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NeuroMyelitis Optica (Devic's disease)

Please look up Dr Kevin Tan lecture"Neuroimmunology" in the ONE-E-Archive

The syndrome of neuromyelitis optica (NMO) is defined as the co-occurrence of optic neuritis with myelitis. This combination of neurological impairments occurs in patients with multiple sclerosis (MS), acute disseminated encephalomyelitis (ADEM), systemic lupus erythematosus (SLE), and Sjögren syndrome. NMO has been associated with several systemic diseases including collagen vascular diseases, autoantibody syndromes, infections, and toxic exposures.

The clinical course of NMO is variable. It may occur as a monophasic illness that is either fulminant and fatal or associated with varying degrees of recovery. Polyphasic courses characterized by relapses and remissions also occur (like in the chinese lady we examined during Prof Umapathi's ward rounds).

There is much debate as to whether NMO is a distinct disease, and what its relationship is to MS and other inflammatory disorders. Whether or not the NMO phenotype corresponds to a unique biologic process will await the identification of a disease-specific marker and, ultimately, the elucidation of the syndrome's pathogenesis.

Epidemiology

Rare, constituting less than 1% of demyelinating disease in Western countries.

Men and women thought to be equally affected, although in more recent case series women are overrepresented.

Age: Ranges from childhood to late adulthood, with the incidence apparently tapering off after the fifth decade.

Pathogenesis

NMO is similar to MS in that it is an autoimmune demyelinating disease. Unlike MS, the attacks are believed to be mediated by NMO-IgG antibodies.which target a protein called aquaporin 4 in the cell membrane of astrocytes which acts as a channel for the transport of water across the cell membrane. Aquaporin 4 is found in the processes of the astrocytes that surround the blood-brain barrier, which is weakened in NMO, but it is currently unknown how the NMO-IgG immune response leads to demyelination.

Clinical Features

Cases can present with either visual loss or myelopathy. Occasionally, optic nerve and spinal cord symptoms begin simultaneously. Either one or both eyes may be involved, and the extent of myelitis is variable.

May be preceded by a prodrome of fever, myalgia, headache, or sore throat.

Generally, NMO is sporadic, although there are a few case reports of familial occurrences.

Some patients have a monophasic illness, especially in the pediatric population. Others have polyphasic illness characterized by relapses and remissions with variable degrees of recovery between episodes. The proportion of patients in each of these two groups varies depending on the criteria used to define NMO.

In the pediatric population, NMO is frequently preceded by infection. Pediatric cases typically have a monophasic course and many have complete neurological recovery.

Physical Examination

Ophthalmoscopic examination may be normal or find signs of optic neuritis, or optic atrophy in chronic cases.

Visual field testing typically reveals a central scotoma.

Relative afferent pupillary dilation may be present, but can also be absent if both the optic nerves are affected equally.

The spinal cord symptoms in NMO are not different from those of other causes of myelitis.

Patients may suffer from painful tonic spasms.

Cerebral and brainstem findings should not be present; if they are present, a search for alternative etiologies is warranted.

Diagnostic Criteria

Mandler and colleagues (University of New Mexico)
#Clinical: Acute involvement of spinal cord and optic nerves, either coincidental or separated by months or years, independent of its subsequent progression but without the development of brainstem, cerebellar, or cortical features at any time in the disease course
  1. Imaging: Normal-appearing brain MRI; enlargement and cavitation on spinal cord MRI
  2. CSF: Decreased serum/CSF albumin ratio with normal CNS daily IgG synthesis and usually absence of oligoclonal bands
  3. Pathology: Spinal cord necrosis and cavitation with thickened vessel walls and absence of inflammatory infiltrates; demyelination of optic nerves with or without cavitation; no demyelinating lesions in the brain, brainstem, or cerebellum
Wingerchuk and colleagues (Mayo Clinic)
Diagnosis requires all absolute criterion and one major supportive criteria or two minor supportive criteria
Absolute criteria:
#Optic neuritis
  1. Acute myelitis
  2. No evidence of clinical disease outside of the optic nerve or spinal cord
Major supportive criteria:
#Negative brain MRI at onset (does not meet criteria for multiple sclerosis)
  1. Spinal cord MRI with signal abnormality extending over ≥3 vertebral segments
  2. CSF pleocytosis of >50 WBC/mm3 or >5 PMNs/mm3
Minor supportive criteria:
#Bilateral optic neuritis
  1. Severe optic neuritis with fixed visual acuity worse than 20/200 in at least one eye
  2. Severe, fixed, attack-related weakness (MRC ≤2) in one or more limbs
Differential diagnosis
Collagen vascular diseases and autoantibody syndromes
Systemic lupus erythematosus
Sjögren syndrome
p-ANCA autoantibodies
Anticardiolipin autoantibodies
Mixed connective tissue disease
Viral and mycobacterial infections
Varicella-zoster virus
Epstein-Barr virus
HIV
Tuberculosis
Toxic exposures
Clioquinol
Antitubercular medication
Idiopathic central nervous system demyelinating diseases
Asian-type multiple sclerosis
Western-type multiple sclerosis
Acute disseminated encephalomyelitis

Neuromyelitis optica

Diagnostic evaluation
Complete history, physical, and neurological examination
Basic laboratory studies

Autoimmune/Infectious disease workup

MRI

Spine, brain, and optic nerves The spinal cord MRI is typically abnormal with areas of increased signal intensity spanning several sections of the spinal cord on T2-weighted images and with gadolinium enhancement. The optic nerves can also be enhanced with gadolinium on TI-weighted images. By contrast, the brain MRI is often normal or may show nonspecific changes.

CSF analysis
Cell counts, total protein, glucose, IgG index, IgG synthetic rate, oligoclonal bands, VDRL, (PCR for herpes zoster virus), bacterial and mycobacterial stains and cultures

The CSF is often abnormal with mildly elevated protein and the presence of pleocytosis including polymorphonucleocytes.


Differences from Multiple Sclerosis

In well established cases of NMO, it is usually possible to accurately differentiate from MS. However, early in their course, it may be difficult to definitively separate these two conditions. However, there are some differences.

  • NMO affects only the optic nerves and spinal cord, whereas MS affects the brain as well.
  • Attacks of NMO tend to be more frequent and severe than in MS, though this is not always the case.
  • An MRI of the brain is typically normal in NMO, although this is not always the case; in MS the MRI of the brain typically shows many areas of inflammation.
  • An MRI of the spinal cord shows large extensive areas of inflammation of the spinal cord whereas in MS typically the areas are much smaller.
  • Spinal fluid studies tend not to show the typical elevation of antibodies detected in patients with MS.


Treatment

Unfortunately, there are no proven effective therapies for NMO. Steroids are typically used to treat cases acutely.

Plasma exchange may be tried in patients who do not respond to steroids.

Interferons and sometimes immunosuppressant drugs are used with the hope that further relapses will be prevented, but prospective data in support of their efficacy are lacking.

Source

Medscape review article

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