Multiple sclerosis (MS) is a condition in which the body’s immune system attacks the protective covering (myelin) surrounding the nerves of the central nervous system (CNS). There’s no single definitive test that can diagnose MS. Diagnosis is based on symptoms, clinical evaluation, and a series of diagnostic tests to rule out other conditions.
A type of imaging test called an MRI scan is an important tool in diagnosing MS. (MRI stands for magnetic resonance imaging.)
MRI can reveal telltale areas of damage called lesions, or plaques, on the brain or spinal cord. It also be used to monitor disease activity and progression.
If you have symptoms of MS, your doctor may order an MRI scan of your brain and spinal cord. The images produced allow doctors to see lesions in your CNS. Lesions show up as white or dark spots, depending on the type of damage and the type of scan.
MRI is noninvasive (meaning nothing is inserted into a person’s body) and doesn’t involve radiation. It uses a powerful magnetic field and radio waves to transmit information to a computer, which then translates the information into cross-sectional pictures.
Contrast dye, a substance that’s injected into your vein, can be used to make some types of lesions show up more clearly on an MRI scan.
Although the procedure is painless, the MRI machine makes a lot of noise, and you must lie very still for the images to be clear. The test takes about 45 minutes to an hour.
It’s important to note that the number of lesions shown on an MRI scan doesn’t always correspond to the severity of symptoms, or even whether you have MS. This is because not all lesions in the CNS are due to MS, and not all people with MS have visible lesions.
MRI with contrast dye can indicate MS disease activity by showing a pattern consistent with inflammation of active demyelinating lesions. These types of lesions are new or getting bigger due to demyelination (damage to the myelin that covers certain nerves).
The contrast images also show areas of permanent damage, which can appear as dark holes in the brain or spinal cord.
Following an MS diagnosis, some doctors will repeat an MRI scan if troubling new symptoms appear or after the person begins a new treatment. Analyzing the visible changes in the brain and spinal cord may help assess current treatment and future options.
Your doctor may also recommend additional MRI scans of the brain, the spine, or both at certain intervals to monitor disease activity and progression. The frequency with which you need repeat monitoring depends on the type of MS you have and on your treatment.
MRI will show different things based on the type of MS involved. Your doctor can make diagnostic and treatment decisions based on what your MRI scan shows.
Clinically isolated syndrome
A single neurologic episode caused by inflammatory demyelination and lasting at least 24 hours is called clinically isolated syndrome (CIS). You may be considered at high risk of MS if you’ve had CIS and an MRI scan shows MS-like lesions.
If this is the case, your doctor may consider starting you on a disease-modifying MS treatment because this approach may delay or prevent a second attack. However, such treatments have side effects. Your doctor will weigh the risks and benefits of treatment, considering your risk of developing MS, before recommending disease-modifying treatment after an episode of CIS.
Someone who has had symptoms but no MRI-detected lesions is considered at lower risk of developing MS than those who have lesions.
People with all forms of MS can have lesions, but people with a common type of MS called relapsing-remitting MS generally have recurrent episodes of inflammatory demyelination. During these episodes, active areas of inflammatory demyelination are sometimes visible on an MRI scan when contrast dye is used.
In relapsing-remitting MS, distinct inflammatory attacks cause localized damage and accompanying symptoms. Each distinct attack is called a relapse. Each relapse eventually subsides (remits) with periods of partial or complete recovery that are called remissions.
Primary progressive MS
Rather than intense bouts of inflammatory demyelination, progressive forms of MS involve a steady progression of damage. The demyelinating lesions seen on an MRI scan may be less indicative of inflammation than those of relapsing-remitting MS.
With primary progressive MS, the disease is progressive from the start and doesn’t involve frequent distinct inflammatory attacks.
Secondary progressive MS
Secondary progressive MS is a stage that some people with relapsing-remitting MS will progress into. This form of MS is classified into stages of disease activity and remission, along with new MRI activity. Additionally, secondary progressive forms include stages during which the condition worsens on a more gradual basis, similar to primary progressive MS.
If you have what you think may be MS symptoms, talk to your doctor. They may suggest that you get an MRI scan. If they do, keep in mind that this is a painless, noninvasive test that can tell your doctor a lot about whether you have MS and, if you do, what kind you have.
Your doctor will explain the procedure to you in detail, but if you have questions, be sure to ask them.