What is the Difference Between Delirium and Dementia?

Both delirium and dementia have similar symptoms, but the two medical conditions are not the same. Delirium usually comes on suddenly, and there are ways to prevent it from developing. The onset of dementia is slower, usually taking months or years to develop with minor symptoms sometimes being dismissed as normal forgetfulness or ignored. With this information, you should be able to tell the differences between delirium vs dementia and understand why awareness of delirium and its causes is important.

Some memory lapses are a natural part of aging, but when it is combined with confusion, disorientation, difficulty concentrating, or speech problems, then there is a reason for concern. Since these symptoms can indicate more than one medical condition, an appointment with a doctor should be made to diagnose the condition.

What Is Delirium?

Delirium is a state of abnormal mental confusion caused by the stress of the body or mind. The onset of delirium is usually quick, sometimes developing within a few hours or a few days. There are ways to prevent delirium, which is also known as “acute confusional state” due to its quick onset.

There are several symptoms which indicate a state of delirium, but they can be confused with dementia symptoms due to their similarities. The main symptoms of delirium include:

  • Confusion
  • Disorientation
  • Language Problems
  • Memory Issues
  • Difficulty Paying Attention
  • Poor Concentration

For the most part, delirium affects a person’s attention span, but dementia mainly affects their memory. While delirium is treatable and often preventable, it is incorrectly misdiagnosed in approximately half of all cases. Its diagnosis is also complicated because many dementia patients can also develop delirium.

Causes Of Delirium

Delirium has many causes, some of which are avoidable. The causes include:

  • Infections
  • Dementia
  • Low electrolyte levels
  • Prescription medications
  • Injuries
  • Pain
  • Stress
  • Metabolic disorders

Untreated urinary tract infections, pneumonia, or encephalitis can trigger delirium. Since these infections can be caused by bacteria, although it is rare in the cause of encephalitis, treating the infections with antibiotics will usually resolve the infection and the delirium.

Delirium caused by low electrolyte levels is usually due to severe dehydration or malnutrition, which is why it is important senior citizens, especially those in frail health, need to drink plenty of water. It is important to seek help if loved ones start showing signs of delirium because the dehydration can be fatal.

Along with low electrolyte levels, low levels of the vitamins thiamine and B12 can also cause delirium. People who are alcoholics may have low thiamine levels, and many seniors get regular B12 injections because they cannot absorb the vitamin from the foods they eat. A vitamin B12 deficiency can also cause confusion, memory issues, and dementia.

Delirium is also a side effect of taking certain medications by themselves, in combination with other drugs, or it may appear as a withdrawal symptom after they stop taking certain drugs. Some of the medications associated with delirium include:

  • Pain relievers
  • Antihistamines
  • Medications to help people sleep.
  • Drugs to treat mood disorders like anxiety or depression.
  • Parkinson’s medications
  • Asthma drugs

Unpreventable Delirium Causes

Many patients may enter a state of delirium after head traumas, stress, or if they have dementia. If someone is in an accident and has a head injury, they may wake up confused, disoriented and stressed to the point they become delirious. Fortunately, delirium resulting from a trauma will usually resolve itself by resting and relaxing as the injury heals.

Stress-induced delirium is very common for senior citizens who require hospitalization due to sickness or injuries. Nearly one-quarter of senior citizens will develop delirium while in the hospital, but that figure jumps to almost 70% when they are admitted to an Intensive Care Unit. Delirium is often missed in patients because the only way to diagnose it is by clinical observation and, in busy hospitals, nurses may not have time to carefully observe patients, except in specialty units like an ICU where careful observation is critical.

Since people with dementia are easily confused and disoriented, many of them will develop delirium during a stressful situation, like being in a nursing home. Some dementia patients may suffer from dehydration or malnutrition because due to complications of the disease. In fact, when assessing the risk factors of delirium vs dementia, dementia is on the list. Some of the other risk factors include:

  • Strokes
  • Parkinson’s Disease
  • Being elderly
  • Vision or hearing problems
  • Multiple medical problems
  • History of delirium

Understanding the consequences of delirium, especially as related to dementia, is important because of the complications patients can develop. In some cases, the cause of the delirium can be fatal, such as the case with untreated infections. However, for other patients, the development of delirium can lead to a general decline in their overall health.

Delirium Complications

It isn’t unusual for patients with chronic or terminal illnesses to develop delirium, including dementia patients. The ability to recover from episodes of delirium depends on a person’s mental and physical health before its onset. While people in good health are more likely to make a full recovery, when comparing patients with delirium vs dementia, those with dementia may experience declines in their memory and thinking ability.

Those who have chronic or terminal illnesses may not be able to regain their levels of physical functioning or thinking abilities they had before delirium. Along with a decline in their overall health, some of the other complications patients can develop includes:

  • An increase in injuries due to falls.
  • Weakness
  • Impaired functioning
  • Mobility declines
  • Combative behavior
  • Pressure ulcers
  • Wandering

Some of these complications also occur in patients with dementia whether delirium is present. To better understand the difference between delirium and dementia, it is important to get an overview of what dementia is and what role it plays in the development of delirium.

