Neuromyelitis optica spectrum disorder refers to a syndrome characterized by recurrent optic neuritis and/or longitudinally extensive transverse myelitis. Having only been recently recognized to be a different clinical entity from multiple sclerosis, there are scant publications regarding appropriate anaesthetic and perioperative management of this disease.

Neuromyelitis optica spectrum disorder (NMOSD) is often described as an idiopathic, relapsing, severe demyelinating disease of the central nervous system (CNS) that preferentially affects the optic nerve and spinal cord, although more correctly the pathology reflects an inflammatory astrocytopathy with secondary demyelination. It has recently been recognized as a distinct disease process from multiple sclerosis [1], associated, in most, but not all patients, by the presence of an IgG antibody to aquaporin-4, a water channel found on CNS astrocytes [2]. Patients typically experience repeating bouts of optic neuritis and/or longitudinally extensive myelitis of three or more vertebral segments in length but an area postrema syndrome of sustained nausea and/or and hiccups due to medullary involvement is also recognised [3].

Recently, the diagnosis criteria for NMOSD have been expanded as AQP4-IgG seropositive status is no longer a requirement for NMOSD [4-6]:

Diagnostic criteria for NMOSD with AQP4-IgG:

1. At least 1 core clinical characteristic
2. Positive test for AQP4-IgG using best available detection method
   (cell-based assay strongly recommended)
3. Exclusion of alternative diagnoses

Diagnostic criteria for NMOSD without AQP4-IgG or NMOSD with unknown AQP4-IgG status:

1. At least 2 core clinical characteristics occurring as a result of one or more clinical
   attacks and meeting all of the following requirements
2. At least 1 core clinical characteristic must be optic neuritis, acute
            myelitis with l longitudinally extensive transverse myelitis lesions
            (LETM)
3. Disssemination in space (2 or more different core clinical     
            characteristics)
4. Fulfillment of additional MRI requirements, as applicable
5. Negative tests for AQP4-IgG using best available detection method, or testing
   unavailable
6. Exclusion of alternative diagnoses

Core clinical characteristics:

1. Optic neuritis
2. Acute myelitis
3. Area posterma syndrome: episode of otherwise unexplained hiccups or nausea and vomiting
4. Acute brainstem syndrome
5. Symptomatic narcolepsy or acute diencephalic clinical syndrome with NMOSD-typical diencephalic MRI lesions
6. Symptomatic cerebral syndrome with NMOSD-typical brain lesions

Additional MRI requirements for NMOSD without AQP4-IgG and NMOSD:

1. Acute optic neuritis: requires brain MRI showing (a) normal findings or only
   nonspecific white matter lesions, OR (b) optic nerve MRI with T2-hyperintense lesion or T1-weighted gadolinium-enhancing lesion extending over >1/2 optic nerve length or involving optic chiasm
2. Acute myelitis: requires associated intradmedullary MRI lesion extending over ³ 3
   contiguous segments (LETM) OR ³ 3 contiguous segments of focal spinal cord atrophy in patients with history compatible with acute myelitis
3. Area postrema syndrome: requires associated dorsal medulla/area postrema lesions
4. Acute brainstem syndrome: requires associated periependymal brainstem lesions

NMOSD is thought to represent less than 1% of all CNS demyelinating diseases in the Caucasian population, but 20-48% of CNS demyelinating disease in certain non-Caucasian populations, particular in Asia and Africa [7]. Since NMOSD has been shown to have a different pathophysiology than multiple sclerosis, NMOSD has been observed to behave differently. Immunomodulatory treatments that have been shown to help multiple sclerosis have been also shown to be ineffective in NMOSD, while the inverse is true as well [8].