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Delirium or dementia? How to tell the difference
Delirium comes on over hours or days and often gets better. Dementia develops over months and years and is long-lasting.
Delirium and dementia are often mixed up, even by professionals. Getting it right is important because the treatment is different. When someone has delirium, they need urgent care and treatment, which often results in improvement and recovery.
The speed of the change
Dementia develops slowly. The diseases behind it, such as Alzheimer’s disease, damage the brain over years, and the changes in memory and thinking build up so gradually that many families only see the pattern when they look back. It may be hard to name the exact day when it began.
Delirium arrives over hours or days, so there is a before and an after. If you can put a date on the change, or even a time of day, think delirium.
Two example cases showing the difference in onset between delirium and dementia.
Consider two women in their eighties. May’s family noticed, over about two years, that she was repeating questions and losing track of her bills. There was no single moment when anything changed; she simply needed more help this year than last. A memory clinic later diagnosed Alzheimer’s disease.
Farida was her usual self on Friday and phoned her son as normal on Saturday morning. By Sunday evening she was accusing her carers of stealing, could not say what year it was, and had been awake all night. Her doctor found a chest infection and dehydration; this was delirium, and within two weeks she was back to herself.
The person may show big changes during the day
Delirium fluctuates. A person can be settled and fairly clear at eleven in the morning, then disorientated and suspicious by teatime. Families describe good hours and bad hours, sometimes good minutes and bad minutes. The symptoms are often at their worst in the evening and overnight.
Many dementias are steadier, with their own slow rhythms. Some differ: dementia with Lewy bodies can cause marked fluctuations and hallucinations, and problems with memory and thinking caused by damage to blood vessels in the brain may change in steps. Even so, any new or clearly worse change needs urgent medical assessment for delirium or another acute medical problem.
Can they follow the conversation?
The central problem in delirium is attention: the person can’t follow the conversation. They lose track mid-sentence, answer the first question and drift during the second, or are too drowsy to attend at all.
In typical early Alzheimer’s disease, memory often fails first while the person may still be able to pay attention. A person may ask the same question three times in an hour, yet follow the conversation while it is happening. Other dementias can present differently. In delirium, attention usually changes suddenly and the person finds it hard to follow the conversation.
The differences at a glance
| Feature | Delirium | Dementia |
|---|---|---|
| How it starts | Over hours or days. You can often put a date on it. | Over months or years. Usually seen looking back. |
| How it runs | Comes and goes through the day. Often worse at night. | Often fairly steady from day to day, although Lewy body dementia can fluctuate and problems with memory and thinking caused by damage to blood vessels in the brain may change in steps. |
| Attention | Poor. The person finds it hard to follow a conversation. | Usually holds in early Alzheimer’s disease; patterns differ in other dementias. |
| Alertness | Often changed: agitated and restless, or sleepy and less responsive. Hard to wake is an emergency. | Usually normal in early Alzheimer’s disease; patterns differ in other dementias. |
| Hallucinations | Common, often visual and frightening. | Less common. A feature of some types, such as dementia with Lewy bodies. |
| Cause | A new physical problem: infection, medication change, dehydration, surgery, pain. | Diseases of the brain, most often Alzheimer’s disease. |
| What happens next | Usually improves when the causes are treated, though recovery can be slow. | Progresses slowly. No cure at present. |
Dementia
changes over months to years
years
Delirium
changes over hours to days
days
Delirium or dementia? (PDF)
Download this table as a printable one-page sheet.
Download Delirium or dementia? (PDF)When the person already has dementia
The person most likely to develop delirium is the person who already has dementia. In hospital, up to half of older people with dementia will develop delirium at some point during the admission. Doctors call this “delirium alongside dementia”, and ward staff see it every week.
It is also the situation in which delirium is most often missed. When someone with dementia gets worse, everyone reaches for the explanation already written in the notes. Families are told the dementia is progressing. Sometimes it is. A sudden drop below the person’s normal level should be treated as possible delirium or another acute medical problem until assessed.
The delirium may also be easy to overlook because there is nothing dramatic to see. In people with dementia, the hypoactive form (quiet, sleepy, withdrawn) is common. Nobody shouts or pulls out a drip; the person simply goes quiet and starts sleeping through visits. On a busy ward that can look like a patient who is no trouble at all.
Delirium on top of dementia carries higher risks than either condition alone: longer hospital stays, more complications, a higher chance of not getting home again, and a higher risk of dying. The earlier it is found, the earlier the causes can be treated.
They say it is BPSD. What does that mean?
BPSD means behavioural and psychological symptoms of dementia. The term covers difficulties such as agitation, suspicion and hallucinations. It describes symptoms, but does not by itself explain why they are happening now. Pain, delirium, medicines, discomfort and the person’s surroundings may contribute. A sudden change still needs assessment: it should not be dismissed because the person already has dementia.
Say what you see
Staff meeting your relative for the first time see a confused older person. They may not know that on Tuesday she was feeding herself and taking an interest. You were. When staff assess for delirium, they check whether there has been a recent change from the person’s normal state. A family member can often help answer that question.
“She has dementia, but this is different. On Tuesday she was feeding herself and chatting. Today she can’t stay awake.”
“This happened over a weekend, not over months. Please could she be assessed for delirium?”
Even experienced clinicians can find this distinction difficult. Once you notice a sudden change, report when it began and ask whether it could be delirium. If staff put the change down to dementia, the Raising concerns with staff page gives examples of what to say.
If the sudden change happens at home
Many episodes of delirium begin at home or in a care home or nursing home. Delirium (acute confusion) needs medical assessment now. Outside a care setting, call local emergency services now. In a hospital, care home or nursing home, tell staff immediately and describe the change from normal. In a care home or nursing home, tell the nurse or person in charge immediately and ask them to arrange medical assessment now. Use the words “sudden change” and “possible delirium”.
- is hard to wake, barely responds, or has collapsed
- is struggling to breathe
- shows signs of a stroke, such as a drooping face, weakness in one arm, or lost or slurred speech
- has hit their head in a fall, particularly if they take blood-thinning medication
- has a seizure (a fit)
- is becoming more unwell in front of you, over minutes or hours rather than days
Delirium (acute confusion) needs medical help even if none of these signs is present. Get help now: who to contact and what to say.
Why the difference is important
The two conditions lead to different actions. A sudden change needs medical assessment now, because there may be a treatable cause behind it. A gradual change over months also needs proper assessment, but on a different timescale: a doctor’s appointment, then usually a memory clinic, over weeks.
Delirium can temporarily make memory, thinking and everyday abilities much worse. A dementia diagnosis should not be based on a poor score on a memory or thinking test during delirium alone: clinicians also need to understand how the person was before the illness.
Care arrangements may still be needed while the person recovers. Ask how possible recovery has been considered, and when the assessment and care plan will be reviewed.
- Most dementias change thinking and memory over months and years. Delirium does it over hours and days.
- Delirium typically fluctuates through the day and is often worse at night. Some dementias can also fluctuate, so any new or clearly worse change still needs urgent assessment.
- Poor attention is central to delirium. In typical early Alzheimer’s disease, the person may often still be able to pay attention.
- Up to half of older people with dementia develop delirium in hospital. A sudden worsening should be treated as possible delirium or another acute medical problem until assessed.
- Quiet, sleepy delirium is the kind most often missed in people with dementia.
- A sudden change needs medical assessment now. Do not wait to see if it settles.
- You know the person’s normal better than anyone. Telling staff what has changed, and how fast, is the most useful thing you can do.
More questions
Does delirium lead to dementia?
Why is she worse in the evening?
All questions families ask