Neuromyelitis optica spectrum disorder (NMO/NMOSD)

What neuromyelitis optica is

Neuromyelitis optica is an autoimmune disease of the central nervous system. The immune system makes antibodies that attack healthy tissue in the optic nerves and spinal cord. Some parts of the brain can be hit too.

In most people, the target is a protein called aquaporin-4. It sits on astrocytes, the cells that support and protect nerves. When the antibody binds to it, it sets off a group of immune proteins called complement. That causes swelling and damage. Myelin, the coating on nerve fibers, can be harmed along the way.

That's a different process from MS, where the attack centers on myelin itself. NMO was once thought to be a type of MS. Experts now see them as distinct diseases.

In 2015, an international panel created the term NMOSD. It brought together classic NMO and related patterns into one spectrum. The panel split it into two groups: NMOSD with AQP4 antibodies, and NMOSD without them. Another illness, MOGAD, can look similar but is now classed on its own.

Sources: NINDS: NMOSD; MedlinePlus Genetics: neuromyelitis optica; Neurology: NMOSD consensus criteria; Guthy-Jackson Foundation: NMO FAQs; J Neurol: MOGAD review.

NMOSD symptoms

NMOSD symptoms depend on where an attack happens. Each attack can damage new areas, so problems can add up over time.

The third row surprises many people. A small brainstem area called the area postrema can be involved. An attack there can cause vomiting or hiccups that go on and on. Of course, hiccups and vomiting have many common causes. On their own, they don't point to this rare disease.

Spinal cord attacks can also cause shooting pain or tingling in the neck, back, or belly. Muscle weakness from a severe attack can also make breathing hard. That can become life-threatening.

Sudden loss of sight, new weakness, loss of bladder control, or trouble breathing needs urgent care. Don't wait to work out which disease name fits.

Sources: NINDS: NMOSD; MedlinePlus Genetics: neuromyelitis optica; Guthy-Jackson Foundation: NMO FAQs; Neurology: NMOSD consensus criteria.

What causes neuromyelitis optica

The exact cause of NMO is unknown. Most experts think it comes from a breakdown in immune tolerance. That is the immune system's ability to tell the body's own cells from outside threats.

NMO doesn't usually run in families. No gene has been tied to it, though a small number of people have an affected relative. Many genetic and environmental factors likely play a part.

Some groups are more likely to get it:

• Women, especially in the relapsing form, where about 9 women are affected for every man
• Black Americans, and people with African, Asian, or Caribbean ancestry
• People with other autoimmune diseases

About a quarter of people with NMO have signs of another autoimmune disease. These include myasthenia gravis, lupus, and Sjogren's disease. Our page on MS vs lupus explains how lupus differs from MS.

It's also unclear what sets off each attack. Antibody levels rise during attacks and fall between them with treatment. But what starts or ends an attack is still unknown.

Sources: Guthy-Jackson Foundation: NMO FAQs; MedlinePlus Genetics: neuromyelitis optica; NINDS: NMOSD.

How NMOSD is diagnosed

Doctors combine the type of attack, MRI scans, and blood tests, while checking for other causes. The key blood test looks for AQP4 antibodies, sometimes called the NMO-IgG test. A primary care doctor or neurologist can order it.

The test is strong evidence, but it isn't perfect. The Guthy-Jackson Foundation's FAQ says most versions list a 5 to 10 percent chance of a false positive and a 20 to 30 percent chance of a false negative. How accurate a result is depends on the test method: the 2015 international criteria favor cell-based tests, so ask which method your lab used.

MRI helps too. In a spinal cord attack, the inflamed area often stretches along 3 or more bones of the spine. That long lesion is a strong clue. Eye tests, such as optical coherence tomography, can show damage to the optic nerve or retina.

Here's how a test result changes the next step:

1. AQP4 positive, with a matching attack: this strongly supports NMOSD with AQP4 antibodies, once other causes are ruled out.
2. AQP4 negative: NMOSD is still possible, but the rules are stricter. They call for stronger clinical evidence plus certain MRI findings.
3. AQP4 negative and the picture is unclear: doctors often test for MOG antibodies. Up to half of people with AQP4-negative NMOSD test positive for MOG.
4. Neither antibody, and the pattern fits MS better: the team may look at MS criteria instead.

Sources: Neurology: NMOSD consensus criteria; Guthy-Jackson Foundation: NMO FAQs; MedlinePlus Genetics: neuromyelitis optica; SRNA: MOGAD fact sheet.

NMO vs MS vs MOGAD

NMO is sometimes mistaken for MS. The two share symptoms, but they are different diseases with different treatments. Some medicines used for MS may not help NMO, or may even make it worse.

This table is a guide, not a scorecard. Early results don't always fit one column, and a diagnosis may change as new findings come in. Read more in our guides to MOGAD and how MS is diagnosed.

Sources: Guthy-Jackson Foundation: NMO FAQs; NINDS: multiple sclerosis; SRNA: MOGAD fact sheet; NINDS: NMOSD.

Neuromyelitis optica treatment and outlook

NMOSD can't be cured yet, but treatment can lower the chance of new attacks. Care has two parts: treating an attack, and preventing the next one.

For an attack, specialists may consider strong, fast-acting steroids. Plasma exchange, a procedure that filters harmful antibodies from the blood, may also be used. How long steroids continue after an attack is a specialist's decision.

To prevent attacks, specialists may consider long-term medicines that calm the immune system. Some have FDA approval specifically for NMOSD. Others are broader immune medicines used for this purpose. People often take these for a long time. In one large trial, 3 percent of people with AQP4-positive NMOSD on one of these medicines had a relapse, compared with 43 percent on placebo. That trial did not show a clear difference in disability over the same period. The specialist weighs the benefits and risks of each option with the patient.

Other care helps with what attacks leave behind. That includes treatment for pain, stiffness, spasms, and bladder or bowel problems. Physical and occupational therapy can help with walking, balance, and daily tasks.

Recovery between attacks is often partial, and problems can build up. That's why fast diagnosis and treatment of each attack matter. Our pages on optic neuritis and transverse myelitis go deeper on those two kinds of attack.

Sources: NINDS: NMOSD; MedlinePlus Genetics: neuromyelitis optica; Guthy-Jackson Foundation: NMO FAQs; NEJM: relapse prevention trial in AQP4-positive NMOSD.

Who this page is for

People who've just heard the words neuromyelitis optica, and those helping them through it, are who we had in mind. Anyone whose MS diagnosis is being rechecked may find it useful too. It describes the disease, but it isn't a treatment plan for one person. Bring your scans and test reports to every visit, and ask what each one means.