For this year’s MS Awareness Month, we have chosen to focus on how the revised McDonald Criteria are being implemented in clinical practice worldwide.
What has been the major change brought by the 2024 revisions in clinical practice? We asked Dr Wallace Brownlee, of University College London Hospitals.
“The big change in my practice has been knowing that dissemination in time is no longer necessary. Unlike some of the other updates, which rely on implementation of new diagnostic tools, this change has had immediate impact. Every person we see with suspected multiple sclerosis (MS) undergoes magnetic resonance imaging (MRI). With a single, non-contrast MRI scan of the brain and spinal cord, we can now diagnose approximately a quarter to a third of patients without the need for a follow-up scan, contrast-enhanced imaging or a lumbar puncture. I think this is emerging as an efficient way to establish new MS diagnoses.”
The median time to MS diagnosis is 40 days using the 2024 McDonald Criteria, compared with 84 days under the 2017 criteria, in a study involving 274 individuals. Furthermore, more diagnoses are established after the initial diagnostic workup with the revised criteria (220 cases) than with the previous version (172 cases) [1.] The performance is similar in children and older adults.
Availability and Routine Use of Paraclinical Tests
What are the global challenges to MS diagnosis? Professor Andrew Solomon – from University of Vermont – tells us: “A couple of years after the publication of the 2017 revisions, the MS International Federation (MSIF) and its country coordinators assessed the state of MS care across 107 countries [2.]. In 2019, 88% of countries reported using the 2017 revisions. However, many older diagnostic criteria were still commonly applied. In some countries, even the Poser criteria continued to be used.
In fact, in 20 countries the most used MS diagnostic criteria were not the 2017 revisions. This represented a problem. Why were the updated criteria not used in all countries? Primarily due to a lack of awareness and training [2.]. Importantly, this issue was not confined to low- or lower-middle-income countries. For the 2024 revisions, however, I believe that there are more concerted efforts toward implementation.
Three companion papers addressing the assessment of the visual pathway, cerebrospinal fluid (CSF), and MRI are now available and provide clearer guidance on how to apply the criteria. These resources offer additional tools to explain the rational for changes and to facilitate implementation. Moreover, on behalf of the committee, a tremendous number of speaking engagements have taken place around the world – many of which are still ongoing – aimed at helping clinicians learn how to use the criteria. In parallel, educational initiatives are underway, including online training modules. These efforts are expected to make the criteria more accessible.”
The introduction of cutting-edge paraclinical tools in the 2024 revisions determines a shift in clinical practice and introduces new technical challenges [4.]. It will require time and additional training before centres worldwide can routinely assess and use these tools effectively [4.]. However, the improved sensitivity and specificity offered by the updated criteria are certainly worth the effort [4.].
At ECTRIMS 2025, Professor Solomon presented the results of a survey conducted with the MSIF to assess the availability and routine use of paraclinical tests in 122 countries with 82% responses. He explains the results to us, “Overall, the main message is that MRI is widely available and routinely used, although with certain caveats. The availability of tests such as optical coherence tomography (OCT) and kappa free light chains is also encouraging – approximately 50% of countries report access to kappa free light chain and nearly 90% report availability of OCT.
However, these tests were not routinely used at the time of the survey in many countries. Even oligoclonal band testing is not routinely used in more than one third of countries, partly due to barriers to accessing CSF testing and the expertise required to perform and interpret this test. Moreover, most of these paraclinical tools were significantly less available in lower- and lower-middle-income countries.
This highlights both opportunities and disparities in access to paraclinical testing across regions. Continued advocacy will be necessary to make all these tests available. Importantly, we now have multiple diagnostic pathways, and alternatives can often be used when specific tests are not accessible. The flexibility of the criteria is expected to improve access to MS diagnosis.”
Getting to Grips with Multiple Diagnostic Pathways
Multiple diagnostic pathways may represent both an opportunity and a challenge. How does this translate into the real-world clinical practice?
“I think the first challenge is getting to grips with the greater complexity of the new criteria,” says Dr Brownlee, “We are working in our centre to improve access to OCT scanning. People with acute optic neuritis are often evaluated with MRI and OCT. However, for people presenting without optic neuritis, routine assessment of the optic nerve is currently not routine. Access to these paraclinical tools and experience in interpreting them will need to build over time. We have only been using the criteria for a few months. The next important step will be validating them in real-world settings and understanding the challenges or potential pitfalls of applying them in everyday clinical practice. At present, much of the evidence underpinning the criteria comes from research-based cohorts, which do not always reflect the types of patients we regularly see in the clinic. Real-world validation of the criteria will be essential.”
The Radiologically Isolated Syndrome
The 2024 revisions have also expanded the MS clinical spectrum to incorporate radiologically isolated syndrome (RIS) in certain situations [3.]. RIS lies within the MS continuum [5.], and it is characterised by the incidental observation of white matter lesions in the central nervous system that are highly typical of MS but occur in the absence of clinical symptoms of inflammatory demyelination [6.].
We discuss the RIS criteria with Professor Christine Lebrun-Frénay of the University of Nice, co-founder in 2009 of the RIS Consortium. “To facilitate the application of the RIS diagnostic criteria worldwide and reduce the risk of misdiagnosis, we decided that individuals with RIS or who experienced atypical symptoms should have at least one MRI lesion in two anatomical regions and at least one additional feature among dissemination in time, CVS, or positive CSF. In the absence of symptoms, in individuals over 50 years, or at any age in the presence of comorbidities, two of these criteria are recommended to minimise the risk of misdiagnosis of the T2 lesion origin.”
To date, 44 countries participate in the RIS Consortium with more than 200 MS-specific centres and a database of over 2500 individuals with RIS. “We hope that many other countries will join us in improving our knowledge of the preclinical phase of MS to validate the new criteria in the real world,” concludes Professor Lebrun-Frénay.
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Written by Stefania de Vito
Special thanks to Professor Christine Lebrun-Frénay (University of Nice, CHU de Nice), Professor Andrew Solomon (University of Vermont), and Dr Wallace Brownlee (University College London Hospitals NHS Foundation Trust) for their insights.
References
[1] Brownlee W.J. et al. Neurology 2026; 106(6): e214688.
[2] Solomon A.J. et al. Neurology 2023; 101(6): e624-e635.
[3] Leeuwenberg K. E. et al. BMC Neurology 2026.
[4] Fox RJ & Jones SE Lancet Neurol. 2025; 24(10): 808-810.
[5] Montalban X. et al. Lancet Neurol. 2026; 24(10): 850-865.
[6] Lebrun-Frénay C. et al. Brain 2023; 146(8): 3431-3443.