New criteria for the diagnosis of MS

At the Annual Neurology Update Meeting 2025, Prof Chris McGuigan, Consultant Neurologist, St Vincent’s University Hospital, Dublin, provided an overview of the newly revised 2024 McDonald diagnostic criteria for multiple sclerosis (MS).

These criteria revise the 2017 version and introduce key updates aimed at improving diagnostic accuracy and consistency across all patient groups, from paediatric to late-onset MS.

 The 2024 McDonald criteria aim to offer a unified diagnostic framework for individuals with relapsing or progressive MS throughout the lifespan.

Prof McGuigan said an MRI of the brain and spinal cord “remains the most useful paraclinical test”. “An abnormal MRI is required to diagnose MS,” he added.

MS diagnosis should be reassessed periodically, according to Prof McGuigan. He also emphasised how misdiagnosis and underdiagnosis may have “deleterious consequences”.

A major change in the new criteria is the inclusion of the optic nerve as a fifth anatomical location within the central nervous system (CNS), in addition to the periventricular, cortical or juxtacortical, infratentorial, and spinal cord regions. This reflects evidence that optic neuritis is a common and early manifestation of MS, detectable by MRI, optical coherence tomography, or visual evoked potentials.

The new criteria also recognise radiologically isolated syndrome (RIS) and certain non-typical neurological symptoms as potential diagnostic pathways when supported by MRI and cerebrospinal fluid (CSF) findings. This approach aims to capture early disease activity and allow earlier initiation of treatment, reducing the risk of long-term disability.

Supportive biomarkers have been expanded to include the central vein sign, paramagnetic rim lesions, and kappa free light chain (kFLC) concentrations in CSF. While not mandatory, these markers can improve diagnostic specificity, particularly in differentiating MS from mimics such as neuromyelitis optica spectrum disorder and myelin oligodendrocyte glycoprotein antibody-associated disease.

Importantly, dissemination in time (DIT) is no longer required as an essential diagnostic criterion. The presence of CSF oligoclonal bands or kFLC positivity can now substitute for DIT, expediting diagnosis without compromising specificity. For patients with typical clinical presentations and MRI findings across four CNS regions, MS can be diagnosed without further delay.

 The 2024 revisions also include guidance for older patients (aged 50 years and above), and those with comorbidities, acknowledging the diagnostic challenges in these groups.

In summary, Prof McGuigan said that “MS remains a disease of exclusion”.

“The 2024 revisions to the McDonald criteria, now published, should be used for diagnosing MS,” he told the meeting.

The criteria acknowledge the presymptomatic phase of MS and also introduce novel imaging techniques to aid diagnosis in certain circumstances.

Overall, the new criteria “allow for earlier diagnosis and, therefore, the initiation of therapy if appropriate”, according to Prof McGuigan.