What Is Dementia? An Australian Guide

What is dementia? An Australian guide

Dementia is now the leading cause of death for Australians.

That sentence stops people, and it should. On Dementia Australia’s current figures, an estimated 446,500 Australians are living with dementia in 2026, projected to reach 812,500 by 2054 — an 82% increase — and to exceed a million by 2065 without significant intervention. An estimated 1.7 million people are involved in caring for someone with dementia. 54% of people in permanent residential aged care have it.

And around 29,000 of those Australians are under 65.

That last number is the reason this guide series exists in the form it does, and it is worth saying plainly up front: we are an NDIS provider, so the guides here are written primarily for people with younger onset dementia — diagnosed before 65, and therefore in the NDIS rather than the aged care system. If you are over 65 or already in aged care, much of the clinical content still applies and the funding content will not, and the place to start is My Aged Care on 1800 200 422. We set out that boundary honestly in dementia, the NDIS and aged care.

This first guide is for everybody: what dementia actually is, what the types are, and — the part that causes the most avoidable harm — what gets mistaken for it.

Dementia is a syndrome, not a disease

This is the single most important conceptual point and it is routinely muddled, including by clinicians in a hurry.

Dementia is not a diagnosis of a disease. It is a syndrome — a collection of symptoms — defined by progressive decline in cognitive function severe enough to interfere with daily life, caused by disease or injury affecting the brain.

So “she has dementia” is roughly as specific as “he has a rash.” The useful question is always: dementia caused by what?

That matters practically for four reasons. The cause determines the likely pattern of symptoms. It determines the trajectory. It determines whether any disease-specific treatment exists. And in Australia it can determine which funding system applies, because conditions like Huntington’s disease and alcohol-related brain injury sit differently again.

The formal criteria require significant decline in one or more cognitive domains — learning and memory, language, executive function, complex attention, perceptual-motor function, or social cognition — that represents a decline from the person’s own previous level and interferes with independence. Note the breadth of that list. Memory is one of six domains, and some dementias barely touch it early on.

The types, and what actually distinguishes them

Alzheimer’s disease is the most common cause, accounting for the majority of dementia. The classic early pattern is difficulty forming new memories — recent conversations lost while older memories remain — alongside word-finding difficulty and disorientation in time and place. It is driven by amyloid plaques and tau tangles, and it is usually gradual over years.

Vascular dementia is the second most common, caused by disrupted blood supply — one large stroke, multiple small strokes, or accumulated small vessel disease. Its hallmark is a stepwise course rather than a smooth decline, often with prominent slowing, executive dysfunction and gait problems, and relatively preserved memory early on. It is also the most preventable form, because the risk factors are the stroke risk factors. We cover the stroke pathway in cognition and neglect after stroke.

Mixed dementia — usually Alzheimer’s plus vascular — is extremely common and probably more common than pure forms, particularly in older people.

Dementia with Lewy bodies and Parkinson’s disease dementia share a pathology and differ in timing. Features that distinguish them: fluctuating cognition, where someone is markedly better on some days than others; visual hallucinations, often of people or animals, typically well-formed and not frightening at first; REM sleep behaviour disorder, where people act out dreams, sometimes years before any cognitive change; and parkinsonism — tremor, rigidity, slowness.

One critical safety point here: people with Lewy body dementia can have severe adverse reactions to antipsychotic medication, including life-threatening sensitivity. If someone with fluctuating cognition and visual hallucinations is prescribed an antipsychotic for behaviour, that warrants a specific conversation about Lewy body disease first.

Frontotemporal dementia (FTD) is the one that most changes the picture for younger people. It typically begins in the 50s and 60s, and the behavioural variant presents with personality and behaviour change — loss of empathy, apathy, disinhibition, compulsive behaviour, changes in eating — with memory often relatively intact. It gets mistaken for psychiatric illness, mid-life crisis or marital breakdown far more often than it gets diagnosed. It has its own guide: frontotemporal dementia.

