McDonald criteria

The McDonald criteria is the set of international guidelines used by neurologists to help diagnose multiple sclerosis (MS) accurately as early as possible. They were first developed in 2001 by an international panel of experts led by the neurologist Professor Ian McDonald. Since then, they have been revised several times to reflect advances in our understanding of MS. The most recent update was completed in 2024 and published in September 2025.

On this page we look at how neurologists use the criteria to help them diagnose MS, the evidence they are looking for and the additional signs that can be used to help make a diagnosis more quickly.

The McDonald criteria are the guidelines that neurologists use in combination with your medical history and a range of other tests to help establish whether you have multiple sclerosis (MS) or not. 

MS can be difficult to diagnose as there isn’t a simple test that can tell you if you have MS, and the symptoms are not unique to the condition. So, the McDonald criteria were developed to help neurologists make an accurate diagnosis of MS as quickly as possible. An earlier diagnosis means treatment can be started sooner. This can prevent permanent damage and improve your long-term outcomes, such as fewer relapses, slower progression and less severe disability.

Our understanding of how MS presents and progresses in individuals is constantly evolving. In recent years there have been advances in:

• the tests for MS – including advanced MRI techniques and using optical coherence tomography (OCT) scans 
• the evidence that can diagnose MS – such as recognising the optic nerve (which connects the eye to the brain) as a fifth location for detecting MS activity, discovering MS-specific lesions which are rarely seen in other conditions, and identifying new biomarkers that can show MS-related inflammation
• the way we think about MS as a condition – with a move towards thinking of MS as a single condition rather than three separate types (relapsing remitting, primary progressive and secondary progressive).

The criteria are updated to reflect these developments so that MS can be diagnosed more accurately and more quickly.

When you visit your neurologist for the first time, they will ask you about the symptoms you have experienced and carry out a neurological examination. These are simple physical tests including checks of your vision, strength and coordination. Using the McDonald criteria, they can assess what other evidence they need to gather so they can make an accurate diagnosis of MS or rule it out as the cause of your symptoms. 

The criteria tell the neurologist where and how to look for evidence of MS. This might involve having further investigations such as blood tests, a magnetic resonance imaging (MRI) scan or a lumbar puncture.

We have more information on the tests used in the diagnosis of MS. 

Watch Professor Alasdair Coles explain how the McDonald criteria are used to diagnose MS:

To give a diagnosis of MS, the neurologist typically looks for evidence of damage to the central nervous system (CNS) that has occurred in different areas of the brain and/or spinal cord (dissemination in space, or DIS) and at different times (dissemination in time, or DIT). This generally distinguishes MS from other similar demyelinating neurological conditions. 

The evolution of the criteria over the years means that although there must always be evidence of DIS, there are some circumstances where evidence of DIT may no longer be needed to confirm a diagnosis.

To make a diagnosis of MS, neurologists must find evidence that MS activity (episodes of inflammation) has occurred in more than one area in the brain and/or spinal cord. This demonstrates what’s known as ‘dissemination in space’. There must always be evidence of DIS for an MS diagnosis to be made.

Evidence of dissemination in space (DIS) can be shown if you have an MRI scan that shows lesions in specific parts of your brain or anywhere in the spinal cord.

Your medical history and neurological examination can indicate that different areas of your body have been affected and point towards dissemination in space. For example, you might have had problems with your vision and also have weakness in your arms or legs. But you need to have evidence of lesions for a diagnosis to be made.

An MRI scan can be used to look for evidence of lesions that are typical for MS. The five areas neurologists focus on when looking for lesions to show evidence of DIS are: 

• touching the fluid spaces in the centre of the brain (periventricular)
• in or touching the outermost brain layer or cortex (cortical/juxtacortical)
• in the brainstem or cerebellum (infratentorial)
• the spinal cord
• the optic nerve (the nerve at the back of each eye that sends messages to the brain).

Damage to the optic nerve can be demonstrated through visual evoked potential (VEP) and optical coherence tomography (OMT) tests, as well as by MRI scan.

Neurologists define areas in your central nervous system in a way that means closely linked areas (topologies) count as one place. The dissemination in space criteria are fulfilled if lesions consistent with MS are found in two or more of the five regions described above, even if they are not causing symptoms. If you have lesions in four or more of the five sites, it may be possible to make a diagnosis without the need for further tests, in an appropriate clinical context. For example, you have had a clinical presentation typical for MS.

In individuals who experience progressive symptoms from the start, evidence of two or more spinal cord lesions is enough to fulfil DIS. In this situation MS can be diagnosed without brain lesions.

