Understanding Dementia: Types & Stages

Written & reviewed by the BestDoctors.sg editorial team · Last updated 29 Aug 2026 · General information, not medical advice

Why the type matters

It is tempting to treat dementia as one thing, but the underlying disease shapes the early symptoms, how it progresses and how it is best supported. Knowing the type also affects safety: for example, some medications used for agitation can be dangerous in dementia with Lewy bodies, so prescribing must always be left to a doctor who knows the diagnosis. As the Alzheimer’s Society notes, most people should not try to work out the type themselves – that is a job for a proper assessment – but understanding the broad categories helps families make sense of what they are seeing.

Alzheimer’s disease

Alzheimer’s disease is the most common cause of dementia. It usually begins gradually, most often with memory problems – forgetting recent events, names or words – alongside difficulty with thinking and reasoning, language and visual perception, and changes in mood. It is driven by changes in the brain involving abnormal proteins, and the risk rises with age. Some people first have milder changes, sometimes called mild cognitive impairment, before symptoms cross the threshold into dementia. Because the onset is slow and insidious, families often realise only in hindsight how long the changes had been building.

Vascular dementia

Vascular dementia is the second most common type and is caused by reduced blood flow to the brain, for example after strokes or damage to small blood vessels. Its early signs are often different from Alzheimer’s: problems with planning, concentration and the speed of thinking may come before obvious memory loss. It can progress in a “step-wise” pattern, with periods of stability and then sudden changes, and may include brief episodes of confusion. Because it is linked to vascular health, managing blood pressure, diabetes and other risk factors matters, and stroke symptoms should always be treated as an emergency.

Lewy body and frontotemporal dementia

Dementia with Lewy bodies has some distinctive features: fluctuating attention and alertness that vary through the day, visual hallucinations, movement problems similar to Parkinson’s disease such as stiffness and slowness, and disturbed sleep in which people seem to act out dreams. Frontotemporal dementia often begins at a younger age, commonly between the mid-forties and mid-sixties, and its early symptoms are typically changes in personality and behaviour, or difficulties with language, rather than memory loss first. Recognising these patterns helps families understand behaviour that might otherwise be confusing or upsetting.

Mixed and young-onset dementia

Many people, especially older adults, have more than one type at the same time – most commonly Alzheimer’s disease together with vascular dementia – which is called mixed dementia, and the symptoms of each overlap. Dementia that begins before the age of 65 is known as young-onset dementia; its early symptoms are less likely to be memory problems and more likely to involve behaviour, language or vision. There are also rarer and sometimes treatable conditions, such as normal pressure hydrocephalus or alcohol-related brain damage, which reinforces the value of a thorough assessment rather than assumptions.

The stages of dementia

Dementia is often described in three broad stages, but the Alzheimer’s Society is clear that it affects everyone differently, so think of these as a guide rather than a fixed timeline. In the early or mild stage, symptoms interfere with daily life but the person still does much independently: forgetting recent conversations, word-finding trouble, misplacing things, repeating questions, or difficulty with complex tasks like finances. The middle or moderate stage is usually the longest and needs more help – with washing, dressing and using the toilet – alongside more confusion, not recognising familiar people, and a higher risk of getting lost.

The later stage

In the late or severe stage, a person needs constant care, often professional, and loses much awareness of recent experience and surroundings. They may need help with eating, drinking and moving, communication becomes very limited, and they become more vulnerable to infections such as pneumonia. This is a hard stage for families, but comfort, dignity and gentle presence remain deeply valuable, and palliative support can help. A separate guide in this series looks at later-stage and end-of-life care. How quickly someone moves through the stages varies widely from person to person and depends on their overall health.

How dementia is diagnosed in Singapore

There is no single test for dementia. A diagnosis is built up from a detailed history – ideally with input from someone who knows the person well – checks to rule out reversible causes such as B12 deficiency, thyroid problems or infection, a medication review, memory and thinking tests, and sometimes brain scans. In Singapore, the usual pathway starts with a GP, family doctor or polyclinic, which can do an initial assessment and refer to a hospital memory clinic for formal diagnosis and specialist workup. Community mental health teams also screen and support. A formal diagnosis is worth pursuing because it unlocks treatment, planning and support.

Related dementia topics

• Living with dementia
• Communicating with someone who has dementia
• Managing behaviour & mood changes
• Daily & personal care
• Home safety & preventing wandering
• Eating, nutrition & swallowing
• Supporting yourself as a caregiver
• Planning ahead: legal & financial
• Later-stage dementia & end-of-life care
• Geriatricians in Singapore

Sources

• Alzheimer’s Society – Types of dementia: alzheimers.org.uk
• Alzheimer’s Society – Alzheimer’s disease: alzheimers.org.uk
• Alzheimer’s Society – Progression and stages of dementia: alzheimers.org.uk
• Dementia UK – Types of dementia: dementiauk.org
• Alzheimer’s Association – Stages of Alzheimer’s: alz.org
• NHS – Dementia guide: nhs.uk