Neuromyelitis Optica Spectrum Disorders (NMOSD)

Neuromyelitis optica (NMO) is an autoimmune inflammatory disorder of the CNS with a predilection for the optic nerves and spinal cord, often with longitudinally extensive transverse myelitis (LETM) on MRI. The discovery of aquaporin-4 (AQP4)-immunoglobulin G (IgG), an antibody against the astrocyte water channel in the CNS, clearly identified NMO as a disease separate from MS. The high specificity of AQP4-IgG has permitted recognition of a wider spectrum of clinical and radiologic features related to NMO. Other sites of CNS involvement not restricted to the optic nerves or spinal cord have been described in AQP4-IgG-seropositive patients such as the diencephalon, brainstem, and brain hemispheric white matter. In anti-AQP4-IgG-seropositive patients, partial clinical (e.g., only myelitis) and MRI findings have been recognized, while conversely, NMO-like MRI findings and clinical features can occur in anti-AQP4-IgG-seronegative patients, sometimes with anti-MOG antibodies.The term NMO spectrum disorder (NMOSD) has been adopted to reflect the clinical, serological, and radiological diversity. Clinical features alone may be insufficient to diagnose NMOSD; cerebrospinal fluid (CSF) analysis and radiological techniques, in particular MRI, are required to exclude other disorders and reveal the characteristic optic nerve, spinal cord, and cerebral findings. The value of MRI in the diagnostic process is particularly relevant in patients who are anti-AQP4-IgG negative or when serologic testing is unavailable. This chapter gives special consideration to the value of clinical neuroradiology in the diagnosis of NMOSD and in the distinction from MS (with short segment lesions rather than LETM) and other immune-mediated inflammatory demyelinating diseases.