The path to a diagnosis of multiple sclerosis (MS) can be long and uncertain. There is no single, conclusive test that identifies this demyelinating disease, but magnetic resonance imaging (MRI) can be a valuable diagnostic tool. MRI uses a strong magnetic field and radio waves to evaluate the relative water content in central nervous system (CNS) tissue.

An MRI scan provides the most detailed view of the CNS of all imaging techniques, showing the progression, location, and number of MS lesions. MRIs with contrast can differentiate between current inflammation, newer brain lesions, and older sites of permanent damage. MRI scans can also reveal any myelin damage or injury to the CNS that is not causing symptoms, known as silent damage.

Most MS diagnoses are partially based on MRI findings over time. After a diagnosis is made, people with MS typically continue receiving regular scans to track disease activity.

What Role Does MRI Play in MS Diagnosis?

Although no single test can definitively lead to an MS diagnosis, MRI is invaluable to the process. The visual detection of the MS plaques in the brains of people with multiple sclerosis has removed much of the guesswork from the process. Still, even MRI results don’t provide 100 percent of the diagnostic picture.

MRI scans don't show everything that's happening in a person's body or the entire central nervous system. It's all a matter of what part of the CNS is photographed and when. Some abnormalities may be missed by the scan, depending on when the imaging is performed. The absence of lesions on MRI cannot definitively rule out a possible diagnosis of MS.

Although MRI can help doctors detect MS, multiple sclerosis is a clinical diagnosis, which means that people who are suspected of having the condition should also be prepared to provide doctors with the most detailed account of their medical history possible. In addition, a physician will perform a complete neurological exam during the diagnosis process.

During the neurological exam, you might be asked to push against the doctor’s hands to show your strength and dexterity, or you may be tested on your sense of taste, smell, and hearing. The results help doctors understand whether problems are coming from the central nervous system, the peripheral nervous system (nerves that branch off from the spinal cord), or the autonomic nervous system (which regulates blood pressure, breathing, and digestion, among other automatic processes).

During the diagnosis process, you might also undergo evoked potential (EP) tests, which are sometimes useful in diagnosing MS. During a somatosensory EP test, people receive minor, painless shocks to their arms and legs. The diagnostic team would also order lab work such as blood tests to exclude other possibilities.

What Do Doctors Look For on an MRI Scan?

When a doctor orders an MRI protocol for someone who may have MS, they are looking for specific changes in the brain. MRI is sensitive to differences in brain tissue and can provide doctors with the insight they need for a proper diagnosis.

Specifically, the MRI shows lesions in the brain’s white matter, which is part of the central nervous system. It may also show changes in or around the cortex or to the brain stem, and may reveal spinal cord lesions.

According to the Cleveland Clinic, neurologists will often order an MRI a year after treatment for MS has begun, or when unexplained or unexpected changes require another look.

How Is MRI Used To Evaluate Disease Progression and Treatment Effectiveness?

Scientific advances in the past two decades help doctors diagnose MS much earlier than they could in the past. Diagnosis of MS is based on the McDonald criteria, named after neurologist Dr. Ian McDonald. Dr. McDonald first noted that MRI scans could offer insight into the nature and progression of inflammatory brain diseases such as MS.

The McDonald criteria stipulate that two conditions are essential for the diagnosis of MS:

• First, there must be evidence of damage to the central nervous system "disseminated in time," meaning that the damage has occurred on different dates.
• Second, there must also be evidence of harm "disseminated in space," or found in at least two different parts of the CNS.

These criteria put a bigger spotlight on the role of MRI results as part of the diagnosis. In some cases, however, the MRI may instead lead to a diagnosis of clinically isolated syndrome (CIS). This syndrome is said to be one of the MS disease courses, but in CIS, only one location is affected. In some cases, those with CIS have a single lesion that shows up on MRI, which is the one that is creating symptoms for them.

What To Expect During Your First MRI Scan

A brain MRI scan is painless. However, it can be very loud inside the machine. People getting MRI scans are advised to wear earplugs to protect their ears. They should also be sure to report any metal content in their bodies, such as orthopedic hardware, pacemaker devices, piercings, or shrapnel.

In addition, it’s important to note that your first MRI scan may be just one in a series of imaging tests throughout your MS journey. Even following your diagnosis, your physician may order MRI again in the future to track your disease progress and make treatment recommendations.

You Are Not Alone With Multiple Sclerosis

By joining MyMSTeam, the social network and online community for those living with multiple sclerosis, you gain a support group of more than 167,000 people who know what it’s like to depend on MRI scans as part of the diagnosis and treatment journey.

How often does your doctor schedule MRI scans? How do you manage anxiety about what the results will show? Comment below or post on MyMSTeam.