Neuromyelitis optica (NMO), also known as Devics disease or Devic's syndrome, is a rare type of autoimmune channelopathy associated with the antigen Aquaporin-4 water channel found in astrocytes which surround and protect the blood brain barrier in central nervous system (CNS). It causes inflammation and demyelination of the optic nerve and spinal cord.
The disease is related to the following processes: degenerative and has an incidence of about 1 / 100.000.
Neuromyelitis optica (NMO) is a rare autoimmune disease of the central nervous system (CNS) that presents classically with inflammation and demyelination of the optic nerve (optic neuritis) and spinal cord (transverse myelitis)  . It is characterized by loss of vision and disturbed spinal function.
Visual pathway symptoms (Optic neuritis)
Spinal cord dysfunction (Longitudinally extensive transverse myelitis (LETM))
Due to its striking similarity to multiple sclerosis (MS), NMO was considered to be a variant of multiple sclerosis and often was and is still misdiagnosed. The key features differing NMO from MS are as follows:
NMO is further divided into 2 main types:
Blood tests can detect anti-aquaporin-4 antibody (NMO-IgG). It is highly specific (>99%) but has a sensitivity of 48-72% depending on the assay used.
Treatment and prevention
For acute management of the disease, IV prednisolone and plasma exchange(PLEX) are considered. To prevent relapses-immusuppresants including mycophenolate mofetil or rituximab are considered along with rehabilitation.
It isn't well understood as to why aquaporin-4 in CNS is attacked. NMO is known to being an autoimmune disease but in patients with non-relapsing variant, antibodies to myelin oligodendrocyte glycoprotein were discovered by researchers in the UK and Japan which shows immunological heterogenecity.
Nearly 50% of the patients show strong family history of autoimmunity. Though 95% of the patients have no family history of NMO but 3% of them have reported family history of other neurological condition.
Though the incidence of NMO per 100,000 population ranges between 0.053 to 0.40, the prevalence per 100,000 population ranges 0.52 to 4.4 .
The most characteristic feature of NMO is the autoantibodies produced against aquaporin-4 (AQP4-Ab). The pathogenesis of NMO is based on in vivo and ex vivo experiments that were concluded as follows:
NMO AQP4-Ab possitive belong to a spectrum of autoimmune diseases of the CNS but with the recent discovery of AQP4-Ab autoimmunity; a new spectrum called the 'NMO spectrum disorder', 'aquaporinopathy' or 'autoimmune AQP4 channelopathy' was proposed. Despite of the recent advances, researchers havent been able to identify the pathogenesis behind AQP-4Ab seronegative patients thereby posing a challenge to treat such patients. Studies are also focusing on the T cell involvement in NMO patients. NMO was thought to be a subset of MS for a long time which is proven wrong now hence MS approved treatment modalities are condemned for NMO patients as they cause more harm than good.
According to prospective series and few retrospective studies, several treatment methods have proven effective in preventing an attack and stabilizing NMO patients while relapses were prevented by early intervention wtih immunosuppresants .
The prognosis for neuromyelitis optica is not very promising and involves various factors especially number of relapses in initial years of the disease. Complete recovery is unlikely due to frequent relapses. Patients with relapses tend to have slow prognosis ranging from weeks to months. Frequent and severe relapses lead to early disability .
Approximately more than 50% of the patients suffering from neuromyelitis optica end up blind in one or both the eyes in just a span of 5 years posing the necessity of ambulatory help. The overall prognosis significantly depends on the severity of the first attach, the number of relapses during the first 2 years of the course of disease and presence of other autoimmune disorders like systemic lupus erythematosus (SLE)  .
Symptoms of optic neuritis:
Symptoms of myelitis:
As mentioned earlier MS and NMO are often confused together. Though both present similarly but NMO presents more severely than MS. MRI findings are normal in NMO unlike in MS and spinal tap does not show oligoclonal bands in NMO as compared to MS. NMO patients usually show improvement in vision and paralysis with high dose of corticosteroids with a partial recovery of the sensory and motor functions. Repeated attacks cause permanent damage leading to blindness or impaired mobility.
Diagnosis of NMO can be done as follows:
Treatment modality revolves around corticosteroids and plasmapheresis.
Since MS and NMO were always considered to be one entity, it was believed that the immunomodulatory therapies of MS would help NMO patients. But recent studies have shown that they prove no benefit to the patient and are to be used only in cases of relapse .
Depending on the AQP4 antibody status, the prevention approach differs.
Postivie AQP4 antibody: Patients who are AQP4 antibody positive and fulfill the NMO criteria and have relapses would need immunosuppressive or immunomodulatory treatment to prevent further relapses.
Negative AQP4 antibody: Patients who have a negative AQP4 antibody and have had a single attack of LETM or ON don't need any preventive measure unless they have relapse. If relapse occurs, immunosuppression is the way to go to avoid further relapses.
Recurrent relapses increase the chances to keep a patient on immunosuppressive therapy risking long term side effects. Hence the goal in NMO is to achieve faster remission by tapering the dose of corticosteroids in a patient who responds well to them and help curb the side effects.
Neuromyelitis optica (NMO) is a demyelinating disorder that affects the eyes and spinal cord. The underlying etiology is still unknown but its cause is often believed to be due to an autoimmune condition or post infection.
NMO is considered to be an autoimmune disease and has been associated with an abnormality in channelopathy. The presence of an antibody against the Aquaporin-4 is believed to cause the symptoms seen in NMO.
The symptoms are related to both eyes and the spinal cord.
Symptoms related to eye:
Symptoms related to spinal cord:
Diagnosis revolves around imaging studies and blood tests.
Unfortunately till date no treatment exists. Various attempts are made to slow the progression of the disease and prevent relapses.