Understanding the updated McDonald criteria for diagnosing MS

Diagnostic criteria are guidelines used by clinicians to help make an accurate and early diagnosis of a disease. They encompass a specific combination of signs, symptoms and test results. The diagnostic criteria for MS have evolved over time as the understanding of the disease has improved. 

The current diagnostic criteria for MS are known as ‘McDonald criteria’ after Professor Ian McDonald who led their development in 2001.  Since then, the McDonald criteria have been updated several times. Now, the 2024 revisions – which were agreed by an international group of MS experts – build on the existing criteria, introducing new tools, markers, and pathways to speed up MS diagnosis and improve accuracy. The revised McDonald diagnostic criteria were recently updated and published in The Lancet journal. 

‘The 2024 McDonald criteria are an important step forward for the global MS movement. They bring us closer to timely and accurate diagnosis, which opens the door to effective treatment and better quality of life. To make this progress real, the criteria must be adopted in every country and supported with the right training, equipment and resources. This is especially vital in low- and middle-income countries, where access to diagnostic tools is often limited. For people with MS everywhere, the revisions offer a clearer and faster path to diagnosis, giving them the chance to begin treatment sooner and move forward with greater certainty.’

Dr Lydia Makaroff, Chief Executive, MS International Federation

What’s new in 2024? 

 The 2024 updates include changes to where and how we look for evidence of MS, expanding the ways MS can be diagnosed and including new tests in the diagnosis process. These additions have been made whilst maintaining the core criteria from the previous versions.  

• Faster diagnosis: The requirement for ‘dissemination over time’ (meaning there is evidence of a relapse or specific symptoms occurring at more than one time point) has been removed, enabling some people to receive an MS diagnosis without waiting months or years for a second relapse or attack of symptoms. 

• Expanded diagnostic evidence: Previously, there had to be evidence of nerve damage in two out of four areas of the brain and spinal cord to demonstrate ‘dissemination over time’. Now, it’s possible to include damage to a fifth area, the optic nerve, as well. This opens opportunities for collaboration with ophthalmologists and the use of optical coherence tomography (OCT) or visual evoked potential tests, if available. 

• Radiologically Isolated Syndrome (RIS): People with evidence on an MRI scan of nerve damage in the central nervous system (CNS) — even without the usual clinical symptoms of MS — may now meet the criteria for MS if other factors are met. Previously, these individuals would have had to wait until symptoms of MS developed to be diagnosed; the new criteria provide the opportunity for earlier diagnosis, treatment and monitoring. 

• Specialised guidance: The criteria contain new considerations for diagnosing children and people over 50, recognising that MS can be harder to distinguish from other conditions in these age groups. 

‘The updated 2024 McDonald criteria will help clinicians to diagnose MS – whether it occurs in children, young adults or older people – with greater speed and accuracy. This allows people to start taking the right disease-modifying therapies as soon as possible, leading to better outcomes. It is essential for the MS community to work together to help everyone across the world benefit from these advances.’

Professor Brenda Banwell, Chair of MSIF’s International Medical and Scientific Board. 

What do the 2024 criteria updates mean for me?  

The 2024 updates will have a different impact depending on whether you are already diagnosed, are awaiting diagnosis, or are working to improve MS healthcare in your country. 

I’m already diagnosed with MS

For most people who have MS, the new criteria will not change your existing diagnosis. However: 

• If your diagnosis was uncertain or under review, you may find that the new criteria help confirm (or rule out) MS more quickly. 

• You may wish to discuss the changes with your neurologist if you have questions about your diagnostic journey. 

• If you worry about family members or friends developing MS, the path to diagnosis — if needed — could be faster and more precise. 

I’m not yet diagnosed with MS but am experiencing symptoms

The revised criteria are designed to shorten the often stressful and uncertain wait for diagnosis: 

• The removal of the ‘dissemination over time’ requirement means that a diagnosis can sometimes be made after a single relapse or symptom occurrence if other evidence is present. 

• Inclusion of the optic nerve as a diagnostic region broadens the range of evidence that can be used by clinicians to make the diagnosis.  

• If you have been diagnosed with RIS, there are now clear steps for making a diagnosis of MS, which could lead to earlier monitoring and treatment. 

