Delirium vs Dementia and depression
How to tell Delirium and Dementia and depression apart when a board question makes them look alike.
Delirium is acute fluctuating inattention; dementia is chronic decline; depression is mood syndrome that can look cognitively slowed.
Side by side
Acute fluctuating disturbance in attention and awareness with altered level of consciousness, often triggered by infection, drugs, withdrawal, metabolic derangement, pain, or hospitalization.
Dementia is chronic progressive cognitive decline with relatively preserved attention early; depression can mimic cognitive impairment with low mood, sleep/appetite change, guilt, and prominent concern about deficits.
Systemic illness or medication/metabolic stress disrupts attention networks and arousal regulation.
Dementia reflects neurodegeneration or vascular injury; depressive cognitive disorder reflects mood-related impaired concentration and psychomotor slowing.
Inattention, waxing-waning course, disorientation, sleep-wake reversal, and reversible medical trigger support delirium.
Gradual decline in independent function supports dementia; depressive symptoms with effort-dependent testing and reversibility support depression-related cognitive impairment.
The trap
All three present as altered cognition in the older patient, and they often coexist (delirium superimposed on baseline dementia is the most common emergency department scenario in elderly). The hallmark of delirium is INATTENTION with acute onset over hours to days, fluctuating course, and an identifiable medical or drug trigger (infection, electrolytes, anticholinergic or opioid medications, benzodiazepine withdrawal, hypoxia, hypoglycemia, urinary retention, pain). Dementia has gradual onset over months to years with preserved attention early; depression has prominent mood symptoms with effort-dependent test performance (the patient often says 'I don't know' rather than guessing) and improves with antidepressant trial (pseudodementia of depression).
The repair move
For any cognitive change in an older patient, work the steps in fixed order: (1) test attention with serial 7s, months backward, or digit span; if inattention is present, work delirium with CBC, BMP, urinalysis, chest X-ray, drug review, pulse oximetry, and glucose; (2) ask about timing (acute hours-to-days is delirium; chronic months-to-years is dementia); (3) screen mood with PHQ-9; a high score with effort-dependent cognitive testing suggests pseudodementia of depression, which responds to an antidepressant trial.
Try a free question
CoreAn hospitalized older adult with pneumonia becomes acutely inattentive, disoriented, and sleepy during the day, then agitated at night. Symptoms fluctuate hour to hour. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Delirium. Acute fluctuating inattention with altered awareness and medical trigger supports delirium.
Why the other choices are tempting
- B. Dementia is chronic progressive decline rather than acute fluctuating inattention.
- C. Depression can slow cognition but does not usually cause fluctuating consciousness.
- D. Alzheimer disease is gradual memory-first dementia.
- E. Frontotemporal dementia is behavior or language-first chronic decline.
Flashcards
Tap a card to flip it.
What cognitive feature best separates delirium from dementia?
Inattention with fluctuating awareness best separates delirium from dementia.
What tempo supports delirium?
Acute onset with waxing and waning symptoms supports delirium.
Quick answers
What is the fastest way to tell Delirium from Dementia and depression?
Delirium is acute fluctuating inattention; dementia is chronic decline; depression is mood syndrome that can look cognitively slowed.
What is the key clue for Delirium?
Acute fluctuating disturbance in attention and awareness with altered level of consciousness, often triggered by infection, drugs, withdrawal, metabolic derangement, pain, or hospitalization.
What is the key clue for Dementia and depression?
Dementia is chronic progressive cognitive decline with relatively preserved attention early; depression can mimic cognitive impairment with low mood, sleep/appetite change, guilt, and prominent concern about deficits.
What is the common trap with Delirium vs Dementia and depression?
All three present as altered cognition in the older patient, and they often coexist (delirium superimposed on baseline dementia is the most common emergency department scenario in elderly). The hallmark of delirium is INATTENTION with acute onset over hours to days, fluctuating course, and an identifiable medical or drug trigger (infection, electrolytes, anticholinergic or opioid medications, benzodiazepine withdrawal, hypoxia, hypoglycemia, urinary retention, pain). Dementia has gradual onset over months to years with preserved attention early; depression has prominent mood symptoms with effort-dependent test performance (the patient often says 'I don't know' rather than guessing) and improves with antidepressant trial (pseudodementia of depression).