Primary progressive aphasia is a related group where language goes first — words, naming, comprehension or speech production — while other cognition holds up initially.

Alcohol-related brain injury, including Wernicke-Korsakoff syndrome, which we cover in the brain injury series because it is usually a single-event injury rather than a progressive dementia: alcohol-related brain injury.

Huntington’s disease, an inherited condition combining movement, cognitive and psychiatric change, typically beginning in the 30s to 50s. It is named on NDIS List B.

Younger onset dementia caused by Down syndrome, where Alzheimer’s pathology is near-universal by 40 — covered in Alzheimer’s disease and Down syndrome.

Rarer causes including Creutzfeldt-Jakob disease, HIV-associated dementia, normal pressure hydrocephalus, and dementia following traumatic brain injury.

Why the type matters more in younger people

In people over 80, dementia is overwhelmingly Alzheimer’s, vascular or mixed, and the type matters less for management.

In people under 65, the distribution is genuinely different. Frontotemporal dementia is far more prominent, as are genetic forms, alcohol-related damage, and dementia secondary to other neurological disease. Which means a younger person who is told “it’s dementia” without a specific cause has not finished the diagnostic process, and should push for one. See getting a dementia diagnosis.

What dementia is not

The misattributions in this section cause more harm than almost anything else in the field.

Not normal ageing

Ordinary ageing slows processing and makes word-finding and name retrieval less reliable. People misplace keys, forget why they walked into a room, and take longer to learn new technology. None of that is dementia.

The distinction worth holding is interference with daily life and decline from the person’s own baseline. Forgetting an acquaintance’s name is ageing. Forgetting the name of your daughter’s husband whom you see weekly, or being unable to follow a recipe you have cooked for thirty years, is not.

Not delirium

This is the most clinically dangerous confusion, and it works in both directions.

Delirium is an acute confusional state, developing over hours to days, with fluctuating attention and conscious level, and it is caused by something physical — infection, dehydration, medication, pain, constipation, surgery, alcohol withdrawal, electrolyte disturbance. It is usually reversible when the cause is treated.

Dementia develops over months to years and is progressive.

Three things follow. An older person who becomes confused suddenly has delirium until proven otherwise, and the workup is urgent — not a dementia assessment. People with dementia are at much higher risk of delirium, so the two frequently coexist, and a sudden worsening in someone with dementia is a medical event rather than progression. And a diagnosis of dementia made during an episode of delirium is unreliable and should be revisited once the person is well.

Not depression

Depression in older people can produce poor concentration, slowed thinking, memory complaints and apparent cognitive decline convincingly enough that it was historically called pseudodementia.

It is also treatable, and it is a common cause of a mistaken dementia diagnosis — and a common cause of a missed dementia diagnosis, because in younger onset dementia the early changes are frequently attributed to depression for years. The Conversation’s analysis of younger onset dementia notes an average four-year diagnostic delay, with dementia often mistaken for depression.

The practical answer: treat the depression properly and reassess. If cognition improves, you have your answer. If it does not, you have excluded something important.

Not mild cognitive impairment

Mild cognitive impairment (MCI) is measurable cognitive decline that does not significantly interfere with independence. It is a risk state, not a dementia diagnosis. A proportion of people with MCI progress to dementia, a proportion remain stable, and a proportion improve — particularly where the cause was depression, sleep apnoea, medication or thyroid disease.

Being told you have MCI is not being told you have early dementia, and the distinction is worth insisting on.

Not a reason to stop looking for treatable causes

Before accepting a dementia diagnosis, a reasonable workup excludes: thyroid dysfunction, B12 and folate deficiency, syphilis and HIV where indicated, calcium and electrolyte abnormalities, liver and kidney dysfunction, depression, obstructive sleep apnoea, medication effects — particularly anticholinergic burden, which is a well-documented reversible cause of cognitive impairment — alcohol, normal pressure hydrocephalus, and structural lesions on imaging.

