Three patients, three stories
- "Yesterday he was fine. Today he's confused, doesn't know where he is, and keeps seeing things." → think delirium.
- "Over two years she's slowly been forgetting, getting lost, struggling with daily tasks." → think dementia.
- "For months he's believed the neighbours are watching him, but he's otherwise alert and attentive." → think psychosis.
The simple way to tell them apart
- Delirium = a sudden problem with attention and awareness (hours to days), and it fluctuates — better one hour, worse the next. Usually caused by a physical problem: an infection, a medicine, dehydration, low oxygen.
- Dementia = a slow, steady decline in memory and thinking over months to years.
- Psychosis = a disturbance of reality testing, usually with clear attention and awareness.
| Delirium | Dementia | Psychosis | |
|---|---|---|---|
| Onset | hours–days (sudden) | months–years (slow) | days–months |
| Course | fluctuates | steadily worsens | variable |
| Attention | markedly impaired | ok early on | usually ok |
| Awareness | clouded | clear until late | clear |
| Usual cause | a physical illness | brain degeneration | psychiatric (± medical) |
The bedside clue and the golden rule
Ask the person to say the months of the year backwards. Real difficulty holding attention points toward delirium.
And a hopeful note: not every memory problem is permanent. Some causes (like a vitamin B12 deficiency or an underactive thyroid) can be treated and reversed.
Quick check ✅
- Which of the three comes on over hours to days and fluctuates?
- Why is sudden confusion treated as an emergency?
Remember this 🌟
Where we're going next → One more emergency you must recognise — the "frozen" patient (Concept 16).