Understanding Dementia

Memory loss is probably the symptom most people associate with dementia, but it is only one part of it. Dementia can affect language, attention, judgement, perception, movement, behaviour and the ability to manage everyday tasks. The pattern depends on the type of dementia, the areas of the brain affected and the individual person.

That is why two people living with dementia can present very differently. One person may repeatedly forget a conversation from a few minutes ago. Another may remember what has been said but struggle to organise the steps needed to get dressed. Someone else may experience visual hallucinations or develop noticeable changes in speech, behaviour or personality.

Understanding those differences makes dementia much easier to recognise in practice.

What is dementia?

Dementia is a syndrome: a group of symptoms associated with an ongoing decline in brain function. It is not a normal part of ageing. The changes are significant enough to affect everyday life, although exactly what becomes difficult and how quickly things change varies considerably from person to person.

The main types include Alzheimer’s disease, vascular dementia, mixed dementia, dementia with Lewy bodies and frontotemporal dementia. Alzheimer’s disease is the most common. A person can also have more than one type of dementia at the same time; Alzheimer’s disease alongside vascular dementia is a common example of mixed dementia.

These names are more than labels. The different types involve different disease processes in the brain, which helps explain why dementia does not have one fixed set of symptoms.

What changes in the brain?

The brain works through networks of nerve cells communicating with each other. Diseases that cause dementia progressively interfere with those cells and their connections. As particular networks become damaged, the functions that depend on them become more difficult.

In Alzheimer’s disease, abnormal accumulation of amyloid and tau proteins is associated with damage to nerve cells. The hippocampus and nearby medial temporal structures, which are important for forming new memories, are commonly affected early. This helps explain why somebody may talk clearly about an event from many years ago but be unable to remember a conversation that took place ten minutes earlier. Alzheimer’s disease is not always memory-led, however; less typical forms can begin with prominent visual or language difficulties.

Vascular dementia results from cerebrovascular disease that damages brain tissue by disrupting its blood supply. This may occur after a stroke, through disease of the small blood vessels in the brain or through multiple areas of vascular injury. The clinical picture depends on where and how much damage has occurred. Problems with processing speed, attention, planning and reasoning can be particularly noticeable, but memory, mood, movement and other functions may also be affected. Not everyone who has a stroke develops vascular dementia.

In dementia with Lewy bodies, abnormal deposits of the protein alpha-synuclein form Lewy bodies within nerve cells. Attention and alertness can fluctuate considerably. Recurrent, well-formed visual hallucinations, REM sleep behaviour disorder and Parkinsonian features such as slower movement, stiffness and gait changes are characteristic features. Memory problems can occur but may be less prominent early in the condition than they often are in Alzheimer’s disease.

Frontotemporal dementia mainly affects the frontal and temporal lobes. These areas contribute to behaviour, judgement, executive function, emotion and language. Some people therefore develop early changes in personality, social behaviour or inhibition; others develop progressive problems with language. Frontotemporal dementia is an important cause of young-onset dementia and can have a genetic basis in some families.

What might this look like in everyday life?

A person who cannot retain new information may ask the same question several times because they genuinely do not remember receiving the answer. Someone whose executive function is impaired may understand that they need to wash but struggle to organise the sequence of actions needed to do it. A person with language impairment may know what they want to say but be unable to find the word.

Changes in visual perception and spatial processing can make an unfamiliar environment much harder to navigate. Add the noise, interruptions, unfamiliar staff and altered routine of a hospital ward and it becomes easier to understand why somebody who manages reasonably well at home may appear much more disorientated after admission.

Behaviour needs interpretation too. Repeatedly getting out of a chair may mean somebody needs the toilet. Pushing a nurse away during personal care may reflect pain, fear or not understanding what is happening. Calling out may be a way of seeking reassurance or expressing a need when finding the words has become difficult.

This is why describing someone simply as having “challenging behaviour” is rarely useful. NICE recommends looking for clinical and environmental causes of distress, including pain and delirium, before moving to treatment.

The main types of dementia

Alzheimer’s disease usually develops gradually. Difficulty learning and retaining new information is a common early feature, followed over time by wider difficulties with orientation, language, reasoning and everyday activities.

Vascular dementia is more variable because vascular injury can affect different parts of the brain. Some people deteriorate after recognisable vascular events; others develop a more gradual decline associated with small-vessel disease. Brain imaging can support the diagnosis, but NICE specifically advises against diagnosing vascular dementia from vascular lesion burden alone.

