Adj Asst Prof Lim Si Ching, Senior Consultant, Department of Geriatric Medicine, Changi General Hospital (CGH), a member of the SingHealth group explains the difference between dementia and delirium. 

Dementia: What it is

Dementia is a broad category of brain diseases that causes a slow, chronic decline in brain function. These diseases include Alzheimer’s, stroke (vascular dementia), a combination of Alzehimer’s disease and vascular dementia, Parkinson’s disease and Lewy Body dementia. There are currently more than 70 diseases that can cause dementia, with Alzheimer’s disease being the most common.

Dementia typically affects the elderly, but it can also present in people under the age of 65, known as early onset dementia. This condition is more likely to be hereditary and is devastating to both the patients and their family as the patient is usually still in the productive years of his or her life.

Delirium: What it is

Delirium is a condition that causes a change to the brain’s function. It typically occurs over a few hours to days and has an underlying medical cause. Another feature of delirium is a fluctuation in consciousness levels, with periods of drowsiness alternating with periods of hyper-vigilance. After the underlying medical condition has been treated, the patient’s brain should revert to its normal state. In some cases, it may take up to six months for the patient to fully recover.

Here’s a quick look at the differences between dementia and delirium:

​Dementia ​Delirium

A slow progressive condition that spans many years

​Starts abruptly, emerging over hours or days

​Does not disturb consciousness levels

​Causes consciousness levels to fluctuate between hyper-vigilance and drowsiness

​Is permanent

​Is reversible

​Signs and symptoms are fairly consistent

Symptoms fluctuate over hours, several times during the day

​Behaviour is fairly consistent from day to day, unless there are recent changes in medical conditions or medications

​Patient may exhibit new changes in behaviour, become more agitated and restless


Read on to learn about the symptoms of dementia and how it impacts behaviour.

Ref: O17