What are the definitions, causes, and major clinical features of delirium and chronic confusional states?

Delirium and Chronic Confusional States: Definitions, Causes, and Clinical Features

Delirium Definition

Delirium is an acute disorder of cognition and attention characterized by acute onset (hours to days), fluctuating course, inattention, impaired level of consciousness, and disorganized thinking—representing a medical emergency that can be fatal if untreated. 1

• Delirium is also known as encephalopathy, confusional state, or altered mental status 1
• It is a sometimes life-threatening but often preventable clinical syndrome, especially common in older vulnerable adults 1
• The syndrome represents acute brain failure or acute encephalopathy 2

Major Clinical Features of Delirium

Core Diagnostic Features

• Acute onset and fluctuating course: Symptoms develop over hours to days and fluctuate within minutes to hours throughout the day 1
• Inattention: Reduced awareness of surroundings, difficulty focusing, easily distracted, withdrawal or absence of response 1
• Impaired level of consciousness: Altered awareness ranging from hyperalert to stuporous 1
• Cognitive disorganization: Disorientation, memory impairment, altered language, rambling or nonsense speech 1

Supportive Clinical Features

• Sleep-wake cycle disturbances: Disrupted circadian rhythm, often worsening at night 1
• Perceptual disturbances: Visual hallucinations, misperceptions, delusions 1
• Behavioral changes: Inappropriate or unsafe behavior, emotional lability, anxiety, fear 1
• Psychomotor changes: Variable activity levels depending on subtype 1

Three Major Subtypes

Hyperactive delirium (more obvious but less common):

• Restlessness, agitation, constant movement 1
• Screaming, combative behavior 3

Hypoactive delirium (frequently missed but more common):

• Paucity of speech, slow or no movement, unresponsiveness 1
• Quiet, inactive, stuporous appearance 3
• Associated with greater risk of morbidity and mortality 1, 4

Mixed delirium:

• Switching between hyperactive and hypoactive features 1

Causes of Delirium

Common Precipitating Factors

• Infections: Any acute infection, particularly common in hospitalized patients 1, 3
• Toxic-metabolic disorders: Electrolyte disturbances, organ failure, hypoxia 1
• Medications: Drugs with anticholinergic properties, sedatives, opioids 1, 3
• Hydration disturbances: Dehydration or fluid overload 1
• Postoperative state: Occurs in >20% of high-risk patients following major surgery 1

High-Risk Clinical Settings

• General medicine wards: ~20% of older patients 1
• Post-surgical patients: >20% of high-risk cases 1
• Intensive care units: 50-70% of mechanically ventilated patients 1

Chronic Confusional States (Dementia)

Chronic confusional states refer to dementia—an insidious, chronic, and progressive loss of previously acquired cognitive abilities, fundamentally distinct from delirium in time course and reversibility. 5, 6

Definition and Distinction from Delirium

• Dementia develops gradually over months to years, not hours to days 5, 6
• Cognitive decline is progressive and generally irreversible, unlike delirium which is potentially reversible 5, 6
• Level of consciousness typically remains normal until advanced stages, contrasting with delirium's altered consciousness 1, 7
• Attention is relatively preserved early in dementia, whereas inattention is a cardinal feature of delirium 7, 6

Major Clinical Features of Dementia

• Memory impairment: Progressive loss of short-term and eventually long-term memory 5, 6
• Executive dysfunction: Impaired planning, organization, and judgment 5
• Language difficulties: Word-finding problems, comprehension deficits 5
• Functional decline: Gradual loss of ability to perform activities of daily living 5, 6
• Behavioral changes: Personality changes, apathy, or disinhibition developing over time 5

Causes of Dementia (Chronic Confusional States)

• Alzheimer's disease: Most common neurodegenerative cause 1
• Vascular cognitive impairment: Stroke-related or chronic small vessel disease 1
• Lewy body dementia: Associated with Parkinson's disease features 4
• Frontotemporal dementia: Behavioral and language variants 5
• Mixed pathologies: Combination of neurodegenerative processes 1, 5

Critical Interrelationship Between Delirium and Dementia

Patients with dementia have substantially higher risk of developing delirium, and delirium itself is an independent risk factor for subsequent dementia development. 5, 6

Key Clinical Implications

• Delirium superimposed on dementia leads to accelerated cognitive decline, increased length of hospital stay, higher rates of rehospitalization, institutionalization, and death 1
• Delirium may represent a modifiable risk factor for dementia, making prevention strategies critically important 1, 5
• When delirium occurs in someone with pre-existing dementia, it represents a medical emergency with devastating prognostic implications 1

Diagnostic Approach

For Delirium

• Establish baseline cognitive function through knowledgeable informant interview to determine time course and trajectory of changes 1
• Use validated assessment tools: Confusion Assessment Method (CAM) or similar instruments 1, 4
• Perform repeated assessments throughout the day due to fluctuating nature 1
• Obtain appropriate laboratory studies to identify underlying causes: complete metabolic panel, complete blood count, urinalysis, chest radiograph 1
• Consider EEG to rule out non-convulsive status epilepticus, which can mimic delirium 1, 4, 8

For Dementia

• Gradual onset over months to years distinguishes from delirium's acute presentation 5, 7, 6
• Cognitive testing shows deficits but without fluctuations in attention or consciousness 7, 6
• Neuroimaging may show atrophy or vascular changes consistent with chronic process 8

Common Pitfalls

• Hypoactive delirium is frequently missed because patients appear quiet and withdrawn rather than agitated 1, 4
• Assuming confusion in elderly patients is "just dementia" without assessing for acute changes suggesting delirium 1, 5
• Failing to recognize delirium in patients with pre-existing dementia, missing the acute-on-chronic presentation 1, 5
• Not obtaining collateral history to establish baseline cognitive function and identify acute changes 1, 7
• Using terms like "encephalopathy" when multifactorial delirium is present, potentially causing clinicians to overlook reversible causes 1, 8