The accumulation of evidence indicating that earlier treatment can lead to better long term outcomes for people with MS has highlighted the importance of early diagnosis. However, early diagnosis should be approached with caution to ensure the correct diagnosis is made and to avoid misdiagnosis and inappropriate treatment of people who do not have MS.

In 2001, MS diagnosis was standardised with the establishment of the McDonald criteria. These criteria help clinicians to rapidly identify MS and rule out other conditions. The criteria have been revisited a number of times since 2001 and the 2017 revision has now been published in The Lancet Neurology. This is the first formal publication of revisions to the criteria since they were initially published.

The update to the McDonald diagnostic criteria was undertaken by an international panel of expert MS neurologists. They reviewed the existing criteria and the latest scientific advancements in our understanding of MS, along with improvements in the technology used to diagnose MS. This update does not significantly change the way that MS is diagnosed; rather, it refines certain aspects of the criteria and incorporates the latest evidence on lesion locations that help make the diagnosis of MS as early and as accurately as possible, whilst reducing the risk of misdiagnosis.

There is still no single clinical feature or test that can definitively provide a diagnosis of MS, and the panel emphasise that the diagnosis of MS requires the careful integration of clinical information, imaging scans, and laboratory tests.

A diagnosis of clinically definite MS relies on the concept of ‘dissemination in space and time’. This means that there must be evidence for multiple ‘attacks’ and/or MRI lesions in the brain that are physically distributed (disseminated) in different locations in the brain and spinal cord, as well as evidence of new lesions occurring over time.

Clearer guidelines

The revised criteria provide clearer guidelines on the number and locations of lesions that can provide evidence for dissemination in space and time. Lesions in the brainstem or spinal cord that cause MS symptoms (symptomatic), as well as lesions not linked to symptoms (asymptomatic), can now be included. Though harder to detect in conventional MRI scans, lesions in the cortex, the outer grey matter of the brain, can also provide evidence for dissemination in space.

The revised criteria also revitalise the role of cerebrospinal fluid (CSF) analysis in diagnosing MS. In MS, it is very common to find antibodies in the CSF which show up as a characteristic banding pattern known as oligoclonal bands. With the widespread use of MRI scans in the diagnosis of MS, CSF analysis (also known as a spinal tap) has become less common. With the 2017 revisions, oligoclonal bands can substitute for lesions to demonstrate dissemination in time in a person with the potential precursor to MS, known as clinically isolated syndrome (CIS), and who also meets the MRI criteria for dissemination in space.

While oligoclonal bands are not unique to MS, they can support the diagnosis if clinical and MRI diagnostic features are not clear-cut. Equally, the absence of oligoclonal bands does not rule out MS, but other CSF findings, such as increased protein concentration or the presence of certain cells, can suggest other diseases.

Different populations

As the original McDonald criteria were based largely on evidence from adult European and North American populations, the panel also reviewed the use of the criteria in different populations. They concluded that there was no evidence that the McDonald criteria cannot be applied in children or in Asian, Middle Eastern, Latin American and African populations. However, they urged particular vigilance to rule out related neuromyelitis optica spectrum disorders, which can be more common in some of these populations.

These 2017 revisions to the McDonald criteria go a long way towards helping to achieve the much needed balance between rapid MS diagnosis and avoidance of misdiagnosis. The panel also reviewed the emerging evidence on further diagnostic tools that, in future revisions, will undoubtedly continue to improve diagnosis and reduce the long-term impact for people with MS.

With thanks to MS Research Australia – the lead provider of research summaries on our website.