Defining Dementia

Dementia is the general term for decreases in mental abilities which are so severe that they affect a person’s daily life. Memory loss is a type of dementia, as is Alzheimer’s, which is the most prevalent form as seen on the pie chart. There are several other types of dementia, including:

  • Alzheimer’s
  • Parkinson’s Disease
  • Huntington’s Disease
  • Vascular Dementia
  • Mixed Dementia
  • Dementia with Lewy Bodies (DLB)

Although these, and other types of dementia, may have similar symptoms and causes, they also have unique symptoms and affect the brain in different ways. For instance, the brain of someone with Alzheimer’s will have protein plaque deposits, twisted strands of protein and the brain will also display signs of death. However, the brain of someone with Vascular Dementia will show signs of blood vessel damage, which can appear on brain imaging scans and eliminate an Alzheimer’s diagnosis.

When considering dementia vs delirium, it is important to note three of the main differences: their onset, methods of diagnosis, and their treatments.

The following video sheds some more light on the topic:

Dementia Onset

As stated earlier in the article, delirium rapidly develops within hours or days, but dementia usually develops over time, and it can take several months or years before symptoms are obvious. However, there are cases of acute dementia, which is a rapid onset of the disease. A study from the United Kingdom revealed dementia in some elderly patients was triggered by delirium they developed due to the stress of being in the hospital.

Methods Of Diagnosis

When comparing delirium vs dementia diagnostic methods, no diagnostic tests exist to diagnose delirium, thus, clinical observation is the only method. However, there are several diagnostic and cognitive tests which can help diagnose dementia and its type. Some of the diagnostic tests for dementia include blood tests and diagnostic scans like CT, MRI, and PET scans.

The main cognitive test is the mini mental state examination or MMSE. While this test doesn’t diagnose the disease, it helps to discover a dementia patient’s level of impairment. This test assesses the mental skills like:

  • Long- and short-term memory
  • Attention span
  • Ability to Concentrate
  • Language use and communication abilities
  • Understanding of instructions
  • Planning abilities

It also includes exercises like memorizing a short list and repeating, writing a grammatically correct short sentence and answering time-oriented questions.

Dementia Treatments

While delirium will sometimes resolve itself as the patient heals from the initial cause or they are prescribed rest and relaxation to reduce stress, the treatment of dementia depends on the type a patient has. There are cognitive medications and therapies which can help manage the disease as some forms are irreversible. However, some causes of dementia are resolved with treatments, and the patient’s abilities may slowly return.


Since senior citizens are susceptible to delirium due to several of its causes, it is important to focus on the preventable ones, so it doesn’t develop. Along with preventing delirium, eliminating some causes many also prevent some forms of dementia.

What are your experiences in caring for loved ones with delirium or dementia? We encourage you to share with us in the comment section below.

Sean Byers, MD

Sean Byers, MD

Sean Byers is currently a Resident in the Internal Medicine program at UTMB. He studied at the University of Queensland School of Medicine as well as received his Master’s in Public Health with a focus in epidemiology and biostatistics at the University of Southern California. His background is in biology, computer science, public health, and internal medicine.

Recommended Articles


  • Nursing Times, "Differentiating dementia, delirium and depression", https://www.nursingtimes.net/roles/mental-health-nurses/differentiating-dementia-delirium-and-depression-13-04-2015/
  • Alzheimer's Association, https://www.alz.org/norcal
  • Johns Hopkins Medicine, "Dementia and Delirium", https://www.hopkinsmedicine.org/gec/series/dementia.html#delirium
  • Mayo Clinic, "Delirium", https://www.mayoclinic.org/diseases-conditions/delirium/symptoms-causes/syc-20371386
  • UpToDate, "Patient education: Delirium (Beyond the Basics)", https://www.uptodate.com/contents/delirium-beyond-the-basics
  • NIH, "Vitamin B12", https://ods.od.nih.gov/factsheets/VitaminB12-Consumer
  • Medscape, "Delirium Has Long-Term Consequences for Dementia Patients", https://www.medscape.com/viewarticle/769458
  • Medscape, "Delirium Follow-up", https://emedicine.medscape.com/article/288890-followup#e4
  • Alzheimer's Dementia Alliance of Wisconsin, "Types of Dementia", https://www.alzwisc.org/learn-more/alzheimers-and-dementia-basics/types-of-dementia/
  • The Telegraph, "Delirium 'caused by busy hospitals can trigger dementia in older patients", https://www.telegraph.co.uk/science/2017/01/18/delirium-caused-busy-hospitals-can-trigger-dementia-older-patients/
  • Alzheimer's Association, "How is Alzheimer's Disease Diagnosed?", https://www.alz.org/alzheimers-dementia/diagnosis
  • NHS, "Tests for diagnosing dementia", https://www.nhs.uk/conditions/dementia/diagnosis-tests/
  • NHS, "What are the treatments for dementia?", https://www.nhs.uk/conditions/dementia/treatment/