Introduction to Neuromyelitis optica (NMO)

  • Neuromyelitis optica (NMO) is an acute or subacute demyelinating lesion that occurs simultaneously or sequentially in the optic nerve and spinal cord. The disease was first described by Devic (1894), whose clinical features were monocular or binocular blindness with acute or subacute onset, with traversal or ascending myelitis associated with a few days or weeks before or after it. Known as Devic disease or Devic syndrome. The data show that NMO accounts for 1%-22% of all demyelinating diseases, the proportion in Western countries is low, and the proportion of non-Caucasians is high.

     

    Disease classification

    Optic neuromyelitis

    (1) Single-phase disease course NMO: 10-20%, relatively common in Europe, lesions are limited to the optic nerve and spinal cord, optic neuritis mostly bilateral and simultaneous involvement with myelitis at the same time or similar (within 1 month), neurological function Obstacles are often heavier than recurrent NMOs. But the survival period is longer.

    (2) Relapsing NMO: 80%-90%, relatively common in Asia, early manifestations of simple isolated optic neuritis or isolated myelitis, only about 10% of patients first affected optic nerve spinal cord at the same time

    (3) Progressive NMO: rare.

     

    Optic neuromyelitis lineage disease

    There are some non-specific inflammatory demyelinating diseases with similar pathogenesis to NMO, and the NMO-IgG positive rate is also higher. Wingerchuk summarized and proposed the concept of neuromyelitis optica Spectrum disorders (NMOSDs). In 2010, the European Union of Neurology (EFNS) clearly defined NMOSDs, specifically a group of potential pathogenesis similar to NMO, but clinical limitations, not fully consistent with NMO diagnosis related diseases.

     

    (1)2010 EFNS NMOSDs

    1 types of affected sites, such as 1ngitudinally extensive transverse myelitis (LETM), recurrent isolated optic neuritis (RION) and bilateral optic neuritis (B0N).

    2 NMO that occurs in the context of organ-specific or non-organ-specific autoimmune diseases.

    3 Atypical cases with symptomatic or asymptomatic brain lesions.

    4 optic-medullary MS (OSMS) in Asian countries.

    (2) 2007 Wingerchuk NMOSDs

    1 NMO.

    2 lesions are limited to the optic nerve and spinal cord.

    1. a) idiopathic single-phase or recurrent long-segment transverse inertial myelitis (MRI lesions ≥ 3 vertebral segments).
    2. b) Optic neuritis: recurrent optic neuritis or concurrent bilateral optic neuritis.

    3 Asian type of optic nerve spinal cord multiple sclerosis (OSMS).

    4 optic neuritis or long-segment transverse inertial myelitis combined with autoimmune diseases.

    5 optic neuritis or myelitis combined with NMO features of intracranial lesions (hypothalamus, corpus callosum, periventricular and brain stem).

    One study showed that 55% of NMO-IgG-positive patients with transverse myelitis relapsed or developed NMO within 1 year.

    Etiology and pathogenesis

    The cause is still unclear.

    AQP4 is the major aquaporin of the central nervous system, located on the foot processes of astrocytes. AQP4 is the main target of NMO-IgG, which explains that the lesions of NMO are mainly located in the optic nerve and spinal cord. AQP4 antibodies enter the central nervous system through a fraction of the blood-brain barrier that passes through the astrocytes and cause cell-dependent cytotoxicity. Astrocyte foot processes are degraded by NMO-IgG and complement, which in turn activates Macrophages, eosinophils, and neutrophils produce cytokines, oxygen free radicals, etc. that cause vascular and parenchymal damage, ultimately leading to damage to white matter and gray matter, including axonal and oligodendrocytes.

    Familial NMO cases are rare and are less than 3% of all confirmed NMOs. Human leukocyte antigens DPB1*0501 (Asian population) and DRB1*0301 (Caucasian population) were associated with NMO susceptibility. Explain that heritage factors play a role in the pathogenesis of NMO.

     

    Pathophysiology

    NMO lesions mainly involve the optic nerve, optic chiasm and spinal cord (thoracic and cervical segments). Its pathological changes are related to the survival of NMO patients.

    Spinal cord pathology

    (1) Gross pathology: Generally, multiple spinal cord segments are involved, usually from the chest to the cervical or lumbar spinal cord. In the early fatal cases, the spinal cord may be swollen and softened; in patients with longer survival, the spinal cord may shrink.

    (2) Pathology under the microscope: The spinal cord swelling and softening site can be seen under the microscope. The lesions involve the gray matter and white matter of the spinal cord. The necrotic tissue is focal or fused into a sheet, and small cysts are formed. Axonal and nerve cells are lost. Neutrophils Infiltration, capillary proliferation, visible cuff-like infiltration of perivascular lymphocytes; other parts of the spinal cord can be seen scattered or fused into a piece of demyelinating changes. Cavity formation was observed in the contracted part of the spinal cord, the interstitial hyperplasia, and the Wallerian degeneration of the ascending and descending nerve fiber bundles.

     

    Optic nerve pathology

    Optic nerve inflammation includes lymphocytes, macrophages, monocyte infiltration, and vascular inflammation. After a long time, necrosis and cavity formation, vascular endothelial cell proliferation, glial cell proliferation or loss, optic nerve and optic detachment demyelination can be seen. Retrograde axonal injury results in loss of retinal nerve fiber layers.

    other

    In other parts of the NMO patients, other parts of the central nervous system, such as the brain stem, periventricular, and semi-oval center white matter, may present with a classic MS-like demyelinating lesion.

     

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