The discriminators (time course does most of the work)
| Feature | Delirium | Dementia | Primary psychosis |
|---|---|---|---|
| Onset | Hours–days | Months–years | Days–months |
| Course | Fluctuating | Progressive | Variable |
| Attention | Markedly impaired | Preserved early | Usually preserved |
| Consciousness/arousal | Altered | Clear until late | Clear |
| Hallucinations | Often visual | Can occur (visual in Lewy body) | Often auditory |
| Cause | Medical/substance | Neurodegenerative/vascular | Psychiatric (± medical) |
| Priority | Emergency — find the cause | Structured workup | Risk + medical screen |
Delirium — the clinical imperative
Core = acute, fluctuating disturbance of attention and awareness from a medical cause. It masquerades as "psychiatric" but the driver is infection, metabolic derangement (Na⁺/Ca²⁺/glucose/uraemia/hepatic), hypoxia, drug toxicity or withdrawal, or a CNS event. Bedside: months‑of‑the‑year‑backwards / serial 7s to expose inattention; formalise with 4AT/CAM. Management: treat the cause, optimise environment/sleep, minimise deliriogenic drugs; reserve low‑dose antipsychotics for dangerous agitation (avoid in Parkinson's/Lewy body — use with great caution).
Dementia — refinements
"Major neurocognitive disorder": acquired decline across ≥1 domain impairing function. Pattern helps (cortical: Alzheimer's, FTD, Lewy body; subcortical: Parkinson's, Huntington's, vascular). Always screen for reversible contributors — B12, thyroid, depression ("pseudodementia"), normal‑pressure hydrocephalus, medication.
Pitfalls
- Labelling acute confusion in an older adult "psychiatric" and missing sepsis/hyponatraemia.
- Superimposed delirium on dementia (very common) — a sudden change on a chronic baseline is still delirium.
Pearls
- 🎯 Acute + fluctuating + inattentive = delirium until proven otherwise.
- 🩺 New psychosis in the elderly = medical workup first; the diagnosis is usually not new‑onset schizophrenia.
Next → The motor‑behavioural emergency hidden in plain sight — catatonia (Concept 16).