The set of guidelines used by neurologists to diagnose MS, known as the McDonald criteria, has recently been updated to reflect the latest research and our better understanding of MS.
The McDonald criteria were last updated in 2017. The new revisions (finalised in 2024 and published in September 2025) widen the evidence that can be used to diagnose MS and include new guidance on diagnostic markers that can identify MS more accurately.
The 2024 criteria also provide a more unified approach for diagnosing relapsing and progressive disease courses in children through to older people. This signals a move towards thinking of MS as a single condition with similar biological changes, rather than as three separate types.
The changes to the McDonald criteria are likely to speed up diagnosis, make MS easier to diagnose, and reduce the chance of MS being diagnosed incorrectly.
Some of the key changes are listed below.
- Optic nerve damage can be used as evidence of MS.
- Dissemination in time (MS damage occurring at different points in time) is no longer considered essential for diagnosis in certain situations.
- New diagnostic markers can be used to support a diagnosis (central vein sign, paramagnetic rim lesions and kappa free-light chains).
- People with clinically isolated syndrome (CIS) or radiologically isolated syndrome (RIS) may be able to receive an MS diagnosis earlier.
- Additional guidance for diagnosing MS in children, older people and those who are more at risk of conditions affecting the blood vessels means there’s less chance of MS being misdiagnosed.
If you’d like to read about these changes in more detail, please see our A–Z on the McDonald criteria.
If you’ve already been diagnosed with MS, the changes to the diagnostic criteria won’t affect your diagnosis.
If you’re currently going through investigations for MS, your neurologist may be able to confirm (or rule out) MS more quickly.
If you’ve been diagnosed with clinically isolated syndrome (CIS) or radiologically isolated syndrome (RIS), you may want to speak to your neurologist about what the updated criteria means for you and if it may change your diagnosis.
The 2024 McDonald criteria widen the range of evidence that can be used to make an MS diagnosis. This means that people experiencing neurological symptoms are likely to be diagnosed with MS earlier, start treatment faster and have better outcomes in the future.
