MS is a condition in which the immune system attacks the protective covering of the nerves in your brain and spinal cord. These damaged areas are called lesions and are part of an MS diagnosis.

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The protective covering around nerves in your brain and spinal cord is called myelin. It allows your nerves to quickly transmit electrical signals throughout your body.

Multiple sclerosis (MS) develops when your immune system attacks myelin cells and disrupts nerve signals. Researchers don’t know why MS occurs, but it’s thought that genetics and environmental factors both play a role.

You can see some of the demyelination with magnetic resonance imaging (MRI). The appearance of demyelination is often described as lesions. A doctor may diagnose you with MS if they can see lesions in multiple parts of your central nervous system, with evidence that they formed at separate times.

Learn more about MS.

To make an MS diagnosis, doctors need to see evidence of brain or spinal cord lesions on MRI scans.

The gold standard guidelines for diagnosing MS are called the McDonald criteria. These guidelines were last updated in 2017.

According to the current version of these guidelines, MS can be diagnosed if:

  • you have two lesions and have at least two symptom flare-ups, also called attacks
  • you have two attacks, one lesion, and evidence of an attack in a different area of your central nervous system
  • you have one attack and two lesions with evidence of lesions forming at different times in the same location or the presence of proteins called oligoclonal bands in your spinal cord is confirmed with a lumbar puncture
  • you have one attack, one lesion, and evidence of damage occurring at different times and locations
  • worsening symptoms of lesions and evidence of disease in at least two of these areas: brain, spine, spinal fluid

Lesions can heal, though, meaning that some people with MS may not have obvious lesions all the time, especially with effective treatment. However, the presence of lesions remains a key part of the diagnostic criteria for MS.

“Lesion” is a medical term that refers to an area of damaged bodily tissue. An MS lesion is an area in your brain or spinal cord where your immune system damages the protective myelin sheath around your nerves and causes inflammation. They’re also referred to as MS plaques.

MS lesions slow down or block electrical activity from your nervous system and lead to MS symptoms like vision problems or numbness. Some symptoms may be temporary if the inflammation subsides or permanent if scar tissue forms.

Lesions can occur anywhere in your central nervous system, which consists of your brain and spine. The symptoms that you develop depend on where lesions form. Symptom severity largely depends on the location and size of the lesion.

Learn more about MS symptoms.

MRI is the most important tool for diagnosing and tracking the progress of MS. It allows doctors to see the size and location of lesions.

MRI is an imaging technique that uses a strong magnetic field to create detailed images of your body. MRI has a sensitivity of up to 95%, meaning that it can correctly identify lesions up to 95% of the time.

Learn more about how MS is diagnosed.

MS is a progressive condition that can cause the recurring development of lesions.

About 80% to 90% of people diagnosed with MS have relapsing-remitting MS. This type of MS is characterized by periods where new lesions cause worsening symptoms and periods where the lesions heal and symptoms improve.

The other 10% to 20% of people diagnosed with MS have primary progressive MS. This form is characterized by the gradual worsening of symptoms without periods of remittance where symptoms improve.

Learn more about types of MS.

MS can’t be diagnosed with any one test, and misdiagnosis remains a problem. Studies suggest that 30% to 67% of people referred to MS specialty centers with a questionable MS diagnosis are ultimately found not to have MS.

MS symptoms vary between people depending on which nerves are affected. Symptoms can mimic many other conditions, such as:

Here are some frequently asked questions that people have about MS and MS lesions.

Is there a cure for MS?

At this time, there’s no cure for MS, but medications can help reduce the frequency and severity of MS flare-ups and slow the progression of the disease. Researchers are continuing to investigate potential treatment options and are hopeful that they’re moving closer to a cure.

Learn more about MS treatment.

Can MS lesions be reversed?

Your body has a limited ability to repair myelin damage and reverse MS lesions. Researchers are continuing to examine new treatments, such as stem cell therapy, that might one day be able to reverse damage caused by MS.

Do lesions always cause symptoms?

Lesions often don’t cause any symptoms. It’s not uncommon for an MRI to reveal many different lesions that have never caused symptoms.

MS is a disease that develops when your immune system attacks the protective sheath surrounding your nerves called myelin. Damaged areas of myelin are called lesions.

A diagnosis of MS requires evidence of lesions with imaging. Lesions can develop anywhere in your central nervous system, and symptoms vary depending on where lesions form and how severe they are.