Delirium is a state of mental confusion which develops quickly and usually fluctuates in intensity. Rather than being a specific disease, delirium is a syndrome, or group of symptoms, caused by a disturbance in the normal functioning of the brain. The delirious patient has a reduced awareness of and responsiveness to the environment, which may be manifested as disorientation, incoherence, and memory disturbance. Delirium is often marked by hallucinations, delusions, and a dream-like state.

Delirium affects at least one in ten hospitalized patients, and is a common part of many terminal illnesses. Delirium is more common in the elderly than in the general population. While it is not a specific disease itself, patientswith delirium usually fare worse than those with the same illness who do nothave delirium.

There are a large number of possible causes of delirium. Metabolic disordersare the single most common cause, accounting for 20-40% of all cases. This type of delirium, termed "metabolic encephalopathy," may result from organ failure, including liver or kidney failure. Other metabolic causes includediabetes mellitus, hyperthyroidism and hypothyroidism, vitamin deficiencies,and imbalances of fluids and electrolytes in the blood. Severe dehydration can also cause delirium.

Drug intoxication ("intoxication confusional state") is responsible for up to20% of delirium cases, either from side effects, overdose, or deliberate ingestion of a mind-altering substance. Medicinal drugs with delirium as a possible side effect or result of overdose include:

  • Anticholinergics, including atropine, scopolamine, chlorpromazine (an antipsychotic), and diphenhydramine (an antihistamine)
  • Sedatives, including barbiturates, benzodiazepines, and ethanol (drinking alcohol)
  • Antidepressant drugs
  • Anticonvulsant drugs
  • Nonsteroidal anti-inflammatory drugs (NSAIDs), including ibuprofen and acetaminophen
  • Corticosteroids, including prednisone
  • Anticancer drugs, including methotrexate and procarbazine
  • Lithium
  • Cimetidine
  • Antibiotics
  • L-dopa.

Delirium may result from ingestion of legal or illegal psychoactive drugs, including:

  • Ethanol (drinking alcohol)
  • Marijuana
  • LSD (lysergic acid diethylamide) and other hallucinogens
  • Amphetamines
  • Cocaine
  • Opiates, including heroin and morphine
  • PCP (phencyclidine)
  • Inhalants.

Drug withdrawal may also cause delirium. Delirium tremens, or "DT's," may occur during alcohol withdrawal after prolonged or intense consumption. Withdrawal symptoms are also possible from many of the psychoactive prescription drugs.

Poisons may cause delirium ("toxic encephalopathy"), including:

  • Solvents, such as gasoline, kerosene, turpentine, benzene, and alcohols
  • Carbon monoxide
  • Refrigerants (Freon)
  • Heavy metals, such as lead, mercury, and arsenic
  • Insecticides, such as Parathion and Sevin
  • Mushrooms, such as Amanita species
  • Plants such as jimsonweed (Datura stramonium) and morning glory (Ipomoea spp.)
  • Animal venoms.

Other causes of delirium include:

  • Infection
  • Fever
  • Head trauma
  • Epilepsy
  • Brain hemorrhage or infarction
  • Brain tumor
  • Low blood oxygen (hypoxemia)
  • High blood carbondioxide (hypercapnia)
  • Post-surgical complication.

The symptoms of delirium come on quickly, in hours or days, in contrast to those of dementia, which develop much more slowly. Delirium symptoms typicallyfluctuate through the day, with periods of relative calm and lucidity alternating with periods of florid delirium. The hallmark of delirium is a fluctuating level of consciousness. Symptoms may include:

  • Decreased awareness of the environment
  • Confusion or disorientation, especially of time
  • Memory impairment, especially of recent events
  • Hallucinations
  • Illusions and misinterpreted stimuli
  • Increased or decreasedactivity level
  • Mood disturbance, possibly including anxiety, euphoria, or depression.
  • Language or speech impairment.

Treatment of delirium begins with recognizing and treating the underlying cause. Delirium itself is managed by reducing disturbing stimuli, or providing soothing ones; use of simple, clear language in communication; and reassurance, especially from family members. Physical restraints may be needed if the patient is a danger to himself or others, or if he insists on removing necessary medical equipment such as intravenous lines or monitors. Sedatives or antipsychotic drugs may be used to reduce anxiety, hallucinations, and delusions.

Persons with delirium usually have a worse prognosis for the underlying disease than the person without delirium. Nonetheless, those without terminal illness usually recover from delirium. They may not, however, regain all their original cognitive abilities, and may be left with some permanent impairments,including fatigue, irritability, difficulty concentrating, or mood changes.

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