Neuro Disorders: Neuromyelitis Optica
Neuromyelitis Optica (NMO), also called as Devic’s disease is a neurological disorder that involves both optic nerves and the spinal cord.
Optic nerve is the nerve of vision and it is the (2nd cranial nerve, there are total 12 cranial nerves).
Neuromyelitis Optica is grouped under autoimmune, demyelinating and inflammatory type of diseases.
An autoimmune disorder because patient’s body immunity, a protective mechanism in the body, instead of protecting paradoxically attacks the body organs and tissues (in this case the optic nerve & spinal cord).
A demyelinating disease because the myelin tissue is what gets damaged in this disease. Myelin tissue is a complex of fat and protein that wraps up around the nerve fibers and helps in accelerating the conduction of nerve impulses along them.
An inflammatory disease because the damage takes place as a result of inflammatory process. Inflammation is a form of defense mechanism in the body that also helps in repair & healing process, however sometimes inflammation develops in the body without any need for it and this can be problematic like in NMO.
Is NMO a type of MS (multiple sclerosis)?
There has been a long confusion whether NMO is a type of MS or it is a different disease. The recent consensus is towards both being different diseases. NMO does present somewhat similar to MS with optic neuritis, myelitis etc however there are lot of differences too. The typical MS lesions in the brain are not seen with NMO. MS results due to cell mediated injury where as NMO results due to antibody mediated injury.
Although NMO too can present with recurrent attacks it is more typical nature of MS to present with recurrence.
Optic neuritis and spinal cord lesions are the main features of this disease. Generally one starts and the other one joins later. Optic neuritis presents as blurring of vision or loss of vision. Generally starts with one side and other side joins later but sometimes both sides are affected together.
Spinal cord lesions are larger compared to MS and involves typically about 2 or 3 segments. This will present as myelopathy and may present with various manifestations in different combinations of limb weakness, gait ataxia, bowel and/or bladder involvement, sensory loss or complaints etc.
There are certain criteria that are to be fulfilled to make a diagnosis of NMO. First of all there must be evidence for involvement of both the optic nerves and the spinal cord. Then out of the following 3 at least 2 criteria must be present;
1) The MRI of the brain findings should not resemble MS
2) If the spinal cord lesion is present then it must be larger than usual MS lesions (extend about 3 segments or more)
3) Blood test positive for auto-antibodies (IgG type). These antibodies target an antigen by name aquaporin 4 in the optic nerve and spinal cord and trigger the damage.
CSF analysis is routinely not required especially in typical cases since we do not expect to see the increased oligoclonal bands with NMO and the presence of this finding is more in favor of MS.
The treatment approach also differs from that of MS to some extent.
For the acute attack both MS and NMO are treated with intravenous solumedrol (methyl prednisone)however severe NMO cases that do not respond to IV steroids are supposed to be treated with plasmapheresis.
For the prevention of future attacks MS is typically treated with immunomodulator agents like interferon beta or glatiramer acetate at least in the beginning, where as NMO from the beginning requires immunosuppressive agents like azathioprine with or without oral steroid like prednisone.
A neurologist is frequently involved in the care of patients with Neuromyelitis Optica
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