Guidelines for MS diagnosis: McDonald criteria

Last updated Oct. 13, 2025, by Marisa Wexler, MS
Fact-checked by Ines Martins, PhD

An early diagnosis of multiple sclerosis (MS) is important but can be complex, as its symptoms often resemble those of other neurological disorders. To help clinicians confirm the disease more accurately and earlier, experts have developed a set of diagnostic guidelines known as the McDonald criteria.

What are the McDonald criteria?

MS is an autoimmune disease in which the immune system mistakenly attacks parts of the central nervous system (CNS), which includes the brain, spinal cord, and optic nerves. This damage disrupts communication between the brain and body, leading to a wide range of symptoms.

The McDonald criteria are a set of internationally recognized guidelines that incorporate clinical and laboratory evaluations, as well as MRI scans and other tests, to establish an MS diagnosis.

The first version was published in 2001 by an international team led by neurologist Ian McDonald. The criteria have since been updated several times to reflect advances in MS research and imaging technology. The most recent revision took place in 2024.

What features are included in the McDonald criteria?

The 2024 update to the McDonald criteria outlines several scenarios where an MS diagnosis can be established, depending on the patient’s symptoms and test results. To confirm MS, doctors will look for evidence that disease activity has affected the CNS in characteristic ways.

Four main types of evidence can be assessed:

• Dissemination in space: Signs of nerve damage appearing in multiple regions of the CNS.
• Dissemination in time: Evidence that damage has occurred at different points in time.
• Characteristic MRI features: Specific patterns of lesions, such as the central vein sign (CVS) and paramagnetic rim lesions (PRLs).
• Cerebrospinal fluid (CSF) findings: Laboratory evidence of immune activity in the CNS, such as oligoclonal bands (OCBs) or kappa free light chains (kFLCs).

Dissemination in space

Dissemination in space means that nerve damage has occurred in more than one area of the CNS. According to the 2024 McDonald criteria, dissemination in space is demonstrated by the presence of lesions in at least two of five specific CNS regions. These regions include:

• the periventricular, juxtacortical or cortical, and infratentorial regions of the brain
• the optic nerves, which carry visual information from the eyes to the brain
• the spinal cord

In people with gradually worsening MS-like symptoms for at least one year — suggestive of progressive MS — the presence of two or more spinal cord lesions is sufficient to fulfill the criteria for dissemination in space, even if no other regions are affected.

MRI scans of the brain and spinal cord are the main tools used to evaluate dissemination in space. Eye imaging and functional tests, such as optical coherence tomography and visual evoked potentials may also be used to detect optic nerve involvement.

Dissemination in time

Dissemination in time means that neurological damage has happened at more than one point in time. This can be demonstrated by:

• the occurrence of more than one relapse
• the appearance of new lesions on follow-up MRI scans
• clear-cut evidence of brain damage that happened at different times (i.e., new inflammatory lesions alongside older lesions that are no longer actively inflamed)

Characteristic MRI features

Certain MRI findings are highly suggestive of MS and may strengthen diagnostic confidence when used alongside other diagnostic features. These include:

• PRLs, or areas of tissue damage surrounded by a ring of iron-laden immune cells, indicating chronic inflammation. A person with at least one PRL is considered PRL positive.
• CVS, or lesions that contain a small blood vessel at their center. Having at least six lesions with CVS is enough to consider that a person is CVS positive.

Both features are common in MS but rare in other conditions, making them useful in distinguishing MS from other diseases. The 2024 revision formally recognizes that these markers can help support an MS diagnosis in certain situations.

CSF findings

Testing the CSF, or the liquid that surrounds the brain and spinal cord, can provide additional diagnostic evidence. Two key markers characteristically detected in the CSF are:

• OCBs
• kFLCs

The presence of these proteins in the CSF is indicative of abnormal immune activity within the CNS. According to the 2024 McDonald criteria, OCBs and kFLCs can be used interchangeably to demonstrate this inflammation and support an MS diagnosis in certain situations.

How are the McDonald criteria used to diagnose MS?

According to the 2024 McDonald criteria, MS can be diagnosed in people who have typical symptoms of the disease and evidence of any of the following:

• both dissemination in space and dissemination in time
• dissemination in space plus a positive CSF test (OCBs or kFLCs)
• dissemination in space plus CVS positivity
• lesions in at least four of the five regions used to evaluate dissemination in space

If lesions are seen in only one of the five CNS regions in someone with MS-like symptoms, MS can still be diagnosed if one of the following is present:

• a positive CSF test together with MRI signs of CVS or PRLs
• dissemination in time plus evidence of CVS or PRLs

In previous versions of the McDonald criteria, MS could only be diagnosed if patients were experiencing MS-like symptoms. People with MRI findings suggestive of MS but without symptoms were classified as having radiologically isolated syndrome (RIS).

However, under the 2024 update, MS can be diagnosed in some individuals who previously would have been labeled as RIS. Specifically, a diagnosis can be made if patients show dissemination in space and at least one of the following:

• dissemination in time
• a positive CSF test
• CVS positivity

Importantly, the guidelines emphasize that MS should only be diagnosed when no better explanation exists for a person’s symptoms or test results. For that reason, clinicians often perform additional tests to rule out other neurological or inflammatory diseases before confirming an MS diagnosis.

What does the updated version of the McDonald criteria mean for MS patients?

The updated 2024 McDonald criteria, which builds on the previous 2017 revision, do not change or invalidate existing MS diagnoses made under earlier versions. Instead, the update aims to reflect advances in MS research and imaging technology to help clinicians make earlier and more accurate diagnoses, reducing both wait times and the risk of misdiagnosis.

2024 revisions to the McDonald criteria

The 2024 update introduces several important changes from the 2017 version:

• In the previous version, only four areas of the CNS — three brain regions and the spinal cord — could be used to demonstrate dissemination in space. The new version adds the optic nerve as the fifth region that can now be considered.
• Under the old criteria, a diagnosis of MS required evidence of dissemination in time. The 2024 update removes this requirement, allowing MS to be diagnosed in patients with only one clear instance of disease activity, if other supporting evidence is present.
• The new version formally introduces guidance on the use of CVS and PRLs as supporting imaging markers. These findings are highly specific to MS but were not included in prior versions.
• While the earlier version included guidance on the use of OCBs to diagnose MS, the 2024 criteria now include kFLCs as an equivalent biomarker. Because kFLC testing is automated and widely available, it may make diagnosis faster and more consistent across centers.
• Previously, MS could only be diagnosed in people who had typical MS symptoms. The new guidelines allow a diagnosis in asymptomatic individuals who meet other diagnostic criteria, expanding the potential for earlier intervention.

A unified framework for diagnosing all types of MS

One of the most significant changes in the 2024 McDonald criteria is the introduction of a single, unified framework for diagnosing all forms of MS.

Historically, MS has been divided into two broad categories:

• relapsing MS, marked by relapses or flares where symptoms suddenly worsen
• progressive MS, characterized by a gradual worsening of symptoms over time, independent of relapses

Earlier versions of the McDonald criteria used different diagnostic pathways for these forms of the disease. However, growing evidence now shows that relapsing and progressive MS exist on a continuum, with overlapping biological mechanisms and imaging features. The 2024 revision recommends using one consistent approach to diagnose MS, regardless of whether a person’s symptoms appear relapsing or progressive.

The update also eliminates separate diagnostic criteria for adults and children. Instead, it presents a unified set of guidelines applicable to patients of all ages.

Still, the criteria emphasize that clinicians should exercise caution when diagnosing older adults who may have other conditions that can mimic MS, as these can increase the risk of misdiagnosis.

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