Delirium Superimposed on Dementia

Delirium superimposed on dementia is an acute decline in attention and awareness on a background of established cognitive impairment. It is hard to recognise because the baseline is abnormal.

A large proportion of hospitalised older people with dementia develop delirium, and dementia is the strongest risk factor for delirium. One episode accelerates the progression of dementia.

Pathophysiology. Reduced cognitive reserve and neurodegeneration make the brain vulnerable to minor insults. Systemic inflammation produces exaggerated microglial responses, and cholinergic deficit, sleep disruption and drug sensitivity worsen the effect.

An acute change from baseline over hours to days: more confusion, fluctuating alertness, inattention, new agitation or withdrawal, hallucinations, sleep reversal, reduced eating and new incontinence. Family or carers usually notice that "something is different". Complications include falls, functional loss, institutionalisation and death.

Ask carers about baseline function and the onset of change. Screen with a validated tool that allows for dementia and test attention. Search for precipitants: infection, constipation, retention, pain, dehydration, drugs, hypoxia, metabolic disturbance and unfamiliar surroundings. Investigate for the usual causes of delirium, with imaging if focal signs, a fall or anticoagulant use.

Differential diagnosis.

• Behavioural and psychological symptoms of dementia without delirium.
• Lewy body dementia with fluctuating cognition.
• Depression, non-convulsive seizures and subdural haematoma.

Find and treat the cause. Keep the person in a familiar, calm setting with consistent carers, personal items, glasses, hearing aids, hydration, regular toileting and mobility. Avoid restraint and physical catheters. Avoid antipsychotics unless there is severe distress or danger; if needed, use the lowest dose and stop within days (quetiapine 12.5 to 25 mg in Lewy body dementia or Parkinson disease). Do not give anticholinergics or benzodiazepines. Cholinesterase inhibitors are not started to treat delirium.

Monitoring. Recovery of baseline cognition over weeks, and risk of relapse.