A 75-year-old woman is admitted post-hip replacement surgery. On postoperative day 2 she becomes acutely confused, disoriented to time and place, agitated at night but drowsy during the day, and she is picking at her IV lines believing they are insects. Her nurse notes she was fully oriented on the evening before surgery. Which features of this presentation best distinguish this condition from dementia?
- A Acute onset over hours to days and fluctuating course throughout the day ✓
- B The presence of visual hallucinations and agitation
- C Disorientation to time and place
- D Occurrence in an elderly patient
Correct answer: A. Acute onset over hours to days and fluctuating course throughout the day
Explanation
Delirium is distinguished from dementia primarily by its acute onset (hours to days) and characteristically fluctuating course, with symptoms often worsening at night (sundowning). The level of attention and consciousness is impaired in delirium — a cardinal feature — whereas it is typically preserved until late-stage dementia. Dementia has an insidious onset and follows a more gradual, progressive decline. Visual hallucinations and agitation can occur in both conditions. Pre-existing dementia is the strongest risk factor for developing postoperative delirium.
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.