The definition of delirium previously had been considered in simplified terms as an acute confusional state. However, since the 1980s, it has been refined, whereby earlier versions of the Diagnostic and Statistical Manual of Mental Disorders (DSM) were more weighted upon the causes of generalized brain dysfunction than stratification of clinical constructs that define the disorder [12]. The construct and definition of delirium continues to evolve with the recent revision of the DSM [13]; the DSM-5 avoids the term “consciousness” and more restrictively defines delirium in terms of cognitive impairment and inattention with less emphasis on the level of arousal. The DSM-5 criteria (Table 7.4) also take into account established or preexisting neurocognitive disorders. In addition, DSM-5 criteria consider the context of acute cognitive impairment and fluctuation in relation to an individual’s baseline

Table 7.2 Characteristic clinical features of delirium and dementia





Clinical features


Sudden, with identifiable time of onset

Slow and gradual, with an uncertain beginning and changes noted over months


Days to weeks, although it may be longer (persistent)

At least 6 months of cognitive impairment


Almost always another condition (e.g., infection, dehydration, change in environment, brain hemorrhage, use or withdrawal of certain drugs). Note in 25 % of cases causes may not be found

Usually a chronic brain disorder (e.g., Alzheimer’s disease, Lewy body dementia, vascular dementia, etc.)


Usually reversible. In some occasions, a prolonged course (e.g., persistent delirium)

Progressive, irreversible

Diurnal variation

Almost always worse at nighttime (day-night reversal)

Often worse at latter part of the afternoon and nighttime (known as sundowning effect), especially in vascular and mixed dementia

Need for medical attention

Urgent to prevent dire consequences

Required but less urgently

Neuropsychiatric features


Severely impaired (cardinal feature)

Unimpaired until dementia becomes severe

Level of consciousness

Impaired and fluctuating, ranging from lethargic to hyperalert

Unimpaired until late stages



Increased or decreased

Often normal

Use of language

Slow, often incoherent, and inappropriate

Occasional word finding difficulties that can become more apparent with time, e.g., semantic (category) and phonemic (word) dysfluency



Significantly impaired, especially for recent events (working memory) often preceding the impaired long-term memory

function. However, differences between DSM-5 and DSM-IV criteria have raised concerns of the sensitivity of detecting delirium based on the revised criteria [14]. Hence, recommendation for broader inclusion to include individuals with cognitive impairment secondary to impaired arousal (e.g., drowsiness, obtundation, stupor) as well as consistent interpretation of criteria is thought to be important factors especially with regard to patient safety as the over-detection of delirium is thought to be more beneficial when juxtaposed with under-detection [14,15].

Table 7.3 Risk factors for delirium and dementia [11]





Preexisting brain disease (e.g., dementia, head injury, brain metastasis, vascular incidents)

Head injury

Medication (e.g., anticholinergics, benzodiazepