Using an MRI to Diagnose NMO

Reviewed by: HU Medical Review Board | Last reviewed: September 2021

Magnetic resonance imaging (MRI) is a common tool for diagnosing neuromyelitis optica spectrum disorder (NMO). Most people with NMO will have abnormal MRI results. Your doctor will order MRIs of the brain, orbits (eye area), and spinal cord to look for signs of NMO.1,2

How does an MRI work?

MRI machines use a powerful magnet and radio waves to take an image of the inside of the body. MRI does not use any radiation. This makes it a helpful imaging tool for people who should not be exposed to radiation, like children or people who are pregnant.1

The magnet affects the hydrogen atoms that exist within the water molecules of our body. Different types of tissues have varying levels of water content. This is how the images created by the magnet highlight different structures. Fluid shows up differently than air, muscle shows up differently than bone, and so on.1

The images created by MRI are very clear. They show much more detail than an X-ray or computed tomography (CT) scan. This is why MRIs are used to diagnose NMO and track its progression.

MRIs also take longer to complete. X-rays and CT scans take seconds to finish. MRIs can take many minutes to an hour or longer depending on the part of the body imaged.

Radiologists are doctors trained to read images of the body. They look for any signs of inflammation, masses, or other issues.1

What can be seen on an MRI scan?

The most common signs of NMO in MRI scans are lesions in the brain, orbits (eye area), and spinal cord. These may look like small bright spots in the MRI image. 2

Lesions are areas of active inflammation where NMO is damaging the myelin (protective covering) of nerves. The brighter the spot, the more recent the inflammation. In some cases, lesions with different levels of brightness can be seen. Less bright lesions have been present for a longer time. More recent lesions are also often larger than older ones because they are more inflamed.

Often, an MRI for NMO is done with contrast and without. Contrast is a substance given through the veins during the scan. Contrast helps show different kinds of tissues on the images. This can help your doctor distinguish between new and old lesions caused by NMO.

Spinal cord lesions

Most people with NMO have extensive lesions on their spinal cord, often spanning at least 3 vertebral segments. The spinal cord may appear swollen during an acute attack. Shorter lesions are less common. With treatment, spinal cord lesions get smaller.2,3

Six out of 10 people with NMO will have lesions and swelling in the cervical cord, which is located in the neck. These lesions may even extend from the neck into the bottom of the brain (medulla).2

Orbit lesions

The eye orbit includes the bony eye socket and the tissue and nerves that sit inside the socket. With NMO, the optic nerves may appear swollen on MRI. Lesions are often longer than in multiple sclerosis. Some studies suggest that more extensive lesions of the orbit may be one way to distinguish NMO from MS.2,3

Brain lesions

Five to 8 out of every 10 people have normal MRI images in the early stages of the disease. However, eventually, nearly all people with NMO develop lesions in the brain.2,3

Monitoring progression and treatment of NMO

Follow-up MRI scans can help keep track of your NMO. As the disease progresses, more lesions may develop.

The timing of repeat MRIs may vary between doctors. Many experts suggest getting scans in the same machine whenever possible to best compare images over time.

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