Acute, fluctuating disturbance of attention and awareness from an underlying medical cause.
Also known as: delirium, acute confusional state, encephalopathy, ICU delirium, sundowning
Overview
Acute, fluctuating disturbance of attention, awareness, and cognition that develops over hours to days, caused by an underlying medical condition, substance, or medication, and not better explained by a pre-existing or evolving neurocognitive disorder.
Epidemiology
Affects 15-25% of hospitalized older adults on general wards, up to 50% post-operatively, and 70-87% of ICU patients. Associated with prolonged hospitalization, functional decline, increased mortality, and persistent cognitive impairment.
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Question 1PsychiatryMedium
A 72-year-old man with no psychiatric history presents with acute onset confusion, disorientation, and visual hallucinations starting last night. He was admitted 2 days ago for a hip fracture. He is pulling at his IV lines. Vital signs show HR 108 and SpO2 94%. He had no cognitive issues prior to admission. What is the most likely diagnosis?
AAlcoholic hallucinosis
BDelirium
CSubdural hematoma
DAcute ischemic stroke
EWernicke encephalopathy
Reveal answer & full explanation
Correct answer: B — Delirium
AAlcoholic hallucinosis
BDelirium✓
CSubdural hematoma
DAcute ischemic stroke
EWernicke encephalopathy
Why Delirium is correct
Delirium is defined by acute onset, fluctuating course, inattention, disorganized thinking, and altered consciousness — his abrupt-onset confusion, disorientation, hallucinations, and agitation in a newly hospitalized older patient fit this picture
Distinguishes from dementia (chronic, stable, no acute onset) and primary psychosis (no medical precipitant, intact consciousness)
In hospitalized elderly, the most common precipitants are infection, medications (opioids, anticholinergics, benzodiazepines), pain, hypoxia, urinary retention, constipation, and sleep deprivation
SpO2 94% suggests hypoxia as a likely contributing precipitant requiring immediate attention
Why the others are wrong
Wernicke encephalopathy — thiamine deficiency from chronic alcohol use or prolonged poor intake produces confusion with ophthalmoplegia and gait ataxia; neither eye movement abnormality nor ataxia is described, and 2 days of hospitalization is too short to deplete thiamine stores in a previously well man
Subdural hematoma — reasonable to consider after a fall, but it typically causes headache, focal deficits, or a steadily declining level of consciousness rather than visual hallucinations with agitation, and it would not explain the tachycardia and borderline oxygen saturation
Acute ischemic stroke — produces sudden focal deficits such as hemiparesis, aphasia, or a visual field cut; global confusion with visual hallucinations and no described focal deficit is not a stroke syndrome
Alcoholic hallucinosis — visual hallucinations beginning a day or two into a hospital stay fit the timing of alcoholic hallucinosis, but in that withdrawal syndrome the sensorium stays clear and the patient remains oriented, and nothing in his history establishes heavy drinking; acute disorientation with agitation in a newly hospitalized, borderline-hypoxic older patient is delirium
Additional high-yield points
Immediate action: identify and treat the underlying cause
Use non-pharmacologic measures first
Low-dose haloperidol or quetiapine only for safety if non-pharmacologic measures fail
Avoid benzodiazepines — they worsen delirium
Question 2PsychiatryMedium
A 78-year-old male with mild dementia is hospitalized with pneumonia. He is lucid and conversant with the team on morning rounds, but by evening he is disoriented to place, pulling at his intravenous lines, and describing cats at the foot of the bed. During the examination he cannot recite the months of the year backward and repeatedly drifts off mid-sentence. Which of the following features best distinguishes delirium from dementia?
