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Nervous system: Dementia and delirium



Content Reviewers:

Lisa Miklush, PhD, RNC, CNS

The brain is responsible for various mental functions, including memory, thinking, language, behavior, mood, and personality. A decline in at least one of these functions can be caused by either dementia or delirium.

Okay, first, it’s important to differentiate between these two. Dementia is generally caused by structural changes in the brain, has a gradual onset, lasts months to years, and the symptoms usually progress over time.

On the other hand, delirium classically occurs as a consequence of another underlying condition, like an infection or medication toxicity; is acute in onset; lasts only a couple of hours to days; and symptoms fluctuate, meaning they come and go.

Dementia goes through three main stages. In the early stage, the client's memory starts to become impaired, which may lead to repeating conversations or misplacing belongings.

At this point, the client typically recognizes their memory lapses, and this can generate feelings of shame, embarrassment, or frustration.

In the middle stage, the client has trouble identifying common objects or faces and carrying out tasks that involve multiple steps, like grooming or cooking.

Language can also become affected, and they can have trouble processing verbal or written communication. Sometimes, family members notice a change in the client’s behavior or personality. Many clients may also experience loss of bladder control, which can lead to urinary incontinence.

In the late stage, clients become dependent for all everyday activities. Mobility decreases, so they are unable to walk or sit up without assistance.

Ultimately, this can progress to them becoming bed bound. Their ability to swallow food or fluids as well as communicate through language or facial expressions becomes limited or completely lost.

Total urinary and fecal incontinence can also be expected at this point. These clients are also susceptible to respiratory and urinary tract infections, which may lead to serious illness or death.

Okay, now, dementia can result from reversible and irreversible causes. Reversible causes can be controlled and possibly cured with the right treatment.

Some common examples of this include infectious conditions, like syphilis and HIV; dietary deficiencies, especially vitamin B12 deficiency; and hormone imbalances, such as thyroid problems.

Irreversible causes cannot be cured and include Alzheimer disease, which is by far the most common cause of dementia; vascular dementia, which is the second most common cause; frontotemporal dementia; and Lewy body dementia.

Starting with Alzheimer disease. Its exact cause isn't completely understood, but there are abnormal protein deposits between both the neurons, called plaques, as well as inside the cells, called tangles, that get in the way of neuron-to-neuron signaling.

And these neurons that don’t function properly may end up undergoing programmed cell death where they self-destruct.

Next up is vascular dementia, where there’s a progressive loss of brain function caused by poor blood flow to the brain over a long period of time, typically due to a series of strokes, also known as cerebrovascular accidents or brain attacks.

Τhe main risk factor for vascular dementia is atherosclerosis. That’s when there’s a buildup of plaque that thickens and hardens the artery wall.


Dementia and delirium are both conditions that can affect cognitive function, which is the ability to think, remember, and reason. However, they are distinct conditions with different causes and characteristics.

Dementia refers to a decline in a mental function, like memory, language, or behavior that is caused by structural changes in the brain. It is gradual, progressive, and lasts for a long period of time. Dementia can be caused by a variety of conditions, including Alzheimer's disease, vascular dementia, and Lewy body dementia.

On the one hand, delirium has an acute onset and usually results from an underlying disorder or the use of certain medications. Symptoms last only for a while and fluctuate over time. People with delirium can present with disorientation, confusion, agitation, and hallucinations, which often reverse once the underlying cause is treated.