Neuromyelitis Optica (NMO)

What is neuromyelitis optica?

In NMO, antibodies target aquaporin-4 (AQP4), a water channel found on astrocytes, the support cells of the brain and spinal cord. The attack triggers inflammation that damages the nerve fibers' insulation (myelin) and the nerves themselves. Areas rich in AQP4, the optic nerves, spinal cord and a brainstem region called the area postrema, are hit hardest.

NMO used to be considered a severe form of multiple sclerosis. The discovery of AQP4 antibodies in 2004 showed it is a separate disease, and the term NMO spectrum disorder (NMOSD) now covers all its forms.

A related but distinct condition, MOG antibody-associated disease (MOGAD), causes similar attacks and is tested for at the same time.

Symptoms of neuromyelitis optica

NMOSD usually comes in attacks (relapses) that build over days, separated by months or years. Recovery from each attack is often incomplete, so disability accumulates.

Optic neuritis

• Eye pain, often worse when moving the eye
• Blurred, dim or washed-out vision, loss of color vision
• Sometimes severe loss, down to seeing only light, in one or both eyes

Compared with typical optic neuritis in MS, NMO attacks are more often severe, involve both eyes, and recover less well.

Transverse myelitis

Transverse myelitis is inflammation across the spinal cord. In NMO it usually stretches over three or more vertebral segments. Symptoms include:

• Weakness or paralysis of the legs, sometimes the arms
• Numbness, tingling or a band-like feeling around the trunk
• Painful muscle spasms
• Loss of bladder and bowel control

Area postrema and brainstem attacks

• Persistent hiccups, nausea and vomiting lasting days without a stomach cause. This is a hallmark of NMO
• Double vision, dizziness, facial numbness
• Rarely, sleepiness or hormone changes from involvement of the hypothalamus

Who gets NMO and why

• Rare, affecting a few people in every 100,000
• Much more common in women
• Average onset around 40, but it can start in childhood or old age
• More common in people of Asian, African and Hispanic ancestry than in people of European descent
• Often occurs with other autoimmune diseases, such as lupus, Sjögren's syndrome and myasthenia gravis

It is not directly inherited, although rare families exist. Triggers for the first attack are unknown; infections sometimes precede attacks.

NMO vs multiple sclerosis

Getting the diagnosis right matters because several common MS treatments can trigger NMO relapses.

How NMO is diagnosed

1. AQP4-IgG blood test: a cell-based assay is the most accurate. A positive result plus one core clinical event confirms NMOSD.
2. MOG-IgG blood test: to identify MOGAD.
3. MRI of the brain, optic nerves and whole spine, looking for long spinal cord lesions and typical brainstem changes.
4. Lumbar puncture: spinal fluid in NMO often shows more white cells than in MS and usually lacks the oligoclonal bands typical of MS.
5. Eye tests: visual acuity, visual fields and optical coherence tomography (OCT) to measure nerve fiber loss.
6. Tests for related conditions, such as lupus and Sjögren's antibodies.

People without AQP4 antibodies can still be diagnosed using stricter clinical and MRI criteria.

Treatment

Treating an attack

Attacks are emergencies because the damage can be permanent.

• High-dose intravenous steroids for 3 to 5 days
• Plasma exchange (plasmapheresis), which removes antibodies from the blood. It is used when steroids are not enough, and increasingly given early in severe attacks
• Rehabilitation afterward: physical, occupational and vision therapy

Preventing relapses

Long-term treatment is recommended after diagnosis because most people with AQP4-positive NMO relapse without it. Options include:

• FDA-approved targeted drugs for AQP4-positive NMOSD: eculizumab and ravulizumab (complement inhibitors), inebilizumab (targets B cells) and satralizumab (blocks IL-6)
• Rituximab, a B-cell therapy used widely off-label
• Older oral immunosuppressants: azathioprine or mycophenolate, sometimes with low-dose steroids

Complement inhibitors raise the risk of meningococcal infection, so meningococcal vaccines are required before starting.

Managing symptoms

Muscle spasms, nerve pain, bladder problems, fatigue and depression are treated directly. A urologist can help with neurogenic bladder.

Outlook

Before modern treatment, many people developed severe vision loss or paralysis within a few years. With early diagnosis, fast attack treatment and preventive therapy, relapses are far less frequent and most people keep their independence. Outcome depends mainly on how many attacks occur and how well each recovers.

Frequently asked questions

What are the first symptoms of neuromyelitis optica?

The first symptoms are usually sudden vision loss with eye pain, or weakness, numbness and bladder problems from spinal cord inflammation. Some people first have days of uncontrollable hiccups, nausea and vomiting. Symptoms develop over hours to days and need urgent assessment.

Is neuromyelitis optica the same as MS?

No. Both attack the central nervous system, but NMO is driven by antibodies to aquaporin-4 or MOG, causes more severe optic nerve and long spinal cord attacks, and is treated differently. Some MS drugs can make NMO worse, so the distinction matters.

Is neuromyelitis optica curable?

There is no cure yet, but treatment controls it well. Newer targeted medicines prevent most relapses in many people with AQP4-positive NMOSD. Attacks are treated quickly with steroids and plasma exchange to limit lasting damage.

What is the life expectancy with NMO?

With modern treatment, most people with NMO live for many decades. Life expectancy has improved markedly as preventive medicines reduce severe attacks. The main risks come from severe spinal cord or brainstem attacks affecting breathing, and from infections, which is why relapse prevention is so important.

Is NMO hereditary?

Rarely. Most people with NMO have no affected relatives. A few families have more than one case, and certain immune genes slightly raise risk, but the disease is not directly passed from parent to child in most cases.