Your diagnosis of multiple sclerosis may have been made using the McDonald criteria. This is a tool for neurologists to ensure that they provide an accurate diagnosis of MS as early as possible, and guide them to the tests they should arrange for you in order to be sure.
The first set of criteria were published in 2001 by a team led by Prof Ian McDonald. They have been extensively revised several times. The revisions are made by a panel of MS experts who look at the most up-to-date research on how MS appears and progresses in patients.
The McDonald criteria were revised 2017 and more recently in 2024. The 2024 criteria take into account recent advances in imaging and research. They were published in September 2025.
Diagnosing MS can be difficult, as the initial symptoms are varied and can be hard to distinguish from other conditions. Over the years, researchers have been looking for ways to confidently identify MS as early as possible. Early diagnosis and treatment has been shown to lead to better outcomes for people with MS, such as slower progression and less severe disability.
To give a diagnosis of MS, the neurologist is looking for evidence of damage to the central nervous system that is disseminated (spread out) in time and space. This means showing that damage has occurred at different dates (dissemination in time, or DIT) and to different parts (dissemination in space, or DIS) of the brain and/or spinal cord. This generally distinguishes MS from other similar neurological conditions.
Neurologists can use a range of evidence sources, including a neurological examination, MRI scans, samples from a lumbar puncture or measures of nerve conductance (evoked potentials tests). Your personal history of symptoms is an important part of the evidence too.
A diagnosis of MS is most secure if there is more than one kind of evidence. Misdiagnosing MS could put patients at risk from unnecessary side-effects of MS drugs.
Dissemination in Time (DIT)
To find evidence of DIT, the neurologist is looking for signs that you have had more than one episode of inflammation around your central nervous system. This could be a relapse, an MRI scan that shows new lesions compared to an older scan, or a lumbar puncture sample that shows you have had inflammation in the past (oligoclonal bands).
Dissemination in Space (DIS)
To find evidence of DIS, the neurologist is looking for signs that inflammation has happened in more than one place in your central nervous system. This could be shown if you have had symptoms that affect different parts of your body, or you have an MRI scan that shows lesions in different places in your central nervous system. Neurologists define areas in your central nervous system in a way that means closely linked areas (topologies) count as one place.
The five areas where neurologists focus are the spinal cord, around the lateral ventricles or spaces in the centre of the brain (periventricular), in or touching the outermost brain layer or cortex (cortico-juxtacortical), around the brainstem or base of your brain (infratentorial), and the optic nerve (the nerve at the back of each eye that sends messages to the brain).
When you visit your neurologist for the first time, they will listen to your account of your symptoms including how and when you experienced them. Using the McDonald criteria, the neurologist can assess what additional evidence they need to collect to make a robust diagnosis of MS.
So, if you have a neurological symptom that suggests a potential first MS event (CIS), your neurologist may ask you to have an MRI scan and lumbar puncture. If these tests show lesions in the central nervous system and oligoclonal bands in your spinal fluid, a diagnosis of MS could be made immediately. You would not need to wait for another attack or relapse before starting treatment.
The table below shows the 2017 McDonald criteria. In the left column is the information that the neurologist already has, and in the right column is the additional evidence they need to collect.
The McDonald criteria have recently been updated to reflect the latest research and our better understanding of MS.
The McDonald criteria were last updated in 2017. The new revisions (finalised in 2024 and published in September 2025) widen the evidence that can be used to diagnose MS and include new guidance on diagnostic markers that can identify MS more accurately. These changes are likely to make MS quicker and easier to diagnose, help get people on treatment earlier so they have better outcomes, and reduce the chance of MS being diagnosed incorrectly.
The 2024 criteria also provide a more unified approach for diagnosing relapsing and progressive disease courses in children through to older people. This signals a move towards thinking of MS as a single condition with similar biological changes, rather than as three separate types.
