Multiple sclerosis (MS) is a disease in which the body’s immune system attacks myelin, the outside layer of nerve cells.

Neuromyelitis optica (NMO) is also an immune system attack. However, in this condition, the attack is focused only on the central nervous system (CNS). It’s sometimes just called neuromyelitis or Devic’s disease.

NMO is a rare disease that damages the optic nerve, brain stem, and the spinal cord. The cause of NMO is an immune system attack on a protein in the CNS called aquaporin-4.

It leads to optic neuritis, which causes pain in the eyes and loss of vision. Other symptoms can include muscle weakness, numbness, and bladder control problems.

To diagnose NMO, doctors use MRI scans or check spinal fluid. NMO can be diagnosed with a blood test for the aquaporin-4 antibody.

In the past, doctors thought that NMO didn’t attack the brain. But as they learn more about NMO, they now believe that brain attacks can occur.

MS attacks the entire CNS. It can affect the optic nerve, spinal cord, and brain.

The symptoms include numbness, paralysis, vision loss, and other problems. Severity varies greatly from person to person.

A variety of tests are used to diagnose MS.

While there’s currently no cure, medications and treatments can help manage some symptoms. MS doesn’t usually affect life expectancy.

Because NMO is so similar to MS, scientists previously believed it might be a form of MS.

However, scientific consensus now distinguishes NMO from MS and groups it with related syndromes under the unifying term “neuromyelitis optica spectrum disorder (NMOSD).”

The Cleveland Clinic reports that NMO attacks do more harm than MS does to certain parts of the body. The clinic also points out that NMO doesn’t respond to some of the drugs that help relieve MS symptoms.

MS and neuromyelitis differ in the impact that episodes have on the body.

Symptoms of MS attacks are less severe than NMO attacks, especially in the early stages of the disease. The cumulative effects of these attacks can become very serious. However, they may also have a limited impact on a person’s ability to function.

NMO attacks, on the other hand, can be severe and lead to health problems that can’t be reversed. Early and aggressive treatment is important in reducing the harm caused by NMO.

The course of both diseases can be quite similar. Some people with MS experience remitting episodes, ones in which symptoms come and go. The more common form of NMO also occurs in attacks that return on a regular basis.

However, the two conditions can differ as well.

NMO may strike once and last for a month or two.

Some types of MS don’t have periods in which symptoms go into remission. In these cases, symptoms simply get progressively worse over time.

NMO doesn’t have a progressive course like MS can. The symptoms in NMO are due only to attacks.

MS is much more common than NMO. Nearly 1 million people in the United States have MS, according to the National Multiple Sclerosis Society. People with MS tend to be concentrated in areas farther from the equator.

NMO can be found in any climate. According to the National Multiple Sclerosis Society, there are about 250,000 cases around the world, including around 4,000 in the United States.

Both MS and NMO are more common in women than in men.

Both MS and NMO are incurable. There’s also no way to predict who’ll develop either of the diseases. However, medications can help treat symptoms.

Because NMO is likely to return after the first episode, people are usually prescribed drugs to suppress the body’s immune system. Randomized clinical trials are beginning to assess the efficacy and safety of a variety of immunotherapies in treating NMO.

New MS medications are meant to reduce symptom flare-ups and treat the underlying causes of the disease.

Attacks of NMO and MS may be treated with corticosteroids and plasma exchange.

If you suspect you might have either of these nerve conditions, see your doctor for a proper diagnosis. The sooner you’re diagnosed, the sooner you can start treatment to address any symptoms and potential complications.

Both conditions are incurable, but neither condition is fatal. With proper care, you can have a healthy and an active life.