Telling them apart
| Delirium | Dementia | |
|---|---|---|
| Onset | Hours to days | Months to years |
| Course | Fluctuating, worse at night | Slowly progressive |
| Attention | Impaired — the core feature | Preserved until late |
| Consciousness | Altered | Clear until late |
| Reversibility | Usually reversible | Usually not |
They coexist constantly: dementia is the single biggest risk factor for delirium, and a sudden decline in someone with dementia is delirium until proven otherwise.
Hypoactive delirium — quiet, withdrawn, drowsy — is more common than the agitated form and is routinely missed. It has the worse prognosis.
Finding the cause
Delirium is a symptom of physical illness. In older patients the cause is frequently mundane and often multiple:
- Infection — urinary, respiratory
- Drugs — anticholinergics, opioids, benzodiazepines, steroids; and withdrawal from alcohol or benzodiazepines
- Metabolic — sodium, calcium, glucose, uraemia, hypoxia, thyroid
- Retention and constipation — check for a palpable bladder and do a rectal examination
- Pain, poorly controlled
- Neurological — stroke, subdural haematoma, seizure, meningitis
- Environmental — sensory deprivation, missing glasses or hearing aids, sleep disruption, ICU
Management
Non-pharmacological first, always. This is the intervention with the evidence:
- Reorientation, clocks, familiar faces, family presence
- Glasses and hearing aids returned to the patient
- Mobilise early, preserve the sleep–wake cycle, avoid restraints
- Remove lines and catheters as soon as possible
- Treat the underlying cause and stop the offending drug
Antipsychotics only for severe agitation posing a risk to the patient or others, at low dose, for the shortest time, with a documented plan to stop. They do not shorten delirium and increase mortality in dementia.
Two exceptions where benzodiazepines are the treatment rather than the problem: alcohol withdrawal and benzodiazepine withdrawal.
Dementia: what the work-up must include
Reversible contributors are uncommon but must be excluded: B12, TSH, calcium, glucose, and neuroimaging where the presentation is atypical, rapid, or focal.
Patterns worth recognising:
- Alzheimer's — insidious memory loss first
- Vascular — stepwise, vascular risk factors, focal signs
- Lewy body — visual hallucinations, fluctuating cognition, parkinsonism, and severe neuroleptic sensitivity
- Frontotemporal — younger, personality and language change before memory
- Normal pressure hydrocephalus — gait apraxia, incontinence, cognitive decline; potentially treatable
Address capacity, driving, advance care planning and caregiver support — the parts of the answer that are easy to leave out.