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At first glance, neuromyelitis optica (NMO) can look a lot like multiple sclerosis (MS). For years, doctors even believed that NMO was a rare form of MS. Now researchers know that NMO — also known as neuromyelitis optica spectrum disorder (NMOSD) or Devic disease — is a separate condition that requires specific tests to diagnose correctly.
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Because NMO and MS share some features and can be hard to tell apart, getting the right diagnosis can be tricky. Some people are told they have MS and years later learn they actually have NMO.
In this article, we’ll discuss how NMO is diagnosed, including key blood tests, imaging scans, and other tools that doctors use to find clear answers.
Because NMO shares many symptoms with MS, which is more common, not everyone gets the correct diagnosis right away. Both conditions are autoimmune diseases that damage or destroy myelin (the protective coating around nerves and brain cells in the central nervous system) — although they target different substances. This demyelination can cause vision loss, numbness, and weakness — symptoms common in both conditions.
NMO often affects the optic nerves, spinal cord, or brainstem. These attacks can be more severe or last longer than — but occasionally look similar to — MS.
Due to these similarities, doctors rely mainly on special blood tests, imaging, and other tools to make an accurate diagnosis and recommend the best treatment plan.
The first step toward a diagnosis involves a careful review of your medical history and symptoms. A neurologist will ask when your symptoms began, how long they lasted, and how well you recovered after each attack. They’ll also perform a full neurological exam to check your coordination and muscle strength, as well as your thinking, memory, vision, and speech.
You may also need to see an ophthalmologist (a doctor specializing in eye diseases) to check for optic neuritis (inflammation of the optic nerve). This inflammation can cause eye pain and sudden vision loss.
Your doctor will also look for patterns that may suggest transverse myelitis — inflammation in the spinal cord that can cause weakness, numbness, or paralysis in the arms or legs, plus bladder and bowel symptoms.
Some people also have long bouts of hiccups, nausea, or vomiting. This is called area postrema syndrome and may reflect brainstem involvement.
After the exam, your doctor will likely order blood tests for specific antibodies if they suspect NMO. Antibodies are proteins made by the immune system that can mistakenly attack healthy cells. In NMO, certain antibodies are key markers that help doctors confirm the diagnosis.
The main blood test for NMO looks for a type of antibody called aquaporin-4 immunoglobulin G (AQP4-IgG). These are autoantibodies — they attack your own tissues instead of germs that cause illness. In NMO, AQP4-IgG targets a water channel protein called aquaporin-4. In the central nervous system, these proteins are found on cells in the brain, spinal cord, and optic nerves.
A positive AQP4-IgG test is one of the strongest markers of NMOSD. In one 2025 study of 94 people with NMOSD, researchers found that 82 percent had these antibodies.
A few methods can be used to detect the antibodies, but research has shown the importance of using a cell-based assay. This test mixes a blood sample with specially prepared cells that carry the aquaporin-4 protein. Other methods, such as the enzyme-linked immunosorbent assay (ELISA), may produce unreliable results.
In people who have symptoms similar to NMO but don’t test positive for anti-AQP4 antibodies, researchers recently identified a different antibody. This discovery led to the description of a separate condition called myelin oligodendrocyte glycoprotein (MOG)-associated disease, which has its own clinical features.
The most common test for diagnosing NMO is magnetic resonance imaging (MRI). MRI scans help doctors see where inflammation or damage has occurred in the central nervous system.
MRI uses strong magnets and radio waves to produce detailed pictures of the brain and spinal cord. The procedure is painless. You’ll lie on a table that slides into a large, tunnel-shaped scanning chamber. The scan may take 30 minutes to an hour.
Doctors look for areas of damage, called lesions. In NMO, spinal cord lesions are often longer and more severe than those seen in multiple sclerosis. In MS, brain lesions are usually smaller and appear in different patterns.
A lumbar puncture — also called a spinal tap — helps doctors learn more about what’s happening in the nervous system. This test checks cerebrospinal fluid (CSF), the clear liquid that surrounds and protects the brain and spinal cord.
You’ll likely sit up or lie on your side for the procedure, which may take about 45 minutes. The doctor will insert a needle between two bones in your spine to collect a small amount of fluid. This sample is sent to a lab for testing.
The lab looks for signs of inflammation and certain immune system markers, such as oligoclonal bands. These bands are common in MS but usually absent in NMO. Sometimes, the CSF in people with NMO also shows higher white blood cell counts during an attack. This result may also help distinguish NMO from MS.
Evoked potentials measure how quickly nerves send signals to the brain. These stimuli response tests can help doctors find nerve damage that might not show up on an MRI.
For this test, small electrodes are placed on your scalp and sometimes your arms or legs. You may watch flashing lights, listen to sounds, or feel light taps during this painless test, which takes about an hour.
Optical coherence tomography (OCT) is a painless eye scan that uses light waves to take detailed pictures of the retina (the part of your eye that helps you see).
In NMO, OCT often shows thinning of retinal nerve fibers, which indicates nerve damage from optic neuritis. Some people may also have small areas of swelling or changes in tiny blood vessels in the retina.
Although OCT can help doctors measure and track eye damage, it can’t be used alone to diagnose NMO.
To make a diagnosis of NMO, doctors look for these six core clinical features:
If a person is seropositive — meaning they test positive for AQP4-IgG antibodies — diagnosis requires just one core feature. Someone who is seronegative (no AQP4 antibodies found) must have specific MRI features and at least two core features, which must include area postrema syndrome, optic neuritis, or myelitis.
If you’re not sure what your test results mean, talk with your neurologist. They can explain the results of each test and help you understand your treatment options.
It’s important to know that while a positive AQP4 antibody test confirms NMOSD, a negative result doesn’t rule it out completely. Other findings, such as MRI scans, spinal fluid results, and your clinical history, are reviewed together to make a final diagnosis.
Getting an early and accurate diagnosis of NMO matters because each attack can cause lasting nerve damage. The sooner NMO is found, the sooner treatment can begin to help prevent new relapses and protect your vision and movement. Starting the right therapy early can lower your risk of long-term disability and help you maintain a better quality of life.
On MyMSTeam, people share their experiences with multiple sclerosis, get advice, and find support from others who understand.
What tests led to your diagnosis of MS or NMOSD? Let others know in the comments below.
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