Dr. Jiwon Oh, Director of the BARLO MS Centre and the Waugh Family Chair in Multiple Sclerosis Research at St. Michael’s Hospital

The international guidelines for diagnosing multiple sclerosis (MS), called the McDonald criteria, underwent their most significant overhaul in a decade in 2024. The internationally recognized framework is used to diagnose MS by combining clinical, imaging and laboratory findings. Dr. Jiwon Oh, Director of the BARLO MS Centre and the Waugh Family Chair in Multiple Sclerosis Research at St. Michael’s Hospital, was among the experts who helped to write them.

Now, in a commentary published in Nature Medicine, Dr. Oh has brought together nearly 30 of the world’s leading MS clinicians to critically evaluate what those changes mean and where the field must go next to improve health outcomes for people with MS.  Many of its co-authors also helped develop the revised criteria in 2024.

“This commentary looks critically at the new criteria and explains why these changes matter, what challenges may arise as they’re used, and what can be done to address them,” explains Dr. Oh. “It also takes a broader look at where the field needs to go next.”

What changed in 2024 and why it matters

For decades, MS diagnosis rested on patient symptoms and neurological exams. But as scientific tools have advanced, diagnosis increasingly relies on biological markers. With measurable signs of the disease detected through imaging and lab tests, MS can be detected earlier than ever before.

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The 2024 MS diagnostic criteria changes reflect a shift in how MS itself is understood. Rather than viewing the disease as a set of distinct subtypes, the commentary says that there is a growing recognition that MS is a single spectrum, in which relapses and progression stem from distinct disease biologies that are both active in most people with MS all along. The revised criteria are meant to reflect that thinking, offering a single framework for diagnosing MS regardless of the patient’s age or how the disease presents.

The authors of the commentary describe this revision as a substantial departure from earlier versions, showing how MS can be caught earlier now, before symptoms appear.

Among the key changes are new tools and the possibility of diagnosing MS even before typical symptoms arise:

  • The optic nerve, which carries signals from the eye to the brain, was added as a key place for clinicians to check for MS.
  • Patients and clinicians must no longer wait for typical symptoms or multiple flare-ups to get a diagnosis. In the past, confirming MS required patients to wait for multiple incidents of flare-ups over a period of time to get a diagnosis.
  • Newer scans can now confirm MS more precisely, revealing markers that can distinguish it from other conditions that have historically mimicked MS.
  • A newer, more widely available spinal fluid test can now help confirm MS, giving doctors an easier option than before.

The challenges ahead

Dr. Oh and the co-authors of the commentary note that the changes are designed to catch MS earlier, but warn that loosening up some criteria for diagnosis can raise the risk of misdiagnosis and overdiagnosis.

Dr. Oh says, “The criteria have built-in safeguards against this, including ensuring that MRI scans are used to confirm the disease whenever possible, using new MRI tools that are very specific for MS, and there are also extra checks for groups where misdiagnosis is more likely, like children and older adults.”

The authors also stress an important distinction that a diagnosis is not the same as a prescription. Not everyone diagnosed under the new criteria will need to begin treatment right away, and patients should be fully informed and involved in decisions about their care, especially those who don’t yet have symptoms.

Access across the world, including Canada, remains a challenge too. Some of the newer tools and specialized scans, including specialized MRI scans that can detect the imaging markers of MS, rely on equipment and expertise not available everywhere.

What’s next

The commentary lays out the work still ahead. That includes developing better tools to predict how a person’s disease will progress and to monitor it over time. The authors also call for a clearer way to describe the course of the disease, and for clinical trials to be redesigned so new treatments can reach patients faster.

“The 2024 revisions were the biggest change ever made to the most fundamental criteria in our field, all aimed at improving outcomes for people with MS,” says Dr. Oh. “But major changes bring challenges, and there’s still a lot of work ahead.”

The greatest unmet need they identify is effective treatments for the mechanisms that drive long-term disability that is independent of relapsing biology. In a separate review recently published in Lancet Neurology, led by Dr. Oh, she describes the promise of a new class of drugs called Bruton tyrosine Kinase (BTK) inhibitors that may be able to target the chronic immune system activity compartmentalized within the central nervous system underlying disability progression that is independent of relapsing biology, offering what current treatments aren’t effectively addressing.

About the author

The commentary was led by Dr. Jiwon Oh, Director of the BARLO MS Centre at St. Michael’s Hospital, the Waugh Family Chair in Multiple Sclerosis Research, and a co-author and Steering Committee member of the 2024 McDonald criteria. She brought together nearly 30 of the world’s leading MS clinicians and scientists, many of whom helped write the revised criteria, assessing what the changes mean and where the field should go next.

About the BARLO MS Centre

The BARLO Multiple Sclerosis (MS) Centre at St. Michael’s Hospital is one of the largest of its kind in North America. Our world-class clinician-scientists are working to revolutionize the understanding and treatment of MS.

To learn more about the clinic and MS, please visit the BARLO MS Centre website. 

By Zehra Goawala

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