The McDonald criteria
Specialist doctors called neurologists use the McDonald criteria to diagnose multiple sclerosis (MS).
Neurologists treat conditions that affect the brain, spinal cord and nerves. They use the McDonald criteria to diagnose MS. It’s not easy to diagnose MS. There’s no single test for it. And lots of other things can look like MS. So neurologists need these criteria to help them be sure if someone has MS.
What are the McDonald criteria?
The McDonald criteria are a set of rules neurologists follow when they decide if you have MS. These guidelines were named after the neurologist Professor Ian McDonald. He was a pioneer in MS at the National Hospital for Neurology in London. Neurologists have used these criteria for over twenty years to help diagnose people quicker.
The McDonald criteria change as understanding of MS grows and as tests get better. They’ve been updated several times. Expert neurologists from around the world agree them together.
The latest McDonald criteria
Neurologists now use the latest version of the criteria, called the 2024 McDonald criteria. They were first presented at a conference in that year. Then they were published for all neurologists to use in September 2025.
These latest criteria give neurologists more ways to be sure about an MS diagnosis. Fewer people will be told they have MS when they don’t. And it could make diagnosis quicker and easier for some people.
This latest update doesn’t mean everything in the previous criteria has been overturned. It doesn’t mean a diagnosis with the old criteria was wrong. It just means neurologists have extra guidance when they diagnose people now.
Read our news story about the differences between the old and new McDonald criteria
How do neurologists use the McDonald criteria?
When a neurologist has ruled out other possible causes for your symptoms, they’ll use the McDonald criteria to see if MS is the right diagnosis.
To diagnose MS a neurologist must find evidence of several attacks on your central nervous system that happened at different times. Your central nervous system is your spinal cord and your brain (including the optic nerve which connects to your eye).
Sometimes these attacks cause symptoms, but sometimes they don’t. The neurologist also needs proof that these attacks have affected several places in your central nervous system, not just one.
What kind of evidence do the McDonald criteria need?
When a neurologist uses the McDonald criteria they’re looking for evidence of:
- attacks of MS-like symptoms (also called relapses)
- lesions that are typical of MS. Lesions are signs of scarring or nerve damage in your brain or spinal cord
- results from certain tests
To look for this evidence, the neurologist can use:
- a physical examination
- a history of your symptoms
- tests, including MRI scans and lumbar punctures to check your spinal fluid
Physical examination and your symptoms
The neurologist will look at how your nerves are working. They’ll check your walking and your hand and leg strength. They’ll test your vision, balance, reflexes and coordination. They’ll ask about your history of symptoms. That’s the symptoms you have now and ones you had in the past.
All this tells your neurologist how many attacks (relapses) you’ve had. It also shows what parts of your brain and spinal cord were affected. The type of symptoms you get often depends on where attacks happen in your central nervous system.
MRI scans and other tests
An MRI scan will show if you have lesions in your brain. You can also have scans of your spinal cord or optic nerve if symptoms point to lesions there. Other tests on your optic nerve can include optical coherence tomography (OCT) and visual evoked potential (VEP) tests.
The latest update to the McDonald criteria mentions two new types of lesions that only show up on special types of MRI scans. These are lesions with the central vein sign and paramagnetic rim lesions. If a neurologist sees enough of these on a scan, that can help towards diagnosing someone with MS in some cases.
Testing spinal fluid
During a test called a lumbar puncture, a doctor or nurse puts a thin needle into your lower back. This collects cerebrospinal fluid (CSF). This is the fluid that flows around your brain and spinal cord.
A test then looks for signs of antibodies called oligoclonal bands or high levels of something called kappa free light chains. These are both signs of inflammation in your brain or spinal cord.
Where we talk about what’s needed for an MS diagnosis, when you see ‘a positive test on your cerebrospinal fluid’, we mean the test found oligoclonal bands or high levels of kappa free lights.
These tests aren’t enough on their own to diagnose MS. But they’re an important step towards it. A neurologist can use them instead of looking for other signs that MS has been active over time, not just a one-off event.
‘Dissemination in time and space’
The McDonald criteria usually need evidence of two things to confirm an MS diagnosis:
- ‘dissemination in time’
and
- ‘dissemination in space’
‘Dissemination’ or ‘disseminated’ means ‘spread across’. In MS it describes when and where damage in the brain or spinal cord shows up.
Dissemination in time (DIT)
Dissemination in time means there’s proof that MS has been active on more than one occasion. At different points over time you’ve had new attacks or relapses. Or new lesions have appeared on your MRI scans.
After the 2024 update the McDonald criteria still say, as a general rule, a neurologist needs to see both dissemination in time and space to diagnose MS. But in some cases, dissemination in time is no longer needed if the neurologist can see certain other signs. These are specific lesions or signs in someone’s spinal fluid.
Dissemination in time still plays an important part in diagnosing MS. But if you have lesions in at least four parts of your central nervous system, then it’s not needed.
Dissemination in space (DIS)
Dissemination in space means MS has left signs of scarring or damage at different places within your central nervous system. This shows up as lesions on MRI scans of your spinal cord or your brain (which includes your optic nerve). These lesions don’t always cause symptoms. Dissemination in space is always needed for an MS diagnosis.
