The McDonald criteria is a tool for clinicians to help them provide an accurate diagnosis of multiple sclerosis (MS) as early as is possible. The criteria provide a guide to the tests required for clinicians to be sure of a formal MS diagnosis.
The McDonald criteria were initially devised in 2001 by a team led by Professor Ian McDonald, and were most recently revised in 2024. This updated version of the criteria was eventually published in 2025.
The criteria are used to seek and establish evidence of damage to the central nervous system (CNS) comprising of the brain, spinal cord and through the 2024 revision, the optic nerve.
Up until the 2024 revision the criteria relied on evidence of CNS damage in two ways
MRI evidence is used in the McDonald criteria extensively and is a requirement for everyone who is diagnosed with MS. Even those with few or no clinical symptoms may show lesions on MRI which may be considered evidence of DIS.
When a lumbar puncture is required, it is oligoclonal bands in the spinal fluid that are looked for. These are a good marker for MS. The bands can show that there has been disease activity in the past which can be used as evidence of DIT.
The DIT and DIS tests help to distinguish MS from other neurological conditions. However, the 2024 revision can mean that for some, MS is diagnosed without evidence of DIT. This may open the door for neurologists to diagnose MS sooner, which could lead to some patients accessing specialist treatment earlier than previously possible.
It is important to note that the 2024 revision of the criteria does not change any previous MS diagnosis. However, those who are still in the diagnosis process, and have been previously diagnosed with clinically isolated syndrome (CIS) or radiologically isolated syndrome (RIS) may wish to speak to their neurologist to discuss how these changes may affect their initial diagnosis.
Below is a table that outlines the 2017 McDonald criteria. After that we will explain more about the 2024 revision and what is means for MS diagnosis.
Click on the image to enlarge the table below.
While the 2017 diagnostic criteria shown in the above table are still relevant, below is a summary of how the new 2024 McDonald Criteria adds more tools to aid a neurologist’s diagnosis.
The 2024 revision now recognises the optic nerve as being a fifth area of the CNS which can be considered when looking for evidence of dissemination in space (DIS). This means that lesions found by MRI within three areas of the brain (periventricular, juxtacortical/cortical, infratentorial) the spine and the optic nerve could be used to underpin DIS. Given that around 25% of people with MS experience optic neuritis as their first MS related symptom, the inclusion of lesions in the optic nerve to support an MS diagnosis is a logical step forward.
The inclusion of CVS as a marker for MS is significant as it helps neurologists to distinguish MS lesions from those which are unrelated to the condition. CVS is the presence of a vein which can look like a line or dot on an MRI scan, that runs through the centre of a lesion. These are very commonly found in MS lesions. While evidence of CVS is not required for MS diagnosis, it can help to speed it up. For example, further evidence of dissemination in time (DIT) for those diagnosed with CIS would not be required if CVS is present in lesions found in at least two of the five CNS locations.
A PRL is a lesion identified via MRI which is distinguishable from other lesions due to having an inactive core surrounded by activated iron-laden microglia. These types of lesions are rarely found in other conditions that present similarly to MS radiologically. Even a single PRL found within the CNS is a strong indicator that a person has MS, however their presence is not required to underpin a formal diagnosis. With the revised criteria, if a patient displays typical MS symptoms, a single PRL is found within one of the five CNS regions, plus evidence of DIT or positive cerebrospinal fluid (CSF) is presented (via lumbar puncture), then a neurologist should have sufficient evidence to diagnose MS.
kFLC are a form of protein which is produced by B-cells and are found within the CSF. If elevated levels of this protein are found, by way of lumbar puncture, then this is an indicator of an inflammatory response within the immune system. This new addition to the criteria can be used in isolation or together with the presence of oligoclonal bands (OCB) found within the spinal fluid, which is the traditional method of evaluating inflammatory reactions indicated with the CSF. However, it is important to note that returning kFLC results can be done quicker in comparison to OCB as it is a fully automated process, while measuring OCB within the CSF requires evaluation by specialist technical staff. This speedier alternative could lead to many people receiving an MS diagnosis sooner than under the 2017 criteria.
For the first time since the criteria was introduced DIT is no longer mandatory for an MS diagnosis. While DIT will still be used as diagnostic criteria in some cases, it will no longer be required for others. This is due to the impact of the other diagnostic indicators that have been introduced. For example, patients initially diagnosed with CIS prior to this revision may have been required to wait and see if further indicators of MS arise in the future before MS could be diagnosed. For example, new lesions appearing and more evidence of symptoms. With the 2024 criteria, more weight is given to DIS, and as such, a person who prior to this revision would initially be given a CIS diagnosis, may be diagnosed with MS if an MRI displays CVS lesions.
If you’d like to learn more about the McDonald criteria, or just MS in general, then get in touch with the MS-UK Helpline today!
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