AGradual progression of memory impairment over years
BRapid onset with inattention and altered consciousness
CStable cognitive deficits without daily fluctuations
DPreserved sensorium with prominent mood changes
EDisorientation to place with impaired short-term memory
Reveal answer & full explanation
Correct answer: B — Rapid onset with inattention and altered consciousness
AGradual progression of memory impairment over years
BRapid onset with inattention and altered consciousness✓
CStable cognitive deficits without daily fluctuations
DPreserved sensorium with prominent mood changes
EDisorientation to place with impaired short-term memory
Why Rapid onset with inattention and altered consciousness is correct
Delirium has acute onset (hours to days) with a fluctuating course and impaired ATTENTION plus altered consciousness
Delirium is often reversible; the priority is to identify and treat the underlying cause (UTI, pneumonia, electrolyte imbalance, medications)
Stable cognitive deficits without daily fluctuations — describes dementia, which has a stable progression without the fluctuating course of delirium
Gradual progression of memory impairment over years — dementia has gradual onset over months to years with irreversible decline
Preserved sensorium with prominent mood changes — in dementia, attention is usually preserved early; this does not describe delirium
Disorientation to place with impaired short-term memory — the patient is disoriented to place this evening, which makes this tempting, but disorientation and short-term memory loss are common in dementia as well, so they do not separate the two; delirium is distinguished by acute onset and fluctuating course with inattention and altered consciousness
Additional high-yield points
Minimize sedatives in delirium; use antipsychotics only if behavior is dangerous
Lorazepam can WORSEN delirium (it is appropriate only in alcohol withdrawal-related delirium)
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Inattention with acute, fluctuating onset is the hallmark; the Confusion Assessment Method (CAM) operationalizes this.
Differential diagnosis
Dementia — Chronic, slow onset, attention relatively preserved early, level of arousal normal; delirium can be superimposed on dementia (and often is)
Depression (pseudodementia) — Persistent low mood, anhedonia, sleep/appetite changes; cognition impaired but attention often intact; subacute
Primary psychiatric illness (psychosis, mania, dissociative) — Usually younger, preserved level of consciousness, sustained psychotic content, history of mental illness
Nonconvulsive status epilepticus — Confusion without obvious convulsion; EEG diagnostic — must consider in any unexplained altered mental status
Wernicke encephalopathy — Triad of confusion, ophthalmoplegia, ataxia; alcohol use, malnutrition, bariatric surgery, hyperemesis; give thiamine BEFORE glucose
Hypoglycemia or hyperglycemic crises — Fingerstick glucose; rapid reversal with treatment
Diagnostic workup
Diagnostic criteria
DSM-5: (A) disturbance of attention and awareness; (B) develops over short period, fluctuates; (C) additional cognitive disturbance; (D) not better explained by another neurocognitive disorder or coma; (E) evidence of underlying physiologic cause. CAM: (1) acute onset and fluctuating course + (2) inattention + either (3) disorganized thinking or (4) altered level of consciousness.
Drug levels (lithium, digoxin, anticonvulsants); urine toxicology
Troponin and ECG if cardiac etiology suspected
Lumbar puncture if CNS infection or unexplained encephalopathy
Vitamin B12, thiamine (give empirically if Wernicke suspected)
Imaging
CT head if focal deficits, head trauma, anticoagulation, or no identifiable cause
MRI brain if CT non-diagnostic and concern for stroke or PRES
Chest X-ray for occult pneumonia
EEG if nonconvulsive seizures suspected (also shows generalized slowing in metabolic delirium)
Diagnostic algorithm
Feature
Delirium
Dementia
Depression
Onset
Hours to days
Months to years
Weeks to months
Course
Fluctuating, worse at night
Slowly progressive
Persistent low mood
Attention
Markedly impaired
Preserved early
May be mildly impaired
Level of consciousness
Altered (hyper- or hypoactive)
Normal until late
Normal
Orientation
Impaired
Impaired late
Usually intact
Hallucinations
Common (visual)
Late-stage (or DLB)
Rare (psychotic depression)
Reversibility
Usually reversible
Generally not reversible
Reversible with treatment
Distinguishing delirium, dementia, and depression in older adults.