What the McDonald criteria ask for in more detail
If your symptoms and lesions are typical of MS, these are the criteria to diagnose MS. If they’re not typical, your neurologist can explain what other things they might take into account.
If you have lesions in at least TWO of the five parts of your central nervous system
You can be diagnosed with MS if you have symptoms and lesions typical of MS in at least two of the five different parts of your central nervous system. This could be in your spinal cord or in four specific parts of your brain, including your optic nerve.
But you also need one or more of these:
- a positive test on your cerebrospinal fluid
- an MRI scan that shows the central vein sign (CVS) in six or more lesions. If you have fewer than ten lesions, more than half must have the CVS
- evidence of dissemination in time (new lesions on MRI scans from different points in time)
- if you have lesions in four or five parts of your central nervous system, you have MS. No need for any further tests or evidence
If you have lesions in only ONE part of your central nervous system
You can be diagnosed with MS if you have symptoms and lesions typical of MS in just one part of your central nervous system. This could be in your spinal cord or in one of the four particular parts of your brain, including your optic nerve.
But you also need one or more of the following:
- a positive test on your cerebrospinal fluid. And you need six or more lesions on your MRI scan with the central vein sign (CVS). If you have fewer than ten lesions, more than half must have the CVS
-
a positive test on your cerebrospinal fluid. And you need at least one paramagnetic rim lesion on your MRI scan
-
evidence of dissemination in time (attacks of symptoms or lesions on MRI scans at different points in time). And you need six or more lesions on your MRI scan with the central vein sign (CVS). If you have fewer than ten lesions, more than half must have the CVS
-
evidence of dissemination in time (attacks of symptoms or lesions on MRI scans at different points in time). And you need at least one paramagnetic rim lesion on your MRI scan
To be diagnosed with primary progressive MS you need:
- progression over at least 12 months. This means your symptoms or disability keep getting worse
- typical MS symptoms and lesions in at least two places in your central nervous system (or two or more lesions on your spinal cord instead)
You must also have one or more of these:
- a positive test on your cerebrospinal fluid
- at least six lesions with the central vein sign (CVS) on MRI scans (or if you have fewer than ten lesions, the majority must have CVS)
- lesions on MRI scans at different points in time (or at least one gadolinium enhancing lesion)
- lesions in four or five parts of your central nervous system (spinal cord or brain, which includes your optic nerve)
For a diagnosis of MS in people over 50 the 2024 McDonald criteria strongly recommend that neurologists find extra evidence. This is also true for people who smoke or have high blood pressure, diabetes, migraine-type headaches or high cholesterol. This also applies if they have vascular disease (problems with their circulation, arteries and veins).
These extra signs can be:
- a lesion on the spinal cord
- a positive test on your cerebrospinal fluid
- MRI scans show six or more lesions with the central vein sign. If you have fewer than ten lesions, more than half must have the CVS
For a diagnosis of MS in people under 18 the 2024 McDonald criteria have some extra guidelines:
- if half of the T2 lesions have the central vein sign, this strongly points to MS. T2 lesions include both old and new lesions
- it’s strongly recommended that children under 12 are tested for a specific type of antibody (myelin oligodendrocyte glycoprotein antibodies). If they have this, they don’t have MS
- this antibody test can be also used with children over 12, but it’s not always needed
- the criteria for diagnosing MS shouldn’t be used with children who have ADEM (acute disseminated encephalomyelitis). This is a one-off inflammation of their central nervous system
Many people who get a diagnosis of CIS will never go on to be diagnosed with MS. For them, it’s a one-off attack of symptoms. But some people with CIS do go on to develop MS.
For a diagnosis of CIS you must have had a one-off attack of symptoms like the ones people with MS get. In most cases an MRI scan will show lesions typical of MS. That scan could be of your spinal cord or your brain (which includes the optic nerve).
You’ll be diagnosed with CIS if neurologists don't have enough evidence to diagnose MS. For example, if there’s a negative test result on your cerebrospinal fluid. These tests look for oligoclonal bands or high levels of kappa free light chains. Or if MRI scans don’t show certain kinds of lesions (paramagnetic rim lesions or ones with the central vein sign).
The 2024 update to the McDonald criteria means fewer people will be diagnosed with CIS. Some people who would have been diagnosed with CIS in the past will now be diagnosed with MS. That could include people whose only symptom is optic neuritis. But only if there’s other kinds of evidence too.
Many people with RIS will never go on to be diagnosed with MS. But for some people it’s an early sign of MS. People with RIS have lesions on their MRI scans but they don’t have symptoms. It’s often picked up when someone has a scan for a reason that has nothing to do with MS.
For a diagnosis of RIS (radiologically isolated syndrome) an MRI scan of your brain or spinal cord must show two or more lesions that are typical of MS. But you must never have had an attack of MS-like symptoms.
Do you still have questions about the McDonald criteria, or anything connected to being diagnosed with MS? You can contact our MS Help Hub, either by phone email, or start a conversation wherever you see the webchat icon.
Last full review: 1 October 2025
Next review date: 1 October 2028
We also update when we know about important changes.
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