Delirium, also referred to as a confusional state, is defined as an acute, transient, reversible brain syndrome that is characterized by fluctuating disturbances of consciousness, attention, perception, and cognition. There are also disturbances in sleep, appetite, and psychomotor activity. Delirium is an acute confusional state characterized by the following features:

  • Sudden onset of cognitive impairment
  • Disorientation to time, date, place, and/or present situation
  • Clouding of consciousness that fluctuates (lethargic, stuporous, etc.)
  • Impairment in attention and awareness
  • Of relatively short duration (hours to weeks)
  • Perceptual disturbances (e.g., illusions, hallucinations, or delusions)
  • Psychomotor agitation
  • Disturbances in memory and language

Delirium is a disorder of attention and concentration. If a patient is wide awake, alert and has good attention span, then he or she does not have delirium. Patients with dementia and no delirium are usually alert and have good attention span. Depending on the severity of the dementia, they may be slow to process information and have a significant memory deficit, but they can focus and follow what you are saying and doing.

Delirium is commonly seen in the hospital setting, and elderly patients are at a higher risk for developing delirium. Patients with dementia are especially susceptible to delirium, often complicating treatment. Sundowning is a delirium syndrome of confusion and agitation occurring in the late afternoon and early evening. A urinary tract infection (UTI) is the most common cause for delirium in nursing home populations and in older individuals with dementia, particularly women. Delirium can be mistaken for dementia. In some cases, delirium is a symptom of a very serious and life-threatening medical condition.

Making a differential diagnosis between delirium and dementia in the hospital setting can be challenging. A review of the medical and medication history is essential. A careful history to identify the onset and duration of signs and symptoms is extremely important to help distinguish between delirium and dementia. A review of the chart notes made by hospital staff such as nurses, speech therapists, occupational therapists, etc. can reveal fluctuations and periods of confusion over time. Psychosocial evaluations done by the medical social worker can provide important information regarding history of illnesses, medical conditions, and a prior diagnosis of dementia. Information provided by family members is extremely helpful and often essential. According to the DSM-IV, delirium is diagnosed when there is evidence from the history, physical examination, or laboratory findings that the disturbance is caused by the direct physiological consequences of a general medical condition.

Once the cause (or causes of the delirium) is properly treated, the delirium should resolve over hours or days. In some cases it may take weeks to completely resolve. It is only then that a diagnosis of MCI or dementia can be made. Therefore, if delirium is suspected, neurocognitive testing should be postponed until the delirium has completely resolved in order to obtain the most accurate assessment of cognitive functioning.

Causes of delirium / confusional state:

Substance Intoxication:

  • Alcohol
  • Illicit drugs
  • Over-the-counter agents (sleep aids)
  • Prescription medications

Substance Withdrawal:

  • Alcohol (delirium tremens)
  • Illicit drugs
  • Prescription medications

Medical Conditions:

  • High fever
  • Infections (Meningitis, Encephalitis)
  • Head injury (concussion, traumatic brain injury)
  • Seizures
  • Post-operative states
  • Strokes
  • Cardiopulmonary disease
  • Gastrointestinal disturbances
  • Genitourinary abnormalities (urinary tract infection – UTI)
  • Severe blood loss
  • Severe sleep deprivation


Agronin, Marc E. Alzheimer Disease and Other Dementias (3rd Edition), Lippincott Williams & Wilkins, USA, 2014.

American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, 4th Edition. APA: Washington DC, 1994

American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, 5th Edition. APA: Washington DC, 2013

Loring, David W. (Editor) INS Dictionary of Neuropsychology and Clinical Neurosciences 2nd Edition Oxford University Press, New York, N.Y. 2015