Having had delirium is linked with a higher chance of being diagnosed with dementia later. Most people who have delirium do not go on to develop dementia soon afterwards.
There are two reasons for the link. The first is that delirium can be the earliest visible sign of a brain that was already becoming vulnerable. The illness did not cause the problem. The illness made the existing problem apparent.
The second is that delirium may itself do some harm to the brain, particularly when it is severe or goes on for a long time. Researchers are still working out how much of the link is explained by each of these.
How big is the risk?
Studies suggest that the chance of a later dementia diagnosis is about 2–4 times higher after delirium. This is an association and does not prove that delirium causes dementia.
Part of the link may reflect differences in age, health and early brain changes. Researchers try to take these differences into account, but estimates vary between studies.
The two-to-four-times figure is an average across large groups. It does not predict what will happen to one person.
What to do
Make sure the word delirium appears in the hospital letter, and that their usual doctor knows about it. Mention it before any future operation, because a past episode is one of the strongest warning signs that it may happen again.
Watch memory and concentration over the next few months. Ask their usual doctor for an assessment if they are getting worse rather than better.
And look after the brain in the ordinary ways: hearing aids if they are needed, help from a doctor or nurse to control blood pressure, staying active, and company.
If confusion comes on suddenly again, do not assume dementia has arrived. Ask: could it be delirium?
There is more about the difference between delirium and dementia.
When to get help
Delirium (acute confusion) is a medical emergency. Outside a care setting, call local emergency services now. In a hospital, care home or nursing home, tell staff immediately. Say what has changed and ask whether it could be delirium.