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This is a different pathology from multiple sclerosis (MS) and the primary target is astrocytes and not myelin sheaths

About

• Relapsing CNS demyelinating disease with different features to MS
• Neuromyelitis optica (NMO) is an autoimmune, inflammatory and demyelinating disorder of the CNS
• Has a predilection for the optic nerves and spinal cord.
• Commonest in young females

Aetiology

• The autoantibodies affect the astrocytes in the central nervous system, the disease is an astrocytopathy.
• Associations with Sjorgren's syndrome and SLE

Features

• An often severe myelopathy with MRI evidence of longitudinally extensive spinal cord lesion
• Optic neuritis is bilateral and severe or associated with a swollen optic nerve or chiasm lesion or an altitudinal scotoma
• Intractable hiccough or nausea/vomiting is present for >2 days with evidence of a periaqueductal medullary lesion on MRI.

Clinical

• UMN weakness below the lesion
• Sensory level below the lesion depending on extent of lesion
• Autonomic features - BP
• UMN sphincter weakness
• Visual loss and afferent pupillary defect may be bilateral
• Intractable nausea and vomiting
• Positive Rhomberg's sign
• Lhermittes phenomenom

Affected areas

• Optic nerve
• Spinal cord
• Area postrema of the dorsal medulla
• Brainstem
• Diencephalon
• Periependymal
• Corpus callosum
• Internal capsule
• Subcortical white matter).

Investigations

• U&E: hyponatremia due to SAIDH maybe seen
• Serum aquaporin-4 (AQP4) autoantibodies. Seropositive patients have a relapsing disease course.
• anti-MOG, has been detected in 20%
• MRI spinal cord lesions longer > 3 spinal segments and primarily involving the central part of the spinal cord on axial sections. There may be enhancement with contrast and some restricted diffusion. Brain often normal
• Visually evoked potential study (VEP study) may suggest optic neuropathy.
• CSF: absence of oligoclonal IgG bands

Comparing MS and NMO

• NMO is monophasic and not relapsing remitting
• NMO attacks are usually more severe with lasting disability.
• NMO more likely to get respiratory failure form cervical disease
• NMO MRI head can be normal
• NMO the MRI cord lesions are longitudinal and central
• NMO CSF oligoclonal bands absent
• NMO and MS are different diseases and require different treatments.
• NMO have a detectable antibody that targets Aquaporin-4 (AQP4)
• MS treatments (including interferon-ß) can exacerbate NMO

Wingerchuk classification criteria

• REQUIRED CRITERIA:
  • Optic Neuritis
  • Acute transverse myelitis
• SUPPORTIVE CRITERIA: (two of the three)
  • Longitudinal extensive cord involvement of more than three consecutive vertebral segments
  • MRI Brain not meeting the criteria for MS
  • Aquaporin 4 seropositivity

Management

• Immunosuppression. Acute aggressive management is of prime importance, as disability accrues with attacks. Even permanent and severe disability can occur after the very first episode. Management of relapses is with early corticosteroid treatment, typically 1g of intravenous methylprednisolone for 5 days followed by oral prednisone (1 mg per kg body weight) for a month, and then a gradual tapering off over a 6–12-month period.
• Alternative options include plasma exchanges (PLEX). Typically, 5-7 exchanges over a 2-week period. Early initiation of treatment (in addition to corticosteroids) is now considered standard practice. However, there is a lack of clinical trials and difficult ethical issues in running any form of placebo-controlled trials.
• Interferon-ß is now contraindicated in NMO. Many reports confirm not only its inefficacy but the tendency to cause severe relapses
• Azathioprine has been used with some success as the principal drug in relapse prevention. Its popularity was based initially only on a short case series, but recent larger retrospective case series vindicate its use
• Rituximab (RTX) as an anti-CD20 monoclonal antibody has gained popularity in the treatment of many immunological diseases and may be considered.
• Ongoing rehabilitation and support with residual neurology is important to get as much return of function.
• Pain, stiffness, fatigue, bladder and bowel symptoms, have to be managed with appropriate medications. The patient has tonic spasms: Carbamazepine often leads to rapid and gratifying relief.

References

• Current concept of neuromyelitis optica (NMO) and NMO spectrum disorders