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Neuromyelitis optica (NMO; Devic’s disease) is an aggressive inflammatory disorder characterized by recurrent attacks of ON and myelitis; the more inclusive term NMO Spectrum Disorder (NMOSD) has been proposed to incorporate individuals with partial forms, and also those with involvement of additional structures in the central nervous system (Table 437-1). NMO is more frequent in women than men (>3:1), and typically begins in adulthood but can arise at any age. An important consideration, especially early in its presentation, is distinguishing between NMO and multiple sclerosis (MS; Chap. 436). In patients with NMO, attacks of ON can be bilateral and produce severe visual loss (uncommon in MS); myelitis can be severe and transverse (rare in MS) and is typically longitudinally extensive (Fig. 437-1) involving three or more contiguous vertebral segments. Also in contrast to MS, progressive symptoms typically do not occur in NMO. The brain MRI was earlier thought to be normal in NMO, but it is now recognized that in many cases brain lesions are present, including areas of nonspecific signal change as well as lesions associated with specific syndromes such as the hypothalamus causing an endocrinopathy; the area postrema in the lower medulla presenting as intractable hiccoughs or vomiting; or the cerebral hemispheres producing focal symptoms, encephalopathy, or seizures. Large MRI lesions in the cerebral hemispheres can be asymptomatic, sometimes have a “cloud-like” appearance and, unlike MS lesions, are often not destructive, and can resolve completely. Spinal cord MRI lesions typically consist of focal enhancing areas of swelling and tissue destruction, extending over three or more spinal cord segments, and on axial sequences, these are centered on the gray matter of the cord. Cerebrospinal fluid (CSF) findings include pleocytosis greater than that observed in MS, with neutrophils and eosinophils present in many acute cases; OCBs are uncommon, occurring in <20% of NMO patients. The pathology of NMO is a distinctive astrocytopathy with inflammation, loss of astrocytes, and an absence of staining of the water channel protein AQP4 by immunohistochemistry, plus thickened blood vessel walls, demyelination, and deposition of antibody and complement.

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TABLE 437-1Diagnostic Criteria for Neuromyelitis Optica Spectrum Disorder

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