What is delirium?

Delirium Definition

Delirium is an acute confusional state characterized by disturbed attention, awareness, and cognition that develops rapidly (within hours to days), fluctuates throughout the day, and cannot be better explained by a pre-existing neurocognitive disorder. 1

Core Features of Delirium

Delirium is defined by three primary features:

1. Disturbed attention and awareness:

   • Difficulty focusing or maintaining attention
   • Easily distracted
   • Frequent topic changes during conversation
   • Withdrawal or absence of response to surroundings 1

2. Cognitive impairment:

   • Disorientation to time, place, or person
   • Memory deficits, particularly recent events
   • Disorganized thinking and speech patterns
   • Impaired reasoning and judgment 1

3. Acute onset and fluctuating course:

   • Develops rapidly (hours to days)
   • Symptoms often worsen in the evening ("sundowning")
   • Severity fluctuates throughout the day with potential lucid intervals 1

Delirium Subtypes

Delirium presents in three distinct clinical subtypes:

1. Hyperactive delirium:

   • Characterized by restlessness, agitation, and increased psychomotor activity
   • Enhanced startle reaction
   • Increased flow of speech
   • More easily recognized clinically 1

2. Hypoactive delirium:

   • Characterized by lethargy, reduced movement, and decreased responsiveness
   • Reduced speech and psychomotor activity
   • Often missed or misdiagnosed despite being more common 1

3. Mixed delirium:

   • Fluctuation between hyperactive and hypoactive features
   • Unpredictable presentation 1

Clinical Impact and Epidemiology

Delirium is highly prevalent in healthcare settings:

• Affects approximately 20% of older patients on general medicine wards
• Present in >20% of high-risk patients after major surgery
• Occurs in 50-70% of mechanically ventilated ICU patients 1

The consequences of delirium are severe:

• Increased length of hospital stay
• Higher morbidity and mortality rates
• Greater risk of institutionalization
• Accelerated cognitive decline and increased risk of dementia
• Significant healthcare costs ($143-152 billion annually in the US) 1

Diagnostic Approach

Delirium is a clinical diagnosis requiring:

1. Validated assessment tools:

   • Confusion Assessment Method (CAM)
   • Richmond Agitation Sedation Scale
   • Delirium Rating Scale 1

2. Collateral history:

   • Information from family members about baseline cognitive function
   • Timeline of symptom development 1

3. Exclusion of other causes:

   • Differentiation from primary psychiatric disorders
   • Ruling out pre-existing dementia 1, 2

Common Pitfalls in Delirium Recognition

1. Missing hypoactive delirium: The quiet, withdrawn presentation is frequently overlooked, despite being more common than hyperactive delirium 1

2. Confusing delirium with dementia: Unlike dementia, delirium has an acute onset, fluctuating course, and is potentially reversible 1, 2

3. Failing to recognize mixed presentations: The fluctuation between hyperactive and hypoactive states can lead to inconsistent assessment 1

4. Overlooking delirium in patients with pre-existing cognitive impairment: Delirium superimposed on dementia is particularly challenging to diagnose 1

5. Attributing symptoms solely to psychiatric conditions: Delirium should be considered a medical emergency with underlying physiological causes 1, 2

By recognizing delirium promptly and addressing its underlying causes, clinicians can significantly improve patient outcomes and reduce the substantial morbidity, mortality, and healthcare costs associated with this condition.