Optic nerve damage can be used as evidence of MS
To make a diagnosis of MS, neurologists must find evidence that MS damage (lesions) has occurred in more than one area in the brain and spinal cord (central nervous system). This demonstrates what’s known as ‘dissemination in space’. The four areas they currently focus on are:
- around the spaces in centre of the brain (periventricular)
- in or touching the outermost brain layer or cortex (cortico-juxtacortical)
- around the brainstem or base of your brain (infratentorial)
- the spinal cord.
In the updated diagnostic criteria, the optic nerve (the nerve at the back of each eye that sends messages to the brain) has been added as a fifth area that can be used to show evidence of dissemination in space.
Damage to the optic nerve can be found through an MRI, visual evoked potentials (VEP) and optical coherence tomography (OMT).
Dissemination in time no longer considered essential
Previously, to make a diagnosis, neurologists had to find evidence that MS damage had occurred at different points in time (not all at once). This demonstrates what’s known as ‘dissemination in time’.
In the updated criteria, there are certain situations where evidence of dissemination in time is no longer needed to make an MS diagnosis. For example, if you have lesions in four or five of the areas listed above, you can be diagnosed with MS right away, without having to wait for more disease activity.
Central vein sign can be used to confirm diagnosis
MS lesions often have a blood vessel running through the middle which can be seen on MRI scans. This is known as the central vein sign (CVS) and can be used as a diagnostic marker of MS.
In the updated criteria, the presence of CVS can be used to help make an MS diagnosis in certain situations.
For example, if lesions have been found in two or three areas in your brain and spinal cord, and the central vein sign can be identified on MRI, then a diagnosis of MS can be made. You’d no longer have to wait for further MS activity to happen at a later point in time. This may help people with clinically isolated syndrome (CIS) receive an MS diagnosis quicker.
Paramagnetic rim lesions can be used to confirm diagnosis
Some active MS lesions have a distinctive dark rim around the edge. These are known as paramagnetic rim lesions (PRLs) and can be detected by MRI.
In the updated criteria, if PRLs are found on an MRI scan, this can be used to confirm an MS diagnosis in certain situations.
Kappa free-light chains can be used in place of oligoclonal bands
Kappa free-light chains are molecules that are produced by white blood cells, as part of the immune response. They can be detected in the spinal fluid taken from a lumbar puncture. They’re a sign of inflammation. Researchers have compared them to oligoclonal bands and have shown that they are just as accurate in identifying MS.
In the updated criteria, kappa free-light chains can be used instead of oligoclonal bands when diagnosing MS.
Clearer path to diagnosis for those with radiologically isolated syndrome
Sometimes people may have an MRI scan or lumbar puncture for other reasons (e.g. trauma or migraine) but it shows up damage that is characteristic of MS. Previously, where this happened, people were given a diagnosis of radiologically isolated syndrome (RIS) and had to wait for symptoms to appear before they could be diagnosed with MS.
Neurologists can now diagnose MS in people with no symptoms if they meet certain criteria. For example, if the neurologist has evidence of dissemination in space and time from an MRI scan, an MS diagnosis can be made despite the person experiencing no symptoms.
This means people with RIS can be diagnosed with MS earlier and start treatment sooner.
Less chance of misdiagnosis in children and older people
The 2024 updates include additional guidance on diagnosing MS more accurately in children, older people and in 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 more guidance on differentiating MS from other conditions through certain tests. As well as this, if 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 people and those with vascular risk factors, additional evidence may be needed to make an MS diagnosis. In particular:
- a spinal cord lesion
- signs of inflammation in the spinal fluid
- presence of central vein sign.
If you’ve already been diagnosed with MS, the changes to the diagnostic criteria won’t affect your diagnosis.
If you’re currently going through investigations for MS, your neurologist may be able to confirm (or rule out) MS more quickly.
If you’ve been diagnosed with clinically isolated syndrome (CIS) or radiologically isolated syndrome (RIS), you may want to speak to your neurologist about what the updated criteria means for you and if it may change your diagnosis.
