Tools Your Doctor Will Use to Make a Diagnosis of MS

The diagnosis of MS is a clinical one based primarily on patient medical history and neurologic exam. No single set of symptoms or laboratory test, such as a blood test, imaging test, genetic test, or immune function test, can independently identify the presence of MS. However, several tools are available to help confirm a diagnosis of MS.  Specific tests which may be used include magnetic resonance imaging (MRI), visual evoked potential (VEP) testing, or analysis of cerebrospinal fluid which is retrieved by lumbar puncture.

How are medical history and neurologic exam used to diagnose MS?

In completing your medical history, the doctor collects information regarding past or present symptoms suggestive of MS. Symptoms may include fatigue, weakness, vision problems, difficulty walking, problems with bladder control, or uncomfortable sensations including numbness or “pins and needles.” As part of the medical history, the doctor will also ask about family history of disease, places where you have lived, any history of substance use or smoking, and information regarding any medications you may be taking.

In addition to subjective evidence of disease (ie. symptoms which the patient reports), the doctor will conduct a thorough neurologic examination to measure objective evidence suggestive of MS. Objective signs of MS may be as subtle as abnormal eye movements or pupil response, spasticity or weakness in the limbs, sensory disturbances, and abnormal reflex responses.

In some cases, information collected from the medical history and neurologic exam are sufficient to satisfy the diagnostic criteria for MS. However, the doctor will typically use one or more of the following tests to confirm a diagnosis of MS.

How is magnetic resonance imaging or MRI used to diagnose MS?

Magnetic resonance imaging (MRI) is the best imaging technique for detecting the type of CNS damage that occurs in MS. Areas of damage called plaques or lesions can be visible on certain types of MRI scans which can also distinguish between old and new lesions with the use of an injected contrast agent, Gadolinium. While MRI is a valuable tool in confirming an MS diagnosis, a small percentage of people with MS (about 5%) will have no evidence of lesions visible on an MRI scan.

How is visual evoked potentials or VEP testing used to diagnose MS?

Evoked potentials (EP) tests are used to record and measure electrical impulses which travel through specific sensory pathways of the nervous system in response to stimuli. When you hear a loud noise, your nervous system sends an electrical signal or impulse through the auditory (hearing) pathway of your nervous system. Similarly, when you see an image, your nervous system sends an impulse through the visual pathway.

The damage caused by MS (demyelination) leaves scars (lesions) in places that the protective coating on nerves (myelin) has been stripped. Myelin not only protects the nerve cells, it also helps to transmit nerve impulses. Where myelin is damaged, nerve signals may travel more slowly or not at all. Results of EP testing can provide evidence of damage to nerve pathways that may be subclinical (not detected during neurologic exam). Different types of EP tests may be used, including somatosensory evoked response/potential (SSEP), auditory brain stem evoked response/potential (ABEP) and visual evoked response/potential (VEP). Results of VEP tests are abnormal in about 90% or 9 out of 10 people with MS making it the most useful EP in confirming a diagnosis of MS.

How is cerebrospinal fluid analysis used to diagnose MS?

In some situations, analysis of a patient’s cerebrospinal fluid (CSF) may be needed to confirm a diagnosis of MS. CSF, the fluid that surrounds and bathes the spinal cord and brain is obtained during a lumbar puncture, a procedure that involves insertion of a needle into the lower spine to withdraw enough fluid for chemical analysis. The CSF is tested for the presence of certain cells and proteins, including oligoclonal band (O-bands), which indicate the kind of abnormal immune response seen in MS. Analysis of CSF may not be required to make an MS diagnosis, but can be useful in ruling out other diseases.

Is there a blood test for diagnosing MS?

There is no blood test for diagnosing MS. However, blood tests can be used to rule out other diseases and health problems which cause symptoms similar to those associated with MS. Examples of diseases to rule out include Lyme disease, AIDS, collagen-vascular diseases, and some rare hereditary disorders.

Written by: Jonathan Simmons | Last reviewed: May 2015.
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