To demonstrate dissemination in time (DIT), the neurologist is looking for evidence that you have had MS activity (episodes of inflammation) on more than one occasion, rather than a single episode. This can be shown if:

• you’ve had relapses at different points in time
• an MRI scan shows new lesions when compared to a previous scan
• active (enhancing) lesions can be seen on the same scan as older (non-enhancing) lesions
• a cerebrospinal fluid sample (from a lumbar puncture) is positive for oligoclonal bands (OCBs) that are absent in a concurrent blood sample, or kappa free light chains (kFLCs) showing you’ve had inflammation for a while.

In the current criteria, there are some circumstances where demonstrating dissemination in time is no longer required to make a diagnosis of MS. This might be because the neurologist can see other signs such as a specific number, type or location of lesions which allows them to make the diagnosis. 

For example, if you have experienced a typical relapse, or had progressive symptoms for at least 12 months, and have typical lesions in at least four of the five regions that show dissemination in space, you can be given a diagnosis of MS without needing to show dissemination in time.

The current criteria recognise some additional signs that can be used as evidence to help diagnose MS in some situations. The addition of these signs to the criteria means that, for some people, the diagnosis may be made more quickly, or further tests may not be needed. It may also mean that some people who have only had one episode of neurological symptoms (known as clinically isolated syndrome or CIS) may no longer need to wait for further activity to happen at later date to receive a diagnosis.

MS lesions often have a blood vessel running through the middle of them which can sometimes be seen on a specialised MRI scan. This is known as the central vein sign (CVS). It can be used as a diagnostic marker for MS.  The CVS can help differentiate MS lesions from lesions caused by other conditions such as migraine (NHS.UK).

In some circumstances, the presence of lesions with the CVS can be used to help make a diagnosis more quickly. For example, if you have lesions in at least two locations within the brain and/or spinal cord, and six or more lesions show the CVS, you can be diagnosed with MS. If you have fewer than 10 brain lesions in total, but the majority show the CVS, MS can diagnosed even if there are fewer than six CVS positive lesions.

Another example of when the CVS can be used to confirm a diagnosis is if you have experienced a typical clinical relapse or progression but only have evidence of lesions in one of the five locations. If you are also positive for CVS and show dissemination in time on MRI or have a positive cerebrospinal fluid (CSF) result, you can now be diagnosed with MS.

Some active MS lesions have a very distinctive dark rim of iron around their edge which can be seen on some MRI scans. They are known as paramagnetic rim lesions (PRLs), and like the central vein sign (CVS), they are highly specific for MS and are rarely seen in other conditions. 

The presence of PRLs can be used to confirm a diagnosis of MS in some situations. For example, if you have experienced a typical clinical relapse or progression but only have evidence of lesions in one of the five locations, you can be diagnosed with MS if you have one or more PRLs and show dissemination in time on MRI or have a positive cerebrospinal fluid (CSF) result.

Watch Professor Alasdair Coles explain how new MRI markers can help diagnose MS earlier: 

The criteria include additional guidance on diagnosing MS in children, adults over 50 and those who are more at risk of conditions affecting the blood vessels (vascular disease). This is to reduce the risk of misdiagnosis in these groups.

In children (those under 18), there is guidance on differentiating MS from other conditions such as testing for antibodies to exclude myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) (GOSH NHS Foundation Trust). As well as this, if the central vein sign is present in more than half of lesions in a child, this may be enough for an MS diagnosis to be made.

In older adults (over 50) and individuals with vascular risk factors, such as smoking or high blood pressure, additional evidence may be needed to make an MS diagnosis. In particular:

• a spinal cord lesion
• signs of inflammation in the cerebrospinal fluid  – such as oligoclonal bands or kappa free light chains
•  the presence of central vein sign.

MRI scans (NHS.UK) can be carried out for a variety of reasons, for example if you experience frequent headaches or migraines, to diagnose joint injuries or to detect tumours. Sometimes people who have an MRI for another reason find their results show evidence of lesions that are typical for MS, even though they have never experienced typical symptoms. This is known as radiologically isolated syndrome (RIS). In some individuals, RIS is the earliest detectable stage of MS.

The current criteria allow some people with RIS to be diagnosed with MS if they meet certain conditions. For example, if there is evidence of dissemination in space on an MRI scan, then (if certain other criteria are met) an MS diagnosis might be made even though the person has not had symptoms. This means that some people with RIS will be able to be diagnosed with MS earlier, and be considered for treatment sooner, without having to wait for symptoms to appear.

• What else might it be? (NICE) – information from the National Institute for Health and Care Excellence (NICE) on other conditions that can mimic MS

This information has been developed by the MS Trust Health Information team. Our team produces accurate evidence-based information to help you navigate your every day – working alongside health professionals. We would like to thank Dr Niraj Mistry, Consultant Neurologist, University Hospitals Birmingham NHS Foundation Trust for checking the clinical accuracy of this information.