How Multiple Sclerosis Is Diagnosed

Man receiving MRI to diagnose multiple sclerosis
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Diagnosing multiple sclerosis (MS) is complex and challenging, mostly because MS symptoms are unique to each individual, and they can mimic those of a number of other diseases. In addition, there is no single blood test, physical exam finding, or imaging test for diagnosing MS.

Today, neurologists use the McDonald Criteria to diagnose MS. This set of guidelines was revised in 2010 to incorporate MRIs into the diagnosis process. The good news about this is that people with MS are now being diagnosed earlier—this means people can begin treatment earlier and potentially slow their disease down.

The McDonald Criteria for Diagnosing MS

The McDonald Criteria revolve around the presence of MS relapses, also known as attacks, flares, exacerbations, or bouts.

An MS relapse refers to either a patient-reported neurological abnormality or a neurological abnormality that is observed on physical examination. This neurological abnormality must be typical of an MS lesion in the central nervous system, which is the brain, spinal cord, and optic nerve. This is something your neurologist will know.

According to the McDonald criteria, in order to be diagnosed with MS, there must be evidence of an MS relapse that occurred in at least two distinct areas of the central nervous system. In addition, these MS relapses must be separated by a month's time.

The diagnosis of MS can be made clinically, meaning simply through a person's symptoms, even if their relapse occurred in the past—although this can only be for one relapse, the other must be current. Also, one of their relapses must be confirmed either by a neurological examination, visual evoked potentials, or an MRI.

Alternatively, a diagnosis can be made through a combination of clinical findings and evidence of an MS lesion on an MRI. Even if a person meets the McDonald criteria, neurologists will often perform other tests like blood work, a lumbar puncture, and visual evoked potentials to confirm the diagnosis and rule out illnesses that may mimic MS.

In other words, a neurologist wants to be certain he is making the correct diagnosis and that there is no alternative explanation—makes sense, right? The last thing you want is to be diagnosed with MS when you really don't have it. So a neurologist wants to be certain, and we are glad for that, even if it means lots of tests.

Factors Considered and Methods Used to Diagnose MS

Here is a closer look at the tools your doctor will use to both diagnosis MS and rule out alternative diagnoses:

Medical History

The doctor will ask a number of questions about the symptoms that you are currently experiencing and any that you have experienced in the past. It's a good idea to make a “symptom log” before you see the doctor, listing any sort of symptom that you have had in the past, how long it lasted, and other information about it. Be sure to list all symptoms, even if previous doctors told you there was nothing wrong.

In addition, take all other medical information along, including which prescription drugs you are on, and any medical test results you may have had in the past.

You will also be asked several questions about the medical history of relatives, drug and alcohol use, as well as other prior health issues. All of this information will help a neurologist piece together a picture to help determine if MS is a likely diagnosis.

Neurological Exam

The doctor will be testing for the following:

  • Functioning of the cranial nerves (these control the senses, as well as how you talk and swallow)
  • Coordination
  • Strength
  • Reflexes
  • Sensation

He will do this by having you perform tasks (like touching your nose, then his finger in succession), touching you with various instruments (and having you report a sensation or looking for a response himself) and doing an examination of your eyes. Be assured that these tests do not hurt. The entire test will probably last about 45 minutes but may last as long as two hours.

Magnetic Resonance Imaging (MRI) Scan

MRIs use magnetic waves to produce images of the brain and spinal cord. If MS is suspected, a special contrast material (gadolinium) injection is usually at the time of the scan, as it reacts to areas of inflammation and will "light up" when a lesion is active. This indicates that demyelination is occurring now or within the last several weeks.

The MRI does not hurt, but it can be a strange experience. It helps if you know what to expect during this test. There are also some things you can do to make your experience better.

As mentioned, this is considered the best test for diagnosing MS, as abnormal lesions appear on MRIs in over 95 percent of people with MS. However, 5 percent of people with MS do not have abnormalities that can be detected on an MRI (producing a false negative), and some age-related damage or other conditions, like a migraine or brain trauma, looks like MS lesions (producing a false positive).

Lumbar Puncture

Also called a spinal tap, this test requires that a small amount of cerebrospinal fluid (CSF) be taken from your spinal column via a needle that is inserted between your vertebrae. The doctor will send the fluid for evaluation, looking for the presence of oligoclonal bands (an increased number of certain antibodies) — an indicator of increased immune activity in the spinal fluid.

This test is positive in up to 90 percent of people with MS but is not specific to MS, so a positive result could indicate another disease or disorder. Depending on results from the MRI, neurological exam, and symptom history, it's possible that you may not have to get a lumbar puncture to receive a definitive diagnosis of MS (I didn’t). However, lumbar puncture results can be useful for ruling out other things if there is still a question about diagnosis.

Visual Evoked Potential Testing

Three main types of evoked potential tests are used in the diagnosis of MS. Each of these tests requires that electrodes are attached to your scalp and connected to an electroencephalograph (EEG) to record brainwaves in response to different stimuli. The different tests are:

  • Brainstem Auditory Evoked Potentials (BAEP): A series of clicks are played in each ear through headphones.
  • Visual Evoked Potentials (VEP): A series of checkerboard patterns are displayed on a screen.
  • Sensory Evoked Potentials (SEP): Mild electrical shocks are administered to an arm or leg.

The doctor is looking for both the size of the response and the speed in which the brain receives the signal. Weaker or slow signals may indicate that demyelination has occurred and that MS is a possibility. However, this test is also not specific to MS, meaning abnormalities could indicate another problem. A series of all three tests could take up to two hours to complete.

Blood Tests

There is currently no blood test for MS. Still, a series of tests will be run on your blood to rule out other things, such as Lyme disease, HIV, some rare genetic disorders, and a group of diseases known as collagen-vascular diseases, like lupus.

A Word From Verywell

MS can be a tricky disease to definitively diagnose, and the process often requires patience. With that, it's important to find a neurologist that you feel comfortable with and have confidence in to work on your diagnosis. After all, if you do have MS, this person will likely be your partner in health for a long time.

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Article Sources
  • National MS Society. Diagnosing MS.
  • Polman, C.H., et al. (2011). Diagnostic criteria for multiple sclerosis: 2010 revisions to the McDonald criteria. Annals of Neurology, Feb;69(2):292-302.