McDonald Criteria for MS

The McDonald criteria are guidelines used to help diagnose MS. For this reason, doctors need to take information from several sources to come to a conclusion. The McDonald criteria help sort different types of symptoms, imaging findings, and other test results. This makes it possible to determine whether MS may be the underlying cause.

The McDonald criteria have been revised over time. This has improved their accuracy in diagnosing MS. The most recent updates were made in 2017 by a team of expert neurologists.1-4

What does the McDonald criteria consider?

The information used to diagnose MS using the McDonald criteria includes:1-4

Symptoms and frequency of attacks

Diagnosing MS requires neurological symptoms that point to damage to the central nervous system (CNS). The CNS includes the brain and spinal cord. These symptoms must not be from another cause">from another cause, like an infection or a different autoimmune disorder.

A person’s neurological symptoms may be considered an attack if they last at least 24 hours. A history of symptoms may also point to past attacks.

The first onset of MS-like symptoms is considered clinically isolated syndrome (CIS)">clinically isolated syndrome (CIS). The McDonald criteria can help to diagnose MS from this starting point. They can also help predict the risk of future symptoms.1-4

Dissemination in space

The McDonald criteria require MS-related damage in more than 1 area of the CNS to diagnose MS. This is called dissemination in space. For example, you may have weakness of the right hand and difficulties in vision. The arm and the eyes are controlled by different parts of the brain. This means there is evidence of more than 1 area of the brain being affected.

Another way to prove dissemination in space is imaging. MS-related damage is visible on brain or spinal MRIs. These damaged areas are called lesions. The places where lesions can occur include the space around the ventricles in the brain and the spinal cord. If you have lesions in more than 1 place, this is dissemination in space.1-4

Dissemination in time

In order to diagnose MS, damage must also have happened over time. If you have more than 1 attack over a longer period, like 2 attacks in 2 years, your symptoms have occurred over time. This is called dissemination in time. At least 30 days must pass between attacks for them to be considered separate.

The McDonald criteria do not always require more than 1 attack for MS to be diagnosed. Your doctor can also diagnose MS if you have 1 attack and MRI shows lesions that have occurred at other times. On just a single MRI scan, dissemination in time can be shown if IV contrast is given. Brand new lesions will take up the contrast and appear bright, but older lesions will not. In addition, if you have old MRI scans, your doctor can compare a new scan with an old scan to see if there are new lesions developing over time. 1-4

Using CSF in diagnosis

In some cases, diagnosing MS may be more complex. Tests like CSF studies">CSF studies may be needed. CSF is a colorless fluid produced in the brain. It surrounds the brain and spinal cord, cushioning them and providing important nutrients. Ninety percent or more of those with MS have a protein in their CSF called oligoclonal bands (O-bands).

O-bands can be used to diagnose MS if you have only 1 attack of MS-like symptoms. If your symptoms affect more than 1 area of the brain and O-bands are present, that would be enough to diagnose MS. If your symptoms only affect 1 area of the brain, O-bands and some MS-like imaging findings can still lead to an MS diagnosis.1-4

McDonald criteria and primary progressive MS

The McDonald criteria are usually used to diagnose relapsing-remitting MS. But O-bands can also help to diagnose MS that is progressive since onset. For example, O-bands and at least 1 year of worsening symptoms can lead to a primary-progressive MS diagnosis.1-4

Your doctor can help collect all the required information to figure out whether your condition would be classified as MS. They can also tell you how your symptoms and findings from imaging and CSF fulfill the McDonald criteria.

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