What Is Neuromyelitis Optica (NMO)?

Reviewed by: HU Medical Review Board

Neuromyelitis optica (NMO) is an autoimmune condition. NMO refers to inflammation in nerves that connect the retina of the eye with the brain (optic nerve; “optica”) and inflammation in the nerves of the spinal cord (“myelitis”).1,2

NMO is also called Devic disease. Due to improved diagnostic testing, the term neuromyelitis optica spectrum disorder (NMOSD) is now recommended as not everyone with this disease develops inflammation of the optic nerve and spinal cord, at least initially. NMO is encompassed under the term NMOSD.1,2

NMOSD typically causes episodes of symptoms that worsen over a few days. Common symptoms include vision loss and limb weakness. These are also common symptoms of multiple sclerosis (MS). Doctors must use blood tests and other exams to distinguish NMOSD from MS. Treatment then involves reducing symptoms during episodes, preventing future episodes, and rehabilitation.1,2

What causes NMOSD?

NMOSD is an autoimmune condition. This means that your immune system mistakenly attacks healthy cells instead of germs. In NMOSD this happens due to antibodies that target specific cells.3

Many people with NMOSD have antibodies that target aquaporin-4 (AQP4). This is a protein found on brain cells called astrocytes. AQP4 antibodies are also called AQP4-IgG. People with AQP4-GgG in their blood are often referred to as being “AQP4-positive.”1,4

AQP4 helps control the water balance in the brain. Attacking astrocytes with APQ4 antibodies triggers inflammation that damages nerves and the protective coating around them. This causes injury to the optic nerve and spinal cord.1,4

Another autoimmune condition that causes inflammation in the optic nerves and spinal cord is myelin oligodendrocyte glycoprotein (MOG) antibody disease (MOGAD). People with MOGAD have antibodies that target MOG.5

MOG is a protein on the protective covering of nerves. Attacking cells that express MOG leads to the inflammation of the optic nerve and spinal cord.5

In the past, NMO was thought to associate with antibodies to both AQP4 and MOG. However, research has now shown that these antibodies identify distinct diseases. While initial clinical presentations can be similar, treatment responses to various therapies are different in NMOSD and MOGAD.4,5

We do not know what causes these autoimmune reactions in people with NMOSD or MOGAD. Sometimes, NMOSD can happen after a respiratory infection.2

What are the symptoms of NMOSD?

A main feature of NMOSD is inflammation of the optic nerve (optic neuritis). This can lead to:4

  • Some degree of vision loss, sometimes in 1 eye (but often both)
  • Eye pain that worsens with eye movement

Another common feature of NMOSD is inflammation of the spinal cord (transverse myelitis). This can lead to:4

  • Limb weakness or paralysis
  • Bladder and bowel dysfunction
  • Sensory loss below a certain level in the body
  • Painful spasms

NMOSD can also involve systems other than the optic nerve and spinal cord. Other symptoms include:4

  • Nausea, vomiting, and hiccups
  • Excessive daytime sleepiness (narcolepsy)
  • Posterior reversible encephalopathy syndrome (PRES)
  • Seizures in children

More than 90 percent of people with NMOSD have discrete episodes or “attacks” of symptoms. This is called relapsing NMOSD. Attacks usually occur over days, with recovery time over weeks to months. People with NMOSD often do not recover fully from attacks. For example, they may be left with some long-term vision loss. Over time, recurring attacks lead to accumulating disability.4

Historically, about 5 percent of people with NMO have symptoms only once. This is called monophasic NMO.4

Who gets NMOSD?

NMOSD affects 1 to 10 out of 100,000 people worldwide. Many people with NMOSD are misdiagnosed with MS. So this number may actually be higher.2,6

People of any age can have NMOSD. The average age that NMOSD symptoms begin is between 32 and 40. Women are 3 to 5 times more likely to have NMOSD compared to men. It is also more common among people of Asian or African descent.4,7

How is NMOSD diagnosed?

NMOSD can be hard initially to distinguish from MS. Both conditions cause optic neuritis and myelitis. Slight differences in symptoms can lead doctors to favor NMO or MS. Your doctor must use certain tests to diagnose NMOSD. These can help distinguish NMO from MS. Tests include:3,4

  • Neurological exam of muscle strength and coordination
  • Blood tests for antibodies to AQP4 and MOG
  • MRI of the brain, optic nerves, and spinal cord
  • Spinal tap to analyze your spinal fluid

How is NMOSD treated?

There is not yet a cure for NMOSD. Treatments can significantly improve the long-term outcomes of NMOSD. Treatment is focused on:1,3,8

  • Reducing symptoms during an attack
  • Preventing future episodes (relapses)

The standard treatment to reduce symptoms during an attack is steroids. These are usually given through a vein in the arm initially. If steroids do not help, another option is plasma exchange. This process can cleanse your blood by removing harmful substances including antibodies to AQP4.3,8

Many treatment options can reduce relapses. The right treatment for you depends on personal factors, including whether you have AQP4 antibodies. All NMOSD treatments suppress the immune system. Common treatments to prevent NMOSD attacks include:1,3,8

  • Biologics or lab-created antibodies that suppress the immune system
  • Chemical drugs that suppress the immune system

In many cases of NMSOD life-long treatment is needed.8

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