Dementia with Lewy bodies often produces a mixture of cognitive, perceptual, sleep and movement symptoms. A person may seem strikingly alert at one time and considerably less able to engage later. Visual hallucinations can be detailed and recurrent. Antipsychotic medicines require particular caution because they can worsen motor symptoms and, in some people, provoke severe sensitivity reactions.

Frontotemporal dementia may initially look quite unlike the usual public picture of dementia. Changes in social judgement, empathy, motivation, inhibition, eating behaviour or language may appear before obvious memory impairment.

Mixed dementia means more than one type is present. Alzheimer’s disease and vascular dementia are a common combination, although other combinations occur.

How is dementia assessed?

There is no single test that can diagnose every dementia. Assessment begins with the history: what has changed, when the changes began, whether they have progressed and how they are affecting everyday life. Where possible and appropriate, information from somebody who knows the person well can help establish what has changed from their usual level of functioning.

If dementia is still suspected, NICE recommends physical examination, appropriate blood and urine investigations to look for reversible causes of cognitive decline, and cognitive testing. Validated brief cognitive instruments can support assessment, but a normal score does not rule out dementia.

Other explanations need to be considered. Delirium, depression, sight or hearing impairment and cognitive effects from medicines with an anticholinergic burden are among the factors NICE specifically highlights before referral to a specialist dementia diagnostic service.

If dementia remains suspected after these have been investigated, specialist assessment can establish whether cognitive decline is present and, where possible, identify the subtype. Structural brain imaging is generally offered to help exclude reversible causes and support subtype diagnosis unless dementia is already well established and the subtype is clear.

Further tests are selective rather than routine. For example, NICE recommends MRI when vascular dementia is suspected and the subtype remains uncertain, with CT used if MRI is unavailable or contraindicated. Other investigations such as FDG-PET, perfusion SPECT, cerebrospinal fluid biomarkers or dopamine transporter imaging may be considered in particular diagnostic situations.

When someone with dementia suddenly changes

A patient with established dementia normally chats during breakfast and recognises their daughter when she visits. Today they are unusually drowsy, cannot maintain attention and are much less responsive than yesterday.

That change should not automatically be attributed to dementia.

Delirium is an acute disturbance that develops over hours or days and tends to fluctuate. Dementia develops over a much longer period. A person can have both at the same time, and dementia is itself an important risk factor for delirium.

Infection, hypoxia, dehydration, pain, constipation, urinary retention, medicines and metabolic disturbance are among the problems that may contribute to delirium. If indicators are present in hospital or long-term care, current NICE delirium guidance recommends assessment with the 4AT delirium assessment tool. In critical care or the recovery room after surgery, CAM-ICU or the Intensive Care Delirium Screening Checklist is used instead.

If it is difficult to distinguish dementia from delirium, or delirium superimposed on dementia, NICE advises managing the delirium first.

For a nurse, knowing the person’s baseline can be invaluable. Asking a relative, carer or care-home staff member, “Is this how they usually are?” may be what reveals that an apparently “confused” patient has actually deteriorated acutely.

Treatment depends on the type of dementia

There is currently no cure for the common progressive dementias, but treatment can reduce some symptoms and support independence, function and quality of life.

For mild-to-moderate Alzheimer’s disease, NICE recommends the acetylcholinesterase inhibitors donepezil, galantamine or rivastigmine as treatment options. Memantine is an option for moderate Alzheimer’s disease when acetylcholinesterase inhibitors are not tolerated or are contraindicated, and for severe Alzheimer’s disease. For someone already taking an acetylcholinesterase inhibitor, memantine may also be added as the disease becomes moderate or severe, according to NICE recommendations.

For dementia with Lewy bodies, NICE recommends donepezil or rivastigmine for mild-to-moderate disease and advises considering them in severe disease. Memantine may be considered when acetylcholinesterase inhibitors are not tolerated or are contraindicated.

Acetylcholinesterase inhibitors and memantine are not normally offered specifically to treat vascular dementia unless there is suspected comorbid Alzheimer’s disease, Parkinson’s disease dementia or dementia with Lewy bodies. They are not recommended for frontotemporal dementia.

Medication is only one part of dementia care. NICE recommends activities tailored to the person’s preferences and offers group cognitive stimulation therapy for mild-to-moderate dementia. Cognitive rehabilitation or occupational therapy can also be considered to support functional ability.

