Neuromyelitis optica spectrum disorder

Neuromyelitis optica spectrum disorders (NMOSD) are a spectrum of autoimmune diseases characterized by acute inflammation of the optic nerve (optic neuritis, ON) and the spinal cord (myelitis). Episodes of ON and myelitis can be simultaneous or successive. A relapsing disease course is common, especially in untreated patients.

The signs and symptoms of NMOSD depend on the neurologic structures the disease affects, and, to some extent, the antibodies involved.

The most common initial manifestation of the disease is inflammation of the spinal cord (myelitis). Myelitis causes spinal cord dysfunction, which can result in muscle weakness, paralysis in the limbs, lost or reduced sensation, spasms, loss of bladder and bowel control, or erectile dysfunction. The myelitis can be transverse, affecting an entire cross-section of the spinal cord, and showing bilateral symptoms.

The second most common initial manifestation of the disease is inflammation of the optic nerve and/or optic chiasm (optic neuritis, ON). ON may lead to varying degrees of visual impairment with decreased visual acuity, although visual field defects, or loss of color vision, may occur in isolation or prior to formal loss of visual acuity. Compared to idiopathic ON and ON due to multiple sclerosis (MS), ON due to NMOSD more often results in severe visual loss at onset, with bilateral involvement, and permanent visual deficits.

Less commonly than the spinal cord and optic nerve, NMOSD can affect the brain stem. Lesions in the brain stem or upper cervical spinal cord can cause respiratory insufficiency. Lesions in the area postrema of the medulla oblongata can cause vomiting or hiccups, as well as pain and tonic spasms. Additional brain lesions are common but often asymptomatic (though cognitive deficits, as well as depression, may be underdiagnosed sequalae). Lesions may also affect the diencephalon, mostly in Aquaporin-4–Immunoglobulin-G (AQP4-IgG) NMOSD.

Signs and symptoms usually follow a relapsing and remitting course, but occasionally can be progressive (monophasic). Deficits can be temporary or permanent, the latter especially in the absence of treatment.^{[citation needed]}

Fatigue is a common symptom, with studies showing that as many as 77% of people with NMOSD have fatigue. Fatigue has been found to correlate with quality of life in people with NMOSD.

NMO and multiple sclerosis (MS) can be similar in clinical and radiological presentation, and MS may very rarely present with an NMO-like phenotype (e.g. in patients with long-standing MS resulting in confluent spinal cord lesions mimicking the longitudinally extensive spinal cord lesions typically seen in NMO). In consequence, NMO was in the past wrongly considered a clinical variant of MS. However, NMO is not related to MS in the vast majority of cases and differs from MS substantially in terms of pathogenesis, clinical presentation, magnetic resonance imaging, cerebrospinal fluid findings, disease course, and prognosis.