Which of the following is the PRIMARY distinguishing feature of delirium compared to dementia?

Explanation

## Delirium vs Dementia: Key Temporal Distinction **Key Point:** The onset and course pattern is the most clinically useful discriminator between delirium and dementia. ### Delirium Characteristics - **Onset:** Acute (hours to days) - **Course:** Fluctuating, often worse in evening (sundowning) - **Reversibility:** Potentially reversible if underlying cause treated - **Attention:** Markedly impaired, cannot maintain focus - **Consciousness:** Altered (hyperalert, hypoalert, or mixed) ### Dementia Characteristics - **Onset:** Insidious (months to years) - **Course:** Slowly progressive, relatively stable day-to-day - **Reversibility:** Usually irreversible (except rare reversible causes like NPH, subdural) - **Attention:** Relatively preserved until late stages - **Consciousness:** Alert and oriented (until advanced stages) ### Clinical Pearl **High-Yield:** A patient with acute confusion in hours/days = delirium until proven otherwise. A patient with gradual cognitive decline over years = dementia. The temporal profile is the **single best discriminator** in clinical practice. ### Mnemonic: DELIRIUM vs DEMENTIA - **D**elirium = **D**ays (acute onset) - **D**ementia = **D**ecades (chronic onset) | Feature | Delirium | Dementia | | --- | --- | --- | | **Onset** | Acute (hours–days) | Insidious (months–years) | | **Course** | Fluctuating, waxing–waning | Progressive, steady | | **Attention** | Severely impaired | Preserved early | | **Reversibility** | Often reversible | Usually irreversible | | **Consciousness** | Altered | Normal | | **Sleep–wake cycle** | Disrupted | May be disrupted | [cite:Harrison 21e Ch 28]