Treatment
First-line
Identify and treat the underlying cause(s) — usually multifactorial (the 'I WATCH DEATH' or similar mnemonic): Infection, Withdrawal, Acute metabolic, Trauma, CNS pathology, Hypoxia, Deficiencies, Endocrine, Acute vascular, Toxins/drugs, Heavy metals
Nonpharmacologic 'HELP'-style bundle (Hospital Elder Life Program): orient frequently (clock, calendar, familiar faces), restore sensory aids (glasses, hearing aids), early mobilization, sleep hygiene (quiet, dark at night; light during day; minimize nighttime interruptions), hydration and nutrition, avoid restraints and tethers
Review and minimize deliriogenic medications: anticholinergics (diphenhydramine, oxybutynin, TCAs), benzodiazepines, opioids (especially meperidine), corticosteroids, H2 blockers; deprescribe when possible
ABCDEF bundle in ICU: Assess/manage pain, spontaneous Breathing trials, Choice of sedation (avoid benzodiazepines; prefer dexmedetomidine or propofol), Delirium monitoring (CAM-ICU), Early mobility, Family engagement
Second-line / adjunct
Pharmacologic treatment ONLY for severe agitation threatening safety after nonpharmacologic measures fail:
Low-dose haloperidol (e.g., 0.25-0.5 mg PO/IM; QT monitoring); avoid in Parkinson disease and Lewy body dementia
Atypicals: quetiapine, olanzapine, risperidone — fewer extrapyramidal effects than haloperidol; in Parkinson disease or Lewy body dementia, if an antipsychotic is unavoidable, use only low-dose quetiapine (avoid risperidone and olanzapine)
Dexmedetomidine (alpha-2 agonist) — in mechanically ventilated ICU patients, suggested over propofol (and preferred over benzodiazepines) for sedation when light sedation or delirium reduction is the priority (SCCM 2025); also used when agitation is preventing ventilator weaning/extubation, but not as routine delirium prophylaxis for all ICU patients (SCCM 2018)
Benzodiazepines ONLY for alcohol/sedative-hypnotic withdrawal delirium or seizures; otherwise worsen delirium
Treat alcohol withdrawal with symptom-triggered benzodiazepines (CIWA) plus thiamine, folate, multivitamins
AVOID physical restraints when possible — increase agitation and injury
Complications
Prolonged hospitalization and higher mortality (in-hospital and at 1 year)
Functional decline and loss of independence
Persistent cognitive impairment and increased risk of subsequent dementia (especially after ICU delirium)
Falls, fractures, pressure ulcers, aspiration pneumonia
Self-injury or injury to staff during severe agitation
Caregiver and family distress
PTSD-like symptoms after ICU stay
PANCE pearls
Delirium is a medical emergency — find the cause. The default assumption in older adults with acute confusion is delirium until proven otherwise.
Hypoactive delirium is MORE common than hyperactive in elderly and is frequently missed — screen all hospitalized older patients (e.g., CAM, 4AT).
If giving glucose to a patient who may be alcohol-dependent or malnourished, give thiamine before or together with the glucose to avoid precipitating Wernicke encephalopathy, but never delay dextrose for hypoglycemia.
Benzodiazepines worsen non-withdrawal delirium — reserve them for alcohol/sedative withdrawal.
Avoid antipsychotics in Parkinson disease and Lewy body dementia (severe neuroleptic sensitivity); use low-dose quetiapine if absolutely needed.
Postoperative delirium peaks on hospital day 2-3; preventive bundles (HELP) reduce incidence by ~30-40%.
References
DSM-5-TR — American Psychiatric Association Diagnostic and Statistical Manual, 5th ed. Text Revision (2022)
SCCM 2018 — Clinical Practice Guidelines for the Prevention and Management of PAD/Delirium/Immobility/Sleep Disruption in Adult ICU Patients (Devlin et al., Crit Care Med 2018)
AGS 2015 — American Geriatrics Society Abstracted Clinical Practice Guideline for Postoperative Delirium in Older Adults (AGS Expert Panel on Postoperative Delirium in Older Adults, J Am Geriatr Soc 2015;63:142-150)
CAM — Confusion Assessment Method (Inouye et al., Ann Intern Med 1990)
SCCM 2025 — A Focused Update to the Clinical Practice Guidelines for the Prevention and Management of Pain, Anxiety, Agitation/Sedation, Delirium, Immobility, and Sleep Disruption in Adult Patients in the ICU (Lewis et al., Crit Care Med 2025;53:e711-e727)
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