Delirium: Defining a Syndrome Often Mistaken for Dementia

Delirium—a.k.a. acute confusional state—is a medical emergency marked by a fluctuating mental state, confusion, altered consciousness, and unusual behavior.


Delirium shouldn't be confused with dementia, though it can happen, as there are overlapping symptoms.

Photo 43996685 © Ysuel1 -

Delirium is a medical syndrome—not a disease—in which there is a rapid onset of confusion, altered consciousness, and behavioral changes. Unlike dementia, which shares some of these symptoms, the onset of delirium is usually within hours or days (as opposed to months or years).

Delirium is considered a medical emergency. Sufferers (or, more likely, people close to them) should seek medical advice immediately, so that accurate diagnosis and prompt treatment can be initiated. It’s usually reversible, but if not treated correctly, it can lead to long-term disability and even death. The mortality rate is estimated to be 10 to 26 percent, or even higher if it develops in patients who are already critically ill.

Risk Factors For Developing Delirium

Risk factors can fall into one of two categories: predisposing and precipitant factors. Predisposing factors include being over 70 years, dementia, functional disabilities, poor vision, poor hearing, mild cognitive impairment, and alcohol abuse.

Precipitating factors include medication, drugs, surgery, anesthesia, high pain levels, anemia, infections, acute illness, and acute exacerbation of chronic illness.

One systematic review found that 10 to 31 percent of new hospital admissions met criteria for delirium, and between 3 and 29 percent of people admitted to a hospital went on to develop delirium during admission.

The rate of developing delirium was around 80 percent for those in intensive care units. In the post-operative period, it developed in 5 to 10 percent of people following general surgery and 42 percent following orthopedic surgery.

As people near death, around 80 percent will develop delirium. The risk of delirium increases with age, and it’s very common in nursing home residents.

Dementia is one of the strongest risk factors, being present in 25 to 50 percent of people with delirium.

Symptoms of Delirium

Delirium symptoms include:

  • Confusion
  • Disorientation
  • Fluctuating consciousness or periods of unconsciousness
  • Unusual behavior or thinking (cognitive problems)
  • Poor attention or difficulty shifting attention
  • Memory loss or distortion
  • Hallucinations: auditory or visual
  • Emotional outbursts
  • Unusual speech or slurring
  • Muscle control problems including tremor and uncontrollable movements

Causes of Delirium

The mechanism of delirium is not fully understood by doctors, but experts have theorized that it’s caused by an imbalance in the neurotransmitters or by inflammation. Delirium also may result from a wide variety of structural or physiological insults to the body and brain, including:

  • Hypoxia (low oxygen)
  • Hypoglycemia (low blood sugar) and other metabolic imbalances
  • Hyperthermia (low body temperature)
  • Cancer, especially if metastasized (spread from primary location)
  • Structural lesions of the brain, including head injury, tumor, abscess
  • Organ problems and failure including that of the: heart, kidneys, liver, lungs, and thyroid
  • Severe pain
  • Infections, especially when they reach the level of septicemia, pneumonia or meningitis. Urinary tract infections are a common cause.
  • Medication overdose or allergy
  • Poisoning
  • Alcohol or drug abuse and withdrawal (alcohol withdrawal is called delirium tremens)
  • Carbon monoxide poisoning
  • Neurological disorders like Parkinson’s, seizures, TIA (mini-stroke), stroke
  • Mental illness, including schizophrenia and bipolar disorder
  • In the elderly, delirium can be caused even by mild dehydration and a change of environment
  • Miscellaneous causes, include sensory deprivation, sleep deprivation, fecal impaction, urinary retention
  • End of life

Delirium symptoms usually come on suddenly over a few hours or days, but then may fluctuate over time. Delirium can last hours or weeks; symptoms can remain for a time even after the underlying cause has been treated. While it can occur at any age, is more common in the elderly.

Diagnosing Delirium

A physician will make the diagnosis of delirium based on clinical symptoms and signs. He or she may use an assessment instrument like The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), The Confusion Assessment Method (CAM), or the Delirium Symptom Interview (DSI).

Laboratory tests cannot diagnose delirium, but they can help determine the underlying cause. The clinical team will order a series of tests, based on clinical findings that may include blood and urine tests, X-rays, CT or MRI scan of the head, electroencephalogram (EEG), lumbar puncture, pulse oximetry (to diagnose low oxygen), and an electrocardiogram (EKG/ECG).

Treating Delirium

The goal of delirium treatment is to determine the cause and then to stop or reverse it. Hospital admission is usually needed to diagnose and stabilize the patient. Initially, the patient will be given oxygen and be placed on an IV drip until a treatment plan is developed.

The sufferer may also need therapy to help with reorientation, recovery of memory, motor and cognitive skills. It may take several months to recover back to normal function.


A close family friend, let’s call him Stan, developed delirium. He was a fit and healthy 70-year-old who could easily walk 10 miles in any one day.

One afternoon, he visited a family member of mine, and initially he seemed fine. Then he became increasingly agitated and started saying very odd things. He mentioned a dark shadow in the corner of the room and said he thought people were out to kill him.

My quick-thinking (and somewhat terrified) relative called for help, and soon an ambulance was on its way. By the time they came, he was wielding a kitchen knife. He was admitted to hospital and, once stable, transferred to a geriatric ward.

The doctors were puzzled about what caused the sudden deterioration in a previously fit man, especially after their investigations showed that he seemed pretty normal. After a few days my family asked me to visit him and talk to the doctors, physician to physician.

When I visited him, he was having one of his more lucid moments, so I started asking him questions. Always the great storyteller, he began telling me an anecdote from when he was a young man working in the shipyards in the U.K. One of his friends accidentally knocked something in the ship and was covered in asbestos. They stood around him and teased him for looking like a snowman!

As you may know, asbestos is a carcinogen, and none of the men wore any protection. Stan had not mentioned to the doctors that he had worked in the shipyards as a young man, and would have been exposed to asbestos. I passed along this information to his doctor, and on review of the chest X-ray and further tests, it was confirmed that the cause of his delirium was undiagnosed mesothelioma.

Mesothelioma is a rare cancer of the tissue that lines your lungs, stomach, heart, and other organs (the mesothelium). It’s caused by exposure to asbestos, and it usually starts in the lungs but can also start in the abdomen or other organs. It can be benign (not cancer) or malignant (cancer.)

Treatment options, according to the Mesothelioma Veterans Center, range from basic chemotherapy to experimental surgeries. Patients who find a team of Mesothelioma Specialists often have the longest survival times.

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Leonaura Rhodes, MD

Dr. Leonaura Rhodes is a physician turned author, coach, and freelance medical writer and editor. She has worked for Belvoir Media since 2017 and has authored hundreds of articles on … Read More

View all posts by Leonaura Rhodes, MD

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