None of these are exotic. All are commonly missed.

Risk and prevention

The encouraging part, and it is genuinely encouraging: a substantial proportion of dementia risk is modifiable.

The established modifiable factors, drawn from the international evidence, include hearing loss in mid-life — which is why hearing aids matter more than people realise — high blood pressure, smoking, obesity, physical inactivity, diabetes, excessive alcohol, traumatic brain injury, air pollution, depression, social isolation, low education, high LDL cholesterol and untreated visual loss.

Two practical observations. The vascular factors are the same ones that cause stroke, which means blood pressure control is doing double work. And hearing loss and social isolation are the two most under-addressed on the list, both cheap to act on, and both strongly linked.

Prevention is not a guarantee and it is not a moral obligation — people who did everything right develop dementia. But mid-life blood pressure, hearing and activity are worth taking seriously.

The trajectory, honestly

Families ask how long and what happens, and the answers they get are often either evasive or falsely precise.

What is true is that dementia is progressive, that no current treatment stops it, and that the rate varies enormously between people and between causes. Average survival from diagnosis is frequently quoted in the region of eight to ten years, with wide variation — the Sydney FRONTIER work on behavioural-variant frontotemporal dementia, for instance, found average survival of 10.4 years from symptom onset. Some people live two years, some twenty.

The staging language you will encounter — mild, moderate, severe, or early, middle and late — is a rough description rather than a timetable:

Early. Independent in most things, with difficulty in specific areas. Still working in some cases. Compensating, often successfully, and often exhausted by the effort of compensating. This is where most of the planning should happen and usually does not.

Moderate. Needs prompting and supervision for daily tasks. Changed behaviour and confusion more prominent. Cannot be left alone safely for extended periods. This is typically the longest phase and the hardest on families.

Late. Dependent for most personal care, limited communication, mobility and swallowing affected, high medical needs.

Three things worth knowing that cut against the usual framing.

Decline is not linear. People plateau, and they drop suddenly — and a sudden drop is far more often delirium, infection, pain, medication or a change of environment than it is progression. Investigate before accepting it.

Function and capacity are not the same thing. Someone needing help to dress may still be entirely able to decide where they live and who visits.

The person remains. This deserves saying because the public framing of dementia as the loss of a self is both inaccurate and corrosive. Preferences, humour, relationships, emotional responsiveness and the capacity to enjoy things persist far longer than cognition, and services that treat a person as already absent produce worse outcomes than those that do not.

What treatment exists

Cholinesterase inhibitors — donepezil, rivastigmine, galantamine — and memantine are available in Australia on the PBS for Alzheimer’s disease with authority criteria. They produce modest symptomatic benefit in some people for a period. They do not slow the underlying disease, and they are not indicated for frontotemporal dementia, where they can make things worse.

Anti-amyloid therapies have changed the international conversation and their Australian availability has been limited and contested. They are for early Alzheimer’s disease with confirmed amyloid, require infusion and monitoring for brain swelling and bleeding, and the clinical benefit is real but small. Anyone being offered one, here or overseas, should ask about eligibility criteria, monitoring requirements and what the realistic expected benefit is.

Treating everything else is where most of the available gain actually sits: hearing, vision, pain, sleep, mood, continence, medication review, and physical activity.

Where to go next

If you or someone close to you is under 65, read younger onset dementia next. The experience, the services and the funding are all different, and the information written for 85-year-olds does not fit.

If a diagnosis has just been made or is being sought, getting a dementia diagnosis sets out the pathway and what to ask for.

If behaviour is the problem, changed behaviour and dementia.

If you are working out who funds what, dementia, the NDIS and aged care.

The National Dementia Helpline is 1800 100 500, free, 24 hours, staffed by advisors, and run by Dementia Australia. Dementia Support Australia is 1800 699 799, 24 hours, for changed behaviours. Both are genuinely useful and both are under-used.