Christina Applegate recently shared that she had been misdiagnosed with multiple sclerosis (MS). She’s now looking for answers about symptoms that remain unexplained.
With MS misdiagnosis receiving increased attention, it is important to keep the issue in perspective. Neurologist Prof Todd Hardy, a Clinical Professor in Medicine at the University of Sydney, emphasises that most people diagnosed with MS are correctly diagnosed.
With that broader picture in mind, we explore how MS is diagnosed, why misdiagnosis can occur and what is being done to help people get accurate answers and appropriate care and support.
Why diagnosis takes careful assessment
Diagnosing MS involves looking at how symptoms, scans and other test results fit together. Prof Hardy says this can be difficult because there is no single test that definitively establishes the diagnosis.
“Neurologists rely on a combination of clinical symptoms, MRI findings and, in some cases, investigations such as cerebrospinal fluid analysis.”
Cerebrospinal fluid is the fluid surrounding the brain and spinal cord. Prof Hardy also explains that other neurological conditions can produce similar symptoms and scan results, making careful interpretation essential.
“Making an accurate diagnosis requires careful clinical judgement, consideration of alternative explanations and, importantly, ensuring that the findings meet established diagnostic criteria.”
Understanding the figures on misdiagnosis
Christina Applegate’s experience has raised questions about how often MS is misdiagnosed and why it happens. Prof Hardy points to research from specialist centres:
“Studies suggest that a meaningful proportion of people (perhaps as high as 15%) referred to specialist centres with a diagnosis of MS may ultimately be found not to have the disease,” Prof Hardy says.
Importantly, this figure relates specifically to people referred to specialist centres and does not represent the rate of MS misdiagnosis across Australia.
Prof Hardy says misdiagnosis can occur for several reasons, including how symptoms and MRI findings are interpreted:
“Misdiagnosis can occur when non-specific changes on an MRI are interpreted as MS, when symptoms are attributed to MS without sufficient supporting evidence, or when alternative diagnoses are not adequately considered. The key is to look at the whole clinical picture and apply the diagnostic criteria carefully.”
Progress in diagnosing MS
Research is giving neurologists more tools to diagnose MS earlier and more accurately. In September 2025, updated international guidelines, known as the 2024 McDonald criteria, were published. They guide neurologists in deciding whether there is enough evidence for an MS diagnosis.
In some circumstances, the revised criteria allow an MS diagnosis without waiting for another episode of symptoms, helping people access appropriate treatment sooner.
One change involves the optic nerve, which connects the eye to the brain. Evidence of MS-related damage to this nerve can now count towards a diagnosis, with specialised eye scans helping identify that damage.
The updates also recognise MRI patterns more characteristic of MS, helping neurologists assess whether changes reflect MS or another condition. Testing for proteins called kappa free light chains in the fluid surrounding the brain and spinal cord offers another source of supporting evidence.
These tools still need to be considered together. Careful clinical judgement remains essential, including checking whether another condition better explains the findings.
The impact of a changed diagnosis
For someone who has been planning their life around an MS diagnosis, learning that it was incorrect can mean reconsidering decisions about their future while still seeking answers about their symptoms.
“This is particularly concerning because MS is a lifelong diagnosis that can have profound implications for a person’s treatment, future planning and sense of identity,” Prof Hardy says.
A changed diagnosis also means working with their treating team to understand what is causing their symptoms and what treatment and support they need.
“An incorrect diagnosis can cause years of anxiety, uncertainty and fear about disability, as well as exposing people to unnecessary investigations and potentially inappropriate treatments, which can carry significant risks. Equally concerning, the real cause of their symptoms may go undiagnosed or untreated.”
Improving the diagnosis journey in Australia
As diagnostic tools improve, we also have an opportunity to improve the experience of getting a diagnosis. That starts with recognising symptoms and helping people find the right care, then continues with support after a diagnosis is made.
Our My Diagnosis report draws on lived experience and research to identify where Government investment could make a difference:
- Research to help detect MS earlier. A National MS Biobank would bring together biological samples, such as blood, with clinical, genetic and scan information to help researchers identify reliable signs of early MS.
- Education for health professionals. Better understanding of neurological conditions can help health professionals recognise symptoms and support people through the diagnosis process.
- Support after diagnosis. MS Australia is also calling for better access to MS nurses, who provide education, advice, care and ongoing support for people living with MS and their families.
These priorities aim to help people get answers sooner and access appropriate care and support throughout the diagnosis journey. Getting those answers right matters just as much as getting them sooner. As Prof Hardy explains:
“This is why diagnostic accuracy matters so much: we need to make the diagnosis when the evidence supports it, but we must also be prepared to revisit it when the clinical picture doesn’t fit.”
