Delirium

Definition

Delirium is an acute, transient, usually reversible and fluctuating disturbance of attention, cognition and level of consciousness. Synonyms are acute confusional state and toxic-metabolic encephalopathy.

Diagnostic criteria according to DSM-5-TR:

• disturbance in attention (e.g. difficulty focusing or following what is said) and awareness of the environment (reduced orientation)
• development over a short period (hours to days) with fluctuation during the day
• acute change in cognition (e.g. memory, language, perception, thinking)
• evidence from the history, examination or laboratory tests that a medical condition, a substance (including drugs and toxins) or substance abstinence is the cause

Classification

By psychomotor presentation, the following are distinguished:

• hyperactive delirium: irritable, agitated, hyperactive and hyperalert
• hypoactive delirium: quiet, reclusive and lethargic; common in very old people and easily mistaken for depression
• mixed delirium: alternating between agitation and reclusiveness

Delirium in pre-existing dementia is called delirium superimposed on dementia.

Occurrence & epidemiology

Delirium can occur at any age but is much more common in older people. At least 10 % of people over 65 have delirium on arrival in hospital, and 15–50 % develop it during the hospital stay – particularly often after surgery and in critically ill people. It is also common in nursing homes. In people with dementia, delirium occurs in up to 49 % during a hospital stay. In younger people, delirium is usually caused by recreational drugs, medicines or a life-threatening systemic illness.

Aetiopathogenesis

The most common causes are medicines (especially anticholinergic substances, opioids and other psychoactive agents), dehydration and infections. Predisposing and precipitating factors usually act together; sometimes no cause is found.

• Predisposing factors: brain disorders (e.g. dementia, stroke, Parkinson's disease), advanced age, impaired vision or hearing, alcohol intoxication, multiple coexisting disorders
• Precipitating factors: new medicines (especially 3 or more), infections (e.g. urinary tract infection), dehydration, shock, hypoxia, anemia, immobility, undernutrition, bladder catheters, hospital stay, pain, sleep deprivation, emotional stress, recent anesthesia; unrecognized liver or kidney failure can delay the clearance of previously well-tolerated medicines
• Neurological causes: stroke and TIA, encephalitis and meningitis, non-convulsive status epilepticus and postictal state, head injury and subdural hematoma, brain tumors
• Metabolic and endocrine: electrolyte disorders (e.g. hyponatremia, hypernatremia, hypercalcemia), hypo- and hyperglycemia, hepatic or uremic encephalopathy, Wernicke encephalopathy, thyroid and adrenal disorders, thiamine or vitamin B12 deficiency
• Abstinence syndromes: alcohol, benzodiazepines, barbiturates, opioids

Pathophysiologically, a reversible disturbance of cerebral oxidative metabolism, abnormalities of several neurotransmitters (above all a cholinergic deficit) and inflammatory mediators are assumed. Older people are particularly vulnerable to reduced cholinergic transmission.

Clinical features

• Inattention as the core symptom: difficulty focusing, maintaining or shifting attention
• fluctuating level of consciousness; disorientation to time, sometimes also to place or person
• hallucinations, delusions and paranoia
• disorganized thinking and disordered speech (slurred, rapid, neologisms, chaotic)
• changes in personality and mood, inappropriate behavior, fearfulness
• fluctuations over minutes to hours, often less during the day and worse at night
• grossly distorted sleep-wake and eating patterns
• impaired insight and judgement

Unlike dementia, delirium mainly affects attention, begins acutely and is often reversible.

Diagnosis

Delirium is often overlooked, especially in older people. The diagnosis is clinical.

• Testing attention as the first step: e.g. immediate repetition of three words, digit span (7 digits forwards, 5 backwards), days of the week forwards and backwards
• Standardised criteria: DSM-5-TR or the Confusion Assessment Method (CAM)
• Collateral history: relatives and carers clarify whether the change is new and distinct from any pre-existing dementia
• Physical examination: vital signs, hydration status, sources of infection, skin, head and neck, neurological findings; fever and meningism suggest CNS infection, tremor and myoclonus suggest uremia, liver failure, intoxication or electrolyte disorders, ophthalmoplegia and ataxia suggest Wernicke encephalopathy, focal deficits suggest a structural brain lesion
• Basic work-up: CT or MRI of the head, full blood count, blood cultures, chest X-ray, urinalysis, pulse oximetry or blood gas analysis, electrolytes, urea, creatinine, glucose, levels of suspected medicines, urine drug screen
• Extended work-up: liver tests, calcium and albumin, TSH, vitamin B12, ESR/CRP, ANA, syphilis serology; if needed, cerebrospinal fluid analysis (meningitis, encephalitis, subarachnoid hemorrhage), ammonia, heavy metals; EEG if non-convulsive status epilepticus is suspected

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Further reading (open access)

1. MSD Manual Professional: Delirium
2. StatPearls: Delirium

Cross-references