Neuromyelitis Optica Spectrum Disorders

Neuromyelitis optica (NMO) is an inflammatory demyelinating central nervous system disease. It has been classically defined as a monophasic, isolated co-occurrence of optic neuritis and transverse myelitis with uncertain relationship to multiple sclerosis. In the past decade, however, NMO has emerged as a distinct disorder associated with serum antibodies that target the astrocyte water channel aquaporin-4, distinguishing it from multiple sclerosis. The specificity of aquaporin-4 antibodies has led to appreciation of a wider spectrum of clinical and neuroimaging features, termed NMO spectrum disorders (NMOSD), than was encompassed by the classic NMO definition. Moreover, immunopathological studies have demonstrated that aquaporin-4 antibodies have pathogenic potential and that the disorder is a primary astrocytopathy with secondary demyelination. This chapter discusses the clinical definition and diagnosis of NMOSD and approaches to management, many informed by rapid advances in the understanding of NMO pathobiology.