Dementia

What it is

Dementia is not a single disease but a syndrome, a recognisable pattern of symptoms, caused by diseases or injuries that damage the brain more than would be expected from normal ageing¹. It gets worse over time and, although it is more common after the age of 65, it is not an inevitable part of growing older¹.

Young-onset dementia, in which symptoms begin before 65, accounts for up to 9% of cases¹. Dementia affects carers, families and society as well as the person diagnosed; in 2019 its global cost was estimated at US$1.3 trillion, about half of which was attributed to care given by family members and friends¹.

The main types are vascular dementia, Lewy body dementia, frontotemporal dementia and dementia caused by Alzheimer’s disease¹. Mixed forms, in which more than one disease process is present, are common^1,3.

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Alzheimer’s diseaseFrontotemporal dementiaVascular cognitive impairment

In Alzheimer’s disease, the most common cause, damage usually begins in the memory regions of the medial temporal lobe^1,3.

Frontotemporal lobar degeneration affects the frontal and temporal lobes, which govern behaviour, personality and language^6,8.

Damage to large and small blood vessels reduces the brain’s blood supply; disease of small vessels often affects the deep white matter⁹.

Signs and symptoms

Symptoms depend on the underlying disease and on which parts of the brain are affected, and they usually become more severe over time¹.

• Memory problems, such as forgetting recent events or misplacing things¹
• Difficulty finding words, following conversations, solving problems or making decisions¹
• Getting lost or confused in familiar places, losing track of time and misjudging distances¹
• Changes in mood, personality and behaviour, which sometimes appear before memory problems¹
• Fluctuating attention and alertness, detailed visual hallucinations and acting out dreams during sleep, which are characteristic of Lewy body dementia⁵
• Early changes in social behaviour, such as acting impulsively or inappropriately or seeming to lack empathy, or a decline in language, which are typical of frontotemporal dementia^6,8
• In later stages, needing help with personal care, eating and drinking, moving around and continence¹

Causes and risk factors

Each type of dementia has a different underlying disease, and the boundaries between types are not always clear¹. Age is the strongest known risk factor, but many other factors contribute across the life course^1,2.

• Alzheimer’s disease: the most common cause, linked to clumps of amyloid protein between brain cells and tangles of tau protein inside them^1,3
• Vascular dementia: caused by reduced blood flow to the brain, for example after a stroke or a series of small strokes, which damages and eventually kills brain cells⁴
• Lewy body dementia: includes dementia with Lewy bodies and Parkinson’s disease dementia, both associated with clumps of a protein called alpha-synuclein inside brain cells^3,5
• Frontotemporal dementia: a group of diseases affecting the frontal and temporal lobes, and a common cause of dementia beginning before old age^6,8
• Other causes, including repeated head injuries, certain infections such as HIV, harmful alcohol use and nutritional deficiencies¹
• Fourteen modifiable risk factors: less education, hearing loss, high blood pressure, smoking, obesity, depression, physical inactivity, diabetes, high alcohol intake, traumatic brain injury, air pollution, social isolation, untreated vision loss and high LDL cholesterol²

Genetics

Most dementias are not caused by a single inherited gene^2,3. Common genetic variants alter risk: the best known, the ε4 form of the APOE gene, is associated with Alzheimer’s disease, but many people with Alzheimer’s disease do not carry it and it is not used as a diagnostic test². Dementia risk can be reduced whatever a person’s APOE status².

Frontotemporal dementia has the strongest genetic component: estimates suggest that roughly a fifth to a third of cases are linked to a single-gene variant^2,6,8. The most important genes are MAPT, GRN and C9orf72, and C9orf72 variants can cause frontotemporal dementia, motor neurone disease (amyotrophic lateral sclerosis) or both⁶.

Dementia with Lewy bodies usually occurs without a family history, although rare familial cases exist⁵. Some rare inherited disorders of small blood vessels, such as CADASIL, can cause strokes and problems with thinking and memory³.

What happens in the brain

In every form of dementia, neurons (nerve cells) and the connections between them stop working properly and are gradually lost in regions that support memory, language, reasoning and behaviour³. The types differ in the disease process that causes this damage.

In Alzheimer’s disease, amyloid clumps between neurons and tau tangles inside them, together with inflammation and blood-vessel changes, damage brain cells³. In Lewy body dementia, clumps of alpha-synuclein called Lewy bodies are associated with the loss of neurons that produce neurotransmitters, the chemical messengers between brain cells⁵.

In frontotemporal lobar degeneration, the brain disease underlying frontotemporal dementia, neurons and support cells accumulate abnormal tau or TDP-43 protein, and in 5-10% of patients proteins of the FET family⁸. In vascular cognitive impairment, damage to large and small blood vessels reduces the brain’s blood supply; pure vascular dementia is uncommon, because most people with it also have Alzheimer-type changes⁹.

How it is diagnosed

There is no single test for dementia. Doctors first look for other, potentially treatable causes of memory or thinking problems, and even after assessment it is not always possible to say exactly which type of dementia a person has³.

In India, the ICMR Standard Treatment Workflow for dementia sets out assessment at each level of care, including tests for treatable causes such as thyroid disorders and vitamin B12 deficiency and brain imaging with CT or MRI¹⁴. In the United Kingdom, NICE guidance sets out how dementia should be assessed and diagnosed and how people living with dementia and their carers should be supported¹³.

• A medical history, ideally including an account from someone who knows the person well, and a physical examination³
• Cognitive and neuropsychological tests of memory, language, attention and problem-solving³
• Blood tests for conditions that can cause or worsen symptoms, such as vitamin or hormone problems³
• CT or MRI brain scans to look for strokes, tumours, bleeding or patterns of shrinkage³
• PET scans that detect amyloid and tau, and cerebrospinal fluid tests, in selected cases; blood tests for these proteins are being developed^3,10
• For suspected dementia with Lewy bodies, assessment for REM sleep behaviour disorder and specialised tests such as MIBG heart scintigraphy⁷
• Psychiatric assessment to check whether depression explains the symptoms, and genetic testing when an inherited form is suspected^3,6

How scientists study it

Current treatments

Research frontiers

Living with the condition and seeking help

Occasional forgetfulness is common, but persistent or worsening problems with memory, thinking or behaviour that interfere with daily life are worth discussing with a doctor, since some causes are treatable and a diagnosis opens the way to support^1,3.

People living with dementia can help maintain well-being by staying physically and socially active, keeping up hobbies, writing down tasks and appointments, and having regular health check-ups¹. Planning ahead, for example by choosing trusted people to help with decisions and recording preferences for future care, is easier while decisions can still be made independently¹.

Caring for someone with dementia can be demanding. Carers are encouraged to seek help from family, friends and professionals, take regular breaks and look after their own health; WHO’s iSupport programme offers practical skills and training for carers¹.