Tools Your Doctor Will Use to Make a Diagnosis of MS

MS is a clinical diagnosis. This means there is no single test that can diagnose it. Instead, your doctor (usually a neurologist) will use many different types of information to assess your symptoms. The process starts with taking a thorough medical history and performing a neurological exam. Most people will also undergo central nervous system (brain and spinal cord) imaging. If the diagnosis is still unclear, evoked potentials tests and studies of the cerebrospinal fluid (CSF) may be used.1

Taking a history

The first step on the path to diagnosis is collecting a full symptom and medical history. Your doctor will ask about your specific symptoms and how long they have been occurring. They will also ask about past episodes of neurological symptoms. These will include symptoms both similar to and different from the ones you currently have. For example, if you currently have vision problems, but 3 months ago you had arm weakness or tingling, your doctor will want to know about both episodes.

Your doctor will also ask about any other medical conditions you have and what medicines you take. They may also ask about any recent illnesses or people around you who are sick. Sometimes, certain infections can present like MS. Doctors also ask if there are any medical conditions in your family. Family history may be helpful in determining what conditions you are at risk for. For example, a family history of MS or other autoimmune conditions may place you at a higher risk. Other neurological conditions in the family, like stroke, may also be helpful to know about.

Full neurological exam

After a full history is taken, a neurological exam will be performed. Your doctor will assess strength and sensation throughout your body. They will also pay special attention to your cranial nerves. These are 12 pairs of nerves that serve many functions in the head and neck. Cranial nerves are often impacted in MS.

Your doctor will also assess your coordination, your mental status, and the way you walk. They will also test a variety of reflexes. Any abnormalities in your neurological exam may point toward an underlying condition. In some cases, symptoms and exam findings are so specific that your doctor may be able to determine which exact area of the brain or spinal cord is impacted.2

Magnetic resonance imaging

Imaging of the brain and spinal cord can also be helpful in diagnosing MS. MS-related damage and inflammation can cause abnormal findings on MRI. These are called lesions. Lesions that are brighter on imaging indicate more recent inflammation. Lesions that are darker often represent older areas of damage. Lesions in different areas of the brain or that are of different ages may point toward MS.3,4

The McDonald criteria is a set of guidelines used to help diagnose MS based on symptoms and imaging findings. Doctors use these guidelines like a checklist to determine whether MS is the underlying cause of a person’s symptoms. The goal of the McDonald criteria is to identify MS-related symptoms and imaging findings that show MS damage has been occurring over time and in different areas of the brain. If the diagnosis is still unclear, CSF studies may also be helpful.5

CSF analysis

CSF is collected through a process called a lumbar puncture (also called a spinal tap). During this procedure, a needle is inserted through the back and into the spinal cord to collect a small sample of spinal fluid. Not all people with MS-like symptoms will undergo a lumbar puncture. However, as mentioned, it can be helpful in situations in which the diagnosis is unclear. Doctors will look for the presence of a specific protein in the CSF called oligoclonal bands (O-bands). CSF studies can also help rule out other neurological issues like meningitis.6

Evoked potentials testing

Evoked potentials tests measure the response of the nervous system to different stimuli. In these tests, the nerves in specific sensory pathways are stimulated. This includes vision, hearing, and touch. As an example, nerves involved in the visual pathway may be triggered by flashing lights or different patterns on a screen. The speed at which these nerves respond and how strongly they respond can be measured.

In some cases, MS-related nerve damage may be present but is not severe enough to cause noticeable symptoms. This damage may be so subtle it is not even picked up on a neurological exam or on MRI. Evoked potentials tests can be used to detect nerve problems in these cases.3

Is there a blood test for diagnosing MS?

At this time, there is no blood test to diagnose MS. However, blood tests may be helpful in ruling out other similarly presenting conditions. Some of these include Lyme disease, vitamin deficiencies, certain infections, lupus, HIV, and more.

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Written by: Casey Hribar | Last reviewed: June 2021.