Distress is a clinical clue, not just a behaviour to stop

If somebody living with dementia becomes agitated, aggressive or distressed, the first step is not automatically medication. NICE recommends a structured assessment to look for reasons for the distress and to address clinical or environmental causes.

That may mean looking for pain, delirium, infection, constipation, urinary problems, medication effects, hunger, thirst, noise, an unfamiliar environment or care that the person does not understand. Psychosocial and environmental approaches are recommended as initial and ongoing management.

Antipsychotics have a limited role. NICE recommends them only when a person is at risk of harming themselves or others, or when agitation, hallucinations or delusions are causing severe distress. When they are used, the lowest effective dose should be used for the shortest possible time and the need for treatment reassessed regularly.

Nursing someone living with dementia

Good dementia nursing is often found in small decisions.

You may need to introduce yourself several times during a shift. If the person cannot retain the earlier introduction, repeating it is not pointless. From their perspective, they may genuinely be meeting you again.

Give information at a pace the person can follow. One instruction at a time may work better than several together. Allow time for an answer. Check whether glasses and hearing aids are available and working. Speak to the adult in front of you as an adult, even when their cognition is significantly impaired.

Try to preserve function rather than automatically taking over. Somebody who cannot independently complete a whole wash may still be able to wash their face when given the flannel, or choose their clothes even if they need help getting dressed. What a person can still do matters.

Pain deserves particular attention. A person with moderate-to-severe dementia may be unable to describe its location or severity in the usual way. NICE recommends considering a structured observational pain assessment alongside self-report and clinical assessment, or alongside clinical assessment when the person cannot self-report. Behavioural change may be the first clue.

And remember that dementia does not protect somebody from ordinary illness. People living with dementia should have equivalent access to investigation and treatment for other health conditions. New breathlessness is still new breathlessness. A painful abdomen is still a painful abdomen. A sudden reduction in mobility still needs an explanation.

Dementia does not automatically mean lack of capacity

A diagnosis of dementia does not, by itself, tell you whether somebody can make a decision.

Capacity is considered in relation to the particular decision that needs to be made. A person may be able to decide what they want to eat, where they want to sit or whether they want help washing while finding a much more complex decision difficult. Communication also matters: hearing impairment, unfamiliar terminology, fatigue, pain or an unsuitable environment can make decision-making harder.

The legal framework differs across the UK. The Mental Capacity Act 2005 applies in England and Wales. Scotland uses the Adults with Incapacity (Scotland) Act 2000, while Northern Ireland has separate legislation. The exact legal process therefore depends on where you practise, but dementia should never be used as shorthand for “no capacity”.

Capacity can also change over time or with the circumstances surrounding a decision. Bleepbook’s Fluctuating Capacity in Healthcare: Delirium, Dementia & Decision-Making looks at this in more detail.

After the diagnosis

A diagnosis changes more than a medical record. The person and those close to them may be thinking about work, driving, finances, relationships, future care and what increasing support might mean for everyday life.

NICE recommends access after diagnosis to a memory service or equivalent multidisciplinary dementia service, and opportunities to discuss future planning should begin early rather than waiting until decision-making becomes more difficult.

Scotland also has a national policy focus on dementia post-diagnostic support. The Scottish Government’s 2024–2026 dementia delivery plan emphasises person-centred diagnosis, connection to post-diagnostic support, shared decision-making and future care planning. A national evaluation published in September 2026 found continuing variation in how people access and experience that support, so local pathways still matter.

The person is still the person

Dementia can eventually affect many areas of everyday life, but abilities are not all lost at once. Someone who cannot remember what they ate for breakfast may still know exactly which jumper they want to wear. A person who struggles to explain pain may still communicate very clearly that something is wrong. Someone who needs help with personal care can still have strong preferences about how that care is given.

The diagnosis helps us understand what may be becoming difficult. It should never stop us finding out what the person can still do, what matters to them and what has changed today.

References

National Institute for Health and Care Excellence (NICE). Dementia: assessment, management and support for people living with dementia and their carers (NG97).

National Institute for Health and Care Excellence (NICE). Dementia (QS184).

National Institute for Health and Care Excellence (NICE). Delirium: prevention, diagnosis and management in hospital and long-term care (CG103).

NHS. What is dementia?.

NHS. Causes of dementia.

NHS. Treatments for dementia.

Scottish Government. Dementia in Scotland: Everyone's Story – Initial 2-year delivery plan 2024–2026.

Scottish Government. Dementia post-diagnostic support evaluation: final report.