A 68-year-old man with a 3-year history of progressive memory loss and cognitive decline is brought to the psychiatry outpatient clinic. His wife reports gradual worsening of orientation and language difficulties. On examination, he is alert and oriented to person only, with a Mini-Cog score of 2/3. His vital signs are stable, and physical examination is unremarkable. Which single feature best distinguishes his underlying condition from acute delirium?

Explanation

## Distinguishing Feature: Onset and Course **Key Point:** The most reliable discriminator between dementia and delirium is the temporal profile of symptom onset and progression. ### Comparison Table: Delirium vs Dementia | Feature | Delirium | Dementia | |---------|----------|----------| | **Onset** | Acute (hours to days) | Insidious (months to years) | | **Course** | Fluctuating, waxing-waning | Gradual, progressive, steady | | **Consciousness** | Altered (hypoactive, hyperactive, mixed) | Alert and awake (until late stages) | | **Attention** | Markedly impaired | Relatively preserved early | | **Reversibility** | Often reversible | Usually irreversible | | **Cause** | Identifiable medical/toxic precipitant | Neurodegenerative or vascular | **High-Yield:** In this case, the **3-year insidious onset with gradual progression** is pathognomonic for dementia. Delirium develops acutely (over hours to days) and fluctuates throughout the day. ### Why This Matters Clinically **Clinical Pearl:** A patient with dementia may *develop* delirium superimposed on their baseline cognitive impairment (e.g., UTI, infection, medication). However, the *underlying dementia* is distinguished by its slow, relentless onset and steady course. **Mnemonic:** **DELIRIUM = ACUTE; DEMENTIA = CHRONIC** - **D**elirium: **D**ays to weeks - **D**ementia: **D**ecades (months to years) [cite:Harrison 21e Ch 25]