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What to Know About Lesions and MS

Reviewed by: HU Medical Review Board | Last reviewed: August 2023

Multiple sclerosis (MS) is an autoimmune disease. For people with MS, the immune system mistakenly attacks the protective covering on nerve fibers. This covering is called myelin.1

The attacks by the immune system lead to the formation of lesions in the central nervous system (CNS). Lesions are areas of damage or inflammation.1

What are lesions?

The myelin sheath is a layer around the nerves. It allows for efficient transmission of signals between the brain, spinal cord, and the rest of the body. When the myelin is damaged, the nerve signals become disrupted and neurons can degenerate. This can lead to various MS symptoms.1,2

A lesion is a damaged or scarred area. In MS, they are caused by the inflammation from the immune system attacking the myelin. Lesions are sometimes called plaques. Not all lesions in the CNS are caused by MS. But lesions are an important sign of MS. Doctors use the presence and location of lesions to help diagnose and track MS.1,2

MS lesions can occur throughout the CNS, including the brain, spinal cord, and optic nerves (the nerves that transmit signals from the eyes). Lesions are caused by focal inflammation that results in damage to the myelin and nerves. This damage ultimately leads to scar tissue. Lesions can vary in size and location. Lesions can be detected with imaging techniques such as magnetic resonance imaging (MRI).1,2

What do lesions look like on MRI scans?

Doctors use MRI scans to look for lesions. In MS they often use an MRI scan with contrast. This means they inject a contrast fluid that contains gadolinium. The gadolinium shows up white (“lights up”) on certain MRI sequences where inflammation is happening. So, doctors look for white patches on these MRI sequences to detect active lesions with inflammation. Lesions older than 3 months typically will not light up with gadolinium.2,3

While gadolinium only highlights newer lesions with ongoing inflammation, other MRI sequences can reveal all lesions, new or old, without any gadolinium. Combining these different MRI techniques allows doctors to identify both newer active and older inactive lesions.2,3

Over time, some lesions may show up as a black spot on some MRI sequences. This means the CNS tissue has suffered so much damage that it completely degenerates or disappears. Some lesions have been shown to grow slowly over time. These are called chronic active lesions or smoldering lesions. Research shows that smoldering lesions may be a risk factor for progressive MS.1,2

How are lesions used to diagnose and monitor MS?

Lesions play an important role in the diagnosis and monitoring of MS. Diagnosing MS often involves imaging, like an MRI, to look for signs of damage in the CNS. But MS is not the only cause of lesions. Radiologists review every MRI and look for signs of diseases. An MRI report may include lists of all possible conditions that could explain the results.1-3

An MRI with lesions does not mean you definitely have MS. For a final MS diagnosis, a doctor will typically use a physical exam and questions about your medical history. They may confirm the diagnosis or rule out other conditions with other tests like bloodwork or a spinal tap.1-3

If you are already diagnosed with MS, your doctors may use MRI images to look for evidence of ongoing disease activity such as new lesions. Current MS disease modifying therapies help prevent development of new lesions. New lesions on an MRI might suggest your current therapy is not working for you. MRIs taken over time can also show changes in old lesions. Sometimes old lesions can shrink or fade overtime. If lesions are growing or spreading, it may mean you need to consider new treatments.1-3

If you are getting multiple MRIs over time of the same area of your body, try to get the MRIs at the same facility. This helps with tracking because the MRI machine and technique will be more consistent.1-3

You may have access to MRI results before meeting with your doctor. But it can be a good idea to wait to review results with a professional. Doctors are trained to interpret the results and can address any concerns you may have.3

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