What Is Multiple Sclerosis? An Australian Guide

What is multiple sclerosis? An Australian guide

Multiple sclerosis is the most common chronic neurological disease of young adults in Australia, and it is also one of the most misunderstood — including, as we will get to, by the people who assess NDIS plans.

Part of the problem is that MS is genuinely hard to describe. It is not one thing that happens once. It is a process that unfolds over decades, differently in every person, with symptoms that can come and go, change, resolve completely, or never resolve at all. Two people diagnosed on the same day in the same clinic can have entirely different lives twenty years later. That variability is not a failure of medicine to pin it down. It is the disease.

This guide is for people who have just been diagnosed, for families trying to understand what they have been told, and for support workers who have been rostered to someone with MS and given a one-line handover. It covers what MS is, what the Australian data actually shows, and — importantly — what a diagnosis does not tell you.

What is happening in the body

The central nervous system — brain, spinal cord and optic nerves — runs on electrical signals. Nerve fibres carrying those signals are wrapped in myelin, a fatty insulating sheath that works much like the plastic coating on an electrical cable. Myelin makes signals travel fast and cleanly.

In MS, the immune system attacks myelin in the central nervous system. Where it strips the coating away, signals slow down, scatter or stop. The patches of damage are called lesions or plaques, and the scarring they leave behind is where the name comes from: multiple (many) sclerosis (scars).

What symptom a person gets depends entirely on where the lesions are. A lesion on the optic nerve causes blurred or double vision. One in the spinal cord causes numbness, weakness or bladder problems. One in the cerebellum causes tremor and balance problems. One in the frontal lobe might cause nothing noticeable at all — a substantial proportion of MS lesions are silent, visible on MRI without ever producing a symptom.

Two further processes matter and are less often explained.

Remyelination. The body can partially repair myelin, which is why many early MS symptoms resolve, sometimes completely. This is the biological basis of a relapse followed by a remission. The repair is imperfect and gets less effective over time.

Axonal loss and neurodegeneration. Underneath the relapses, there is a slower, quieter process in which nerve fibres themselves are lost and brain volume shrinks. This is what drives progressive disability, it happens from early in the disease, and it correlates far better with long-term outcomes than relapse counts do. It is also why the modern treatment goal is not “prevent relapses” but “prevent progression,” and the two are not the same.

The types, and what they actually mean

MS is classified by its course, not its severity. The classification matters because it determines what treatment is available.

Relapsing-remitting MS (RRMS) is the pattern at diagnosis for about 85% of Australians with MS, per MS Australia’s key facts. Attacks of new or worsening symptoms lasting more than 24 hours, developing over hours to days, followed by partial or complete recovery over weeks to months, with stability in between. The relapses are the visible part; the neurodegeneration continues between them.

Secondary progressive MS (SPMS) is what RRMS becomes in many people after years or decades — a shift from discrete attacks to steady accumulation of disability, with or without occasional relapses on top. There is no test that marks the transition. It is usually identified retrospectively, which means a great many people are in it for a year or two before anybody says so.

Primary progressive MS (PPMS) affects about 12% from the outset: steady progression from the first symptom with no distinct relapses. It is diagnosed later on average, is more common in men, and tends to present with gradually worsening walking.

Clinically isolated syndrome (CIS) is a single episode that looks like MS but does not yet meet the criteria. Many but not all people with CIS go on to a diagnosis.

Radiologically isolated syndrome (RIS) is MS-typical lesions found incidentally on an MRI done for something else, in a person with no symptoms at all. This used to be a watch-and-wait situation; as of the 2024 diagnostic criteria, some of these people can now be formally diagnosed with MS.

A note on language. “Benign MS” is a term you may encounter and should treat cautiously — it can only ever be applied retrospectively, after decades, and people told they had benign MS have gone on to significant disability. “Malignant” or “aggressive” MS likewise describes a course observed, not a category assigned at diagnosis.

The 2024 McDonald criteria: why diagnosis is changing

Diagnosis is made using the McDonald criteria, which were substantially revised in 2024 and published in Lancet Neurology. If you were diagnosed before this, the landscape has moved, and it is worth knowing how.

The underlying logic has always been to demonstrate damage in more than one place (dissemination in space) and at more than one time (dissemination in time). The 2024 revisions change both.

