberg syndrome). A few cases of zoster myelitis have shown evidence of extensive inflammatory necrosis of the spinal cord with involvement of sensory and motor tracts, causing acute paraplegic and tetraplegic transverse syndromes. Pleocytosis in the cerebrospinal fluid and isolation of the viral DNA from the cerebrospinal fluid confirm the diagnosis of a primary viral infection as discussed in Chap. 32.