I’m a healthcare professional

The 2024 revision of the McDonald criteria introduce changes to the diagnostic approach that can impact clinical practice. Familiarise yourselves with the updated McDonald Criteria guidelines for a more unified approach to diagnosing MS, including new tests for diagnosis as well as specialised criteria for diagnosing children and people over 50. You can learn more on the ECTRIMS website.

I’m a member of an MS organisation 

The potential benefits of the revised criteria will only be experienced by people if healthcare systems adopt the new criteria and can provide access to the necessary diagnostic tools. MS organisations have a crucial role in raising awareness of the 2024 diagnostic criteria and advocating for them to be incorporated in national guidelines. In countries with limited access to OCT or visual evoked potentials, the changes strengthen the case for advocacy to expand these services too. MS organisations should aim to:  

• Communicate: Share clear, accessible explanations with neurologists (especially those who are not specialised in MS), ophthalmologists, and allied health professionals. 

• Train: Working in partnership with professional organisations (e.g. neurology academies), facilitate training and awareness sessions to build confidence in applying the criteria. 

• Advocate: Push for inclusion of the criteria in national guidelines and for improved access to diagnostic tools, particularly MRI, OCT and KFLCs. 

• Support implementation: Work with healthcare systems and professional bodies to reduce barriers to adoption, including addressing misconceptions and resource constraints. 

How were the criteria updated? 

Our member organisation in the USA, the National MS Society, together with the European Committee for Treatment and Research in MS (ECTRIMS) sponsored an international committee that was set the task of reviewing and updating the previous 2017 McDonald diagnostic criteria. This committee was made up of 56 experts from 16 countries – all with expertise in clinical management, radiology, methodology, epidemiology and patient perspectives. MSIF was represented on the committee by Professor Brenda Banwell and Professor Jorge Correale, the Chair and Deputy Chair of MSIF’s International Medical and Scientific Board. 

The peer-reviewed paper that describes the updated criteria in detail, titled ‘Diagnosis of multiple sclerosis 2024 revisions of the McDonald criteria was published in the October issue of Lancet Neurology, and online on 17 September.  

Two supporting papers published in the same issue include:  

• Imaging Guidelines: ‘2024 MAGNIMS-CMSC-NAIMS consensus recommendations on the use of MRI for the diagnosis of multiple sclerosis’  

• Visual System: ‘Recommendations on the use of optical coherence tomography and visual evoked potentials for fulfilling dissemination in space as part of the 2024 Revised McDonald diagnostic criteria for multiple sclerosis’  

Improving diagnosis globally 

Barriers to implementing the updated criteria are not limited to resource-poor settings. In a previous Atlas of MS survey, even high- and upper-middle-income countries reported obstacles to adopting the 2017 criteria, ranging from lack of awareness to gaps in training. This highlights the importance of coordinated communication, professional education, and advocacy to ensure the 2024 updates translate into faster and fairer diagnoses around the world. 

By taking action now, MS organisations will help ensure that these advances are implemented to bring about benefits for people affected by MS — wherever they live. 

Glossary 

MRI: Magnetic Resonance Imaging: A medical imaging technique that uses strong magnetic fields and radio waves to create highly detailed pictures of the inside of the body, including the brain and spinal cord.

KFLCs: Kappa Free Light Chains: A type of protein produced by specialised immune cells called plasma cells. Elevated levels found through a blood test can indicate immune cell disorders.  

DIT: Dissemination in Time: Evidence that multiple sclerosis (MS) lesions have appeared at different points over time, indicating the disease is progressing and affecting multiple areas of the central nervous system, as confirmed by MRI scans or clinical relapses. 

DIS: Dissemination in Space: A criterion that indicates that inflammation has occurred in multiple areas of the central nervous system 

RIS: Radiologically Isolated Syndrome: A condition where a person has brain or spinal cord lesions that look like multiple sclerosis (that might be picked up on an MRI scan taking place for a different reason, such as migraine) but has no MS symptoms.  

OCT: Optical Coherence Tomography: A non-invasive imaging technique that creates 3D images of the eye to help diagnose and treat eye conditions. 

CNS: Central Nervous System: The brain and spinal cord.