• The optic nerve is now a fifth lesion location, alongside periventricular, cortical/juxtacortical, infratentorial and spinal cord. Evidence can come from orbital MRI, optical coherence tomography showing inter-eye differences in retinal layer thickness, or abnormal visual evoked potentials — and it counts even if the optic nerve involvement never caused symptoms.
• Dissemination in time is no longer mandatory. With a typical attack or at least 12 months of progression, MS can be diagnosed where four of the five locations show typical lesions.
• The kappa free light chain index in cerebrospinal fluid is now accepted as an alternative to oligoclonal bands.
• Two MRI findings have entered the criteria: the central vein sign, which distinguishes MS lesions from those caused by vascular disease or migraine, and paramagnetic rim lesions, which are highly specific to MS and also carry prognostic weight — four or more are associated with greater disability accumulation.
• Relapsing-onset and progressive-onset MS now sit in one unified framework, and for primary progressive MS two or more spinal cord lesions can satisfy dissemination in space without any brain lesions.

Why this matters practically: diagnosis has historically taken about two years from first symptom, and roughly 20% of people diagnosed with MS may be misdiagnosed. The revisions are designed to shorten the delay so that treatment can start earlier, which is where the strongest evidence of benefit sits. They also add caution for people over 50 and those with vascular risk factors, who need additional confirming features.

The Australian numbers

Australia has unusually good MS data, because the Australian MS Longitudinal Study has been running for years and MS Australia commissions periodic prevalence and economic reports. The most recent is the 2025 prevalence and health economic impact report.

37,756 Australians were living with MS in 2024, with a plausible range of 35,621 to 43,277.

Crude prevalence is 139.2 per 100,000, up from 95.6 per 100,000 in 2010.

Prevalence rose 13.3% since 2021 and 47.4% since 2017. That is a steep climb over seven years, and it is not fully explained. Better and earlier diagnosis accounts for part of it. Longer survival accounts for part. Genuine increases in exposure to known risk factors — low vitamin D, smoking, obesity in adolescence, glandular fever — probably account for the rest.

About 79% of people in the longitudinal study are women, and MS Australia puts it as three in four Australians diagnosed being women. The ratio has been widening over decades, which is itself a clue that environmental rather than genetic factors are driving the increase.

Average age at diagnosis is 20 to 40. This is the defining feature of MS as a social problem: it arrives in the years when people are building careers, forming relationships and having children.

62% — 23,217 people — were on a disease-modifying therapy in 2024.

The latitude gradient, which is striking in Australia

MS prevalence rises the further you live from the equator, and Australia spans enough latitude to show it clearly. Age-adjusted rates per 100,000 in 2024:

Tasmania’s rate is about five times the Northern Territory’s and nearly double Queensland’s or Western Australia’s. The 2024 regression works out at roughly five additional cases per 100,000 for every degree of latitude further south.

The leading explanation is sun exposure and vitamin D in childhood and adolescence, probably interacting with other factors. It is not the whole story — genetics and ancestry vary across the country too — but the gradient appears on every continent that has been studied and is one of the most reproducible findings in MS epidemiology.

What MS costs

The same report puts the total societal cost at $3.004 billion in 2024, up 71.5% from 2017 in nominal terms and 37.5% after inflation. That works out at $79,581 per person per year, roughly seven times average health spending per Australian.

The breakdown is instructive. Direct costs are $43,827 per person (55%), indirect costs $27,906 (35%), and informal care $7,849 (10%). The two largest single components are employment and productivity loss at $846 million ($22,411 per person) and disease-modifying therapies at $592 million ($15,671 per person).

And the cost climbs steeply with disability: $42,688 per person with no disability, $69,759 mild, $99,328 moderate, $135,780 severe. Which is the economic case for treating early and treating well, made in dollars.

What causes MS

The honest summary: MS requires a genetic susceptibility plus environmental triggers, and the environmental side has become much clearer in the last few years.

Epstein-Barr virus is now considered the leading cause. A 2022 study in Science followed more than 10 million young US military personnel, 955 of whom developed MS, and found that MS risk rose about 32-fold after EBV infection — with no equivalent rise after infection with other viruses. The senior author described it as the first compelling evidence of causality.

That finding needs context. EBV infects the overwhelming majority of adults worldwide and almost nobody who gets it develops MS. So EBV is best understood as necessary but nowhere near sufficient — a trigger that, in a genetically susceptible person exposed to other risk factors, can set the process going. It also opens a genuinely hopeful door: MS Australia notes that an effective EBV vaccine might prevent as much as 90% of cases.

The other established modifiable risk factors are low vitamin D / low sun exposure, smoking (including passive smoking), adolescent obesity, and glandular fever specifically, as distinct from asymptomatic EBV infection. Global experts estimate that addressing smoking, vitamin D deficiency, obesity and glandular fever could prevent around 60% of cases.

Genetics plays a role but a modest one. MS is not inherited in any straightforward way. More than 200 genetic variants have been associated with it, each contributing a small amount. The risk to a child of a parent with MS is a few per cent — higher than the general population, low in absolute terms.

What a diagnosis does not tell you

This section exists because it is the question everybody asks and nobody can answer.

A diagnosis of MS does not tell you whether you will use a wheelchair. It does not tell you whether you will keep working. It does not tell you how long you will live — life expectancy in MS is modestly reduced, not dramatically so, and the gap has been narrowing. It does not tell you how many relapses you will have or when.

What it does tell you is that you have a condition that needs active management, that starting an effective disease-modifying therapy early is the single most evidence-backed thing you can do, and that the trajectory you are on is more modifiable now than at any previous point in the history of the disease.

Some rough signposts, offered with the caveat that they are population averages and your neurologist’s read of your own MRI and clinical picture is worth more than any of them: the large majority of people with MS continue walking independently for many years; most people with MS do not become severely disabled; the proportion of people with MS who are significantly disabled has been falling as treatment has improved. The grim statistics that circulate online are mostly from the pre-treatment era.

The measure you will encounter is the EDSS — the Expanded Disability Status Scale, running 0 to 10. The 2025 Australian report groups it as no disability (0), mild (1.0–3.5), moderate (4.0–6.0) and severe (6.5–9.5). It is heavily weighted toward walking, which is its main criticism: it captures mobility well and fatigue, cognition and bladder function badly. A person with an EDSS of 2 can be severely limited by fatigue and cognitive change, and the number will not show it.

What MS is not

MS is not a muscle disease. It is a disease of the central nervous system. The weakness comes from signals not arriving, not from the muscle failing. This distinction matters for how rehabilitation works.

MS is not muscular dystrophy or motor neurone disease. These get confused constantly. They are entirely different conditions with different courses and prognoses.

MS is not fatal in the way it is often assumed to be. Most people with MS die of the same things as everybody else.

MS is not contagious. EBV is, MS is not.

MS is not a mental health condition — and people with MS also get depression and anxiety at elevated rates, which is a real neurological and situational consequence rather than a character failing. A 2026 MS Australia survey recorded people being told by NDIS assessors that depression is not a symptom of MS. It is, and the brain lesions contribute directly.

MS is not something a person is going to get over. Relapsing-remitting MS involves recovery from attacks, which is different from recovery from the disease. The same survey recorded participants being told that people with relapsing-remitting MS “would get better.” They do not. We deal with the consequences of that misunderstanding in multiple sclerosis and the NDIS.

Where to go next

If you have just been diagnosed, the two guides worth reading are disease-modifying therapies explained — because the early treatment decision is the consequential one — and MS fatigue, because fatigue affects more than 80% of people with MS and is the symptom most likely to shape your daily life.

If you are heading into an Australian summer, read heat sensitivity and MS. Around 80 to 90% of people with MS are heat sensitive and a core temperature rise of a few tenths of a degree is enough to produce symptoms. There is also funding available that most people do not know about.

If you are applying for or arguing about an NDIS plan, start with multiple sclerosis and the NDIS. MS sits on List B, and the way the scheme handles a fluctuating condition is the single biggest source of trouble for Australians with MS.

If you are a support worker, supporting someone with MS is the practical one.

Your state MS organisation is worth contacting regardless: MS Plus in Victoria, NSW, the ACT and Tasmania, MSWA in Western Australia, MS Queensland, and MS Society of SA & NT. They run MS nurse lines, peer programs and advice services, and they know things no website does.