Which of the following is the MOST characteristic feature that distinguishes delirium from dementia?

Explanation

## Key Distinguishing Feature **Key Point:** The hallmark difference between delirium and dementia lies in the *temporal profile* and *course* of cognitive dysfunction. ### Delirium Characteristics - **Acute onset**: develops over hours to days - **Fluctuating course**: symptoms wax and wane throughout the day, often worse in evening (sundowning) - **Reversible** if underlying cause is treated - Attention and consciousness are prominently disturbed ### Dementia Characteristics - **Insidious onset**: develops over months to years - **Stable, progressive course**: steady decline without hour-to-hour fluctuation - **Irreversible** (in most cases) - Consciousness and attention are relatively preserved until late stages ### Comparison Table | Feature | Delirium | Dementia | | --- | --- | --- | | **Onset** | Acute (hours–days) | Insidious (months–years) | | **Course** | Fluctuating, variable | Steady, progressive | | **Reversibility** | Often reversible | Usually irreversible | | **Attention** | Markedly impaired | Preserved early | | **Consciousness** | Altered (hyperalert/hypoalert) | Normal until late stage | | **Psychomotor** | Variable (agitated/lethargic) | Normal or slowed | **High-Yield:** In exam questions, if the stem emphasizes *acute onset* and *fluctuating symptoms*, the answer is **delirium**. If it emphasizes *slow progression* and *stable decline*, the answer is **dementia**. **Clinical Pearl:** A delirious patient may appear alert one moment and confused the next; a demented patient shows consistent deficits day-to-day. **Mnemonic:** **DELIRIUM = Acute, Fluctuating, Reversible** vs **DEMENTIA = Chronic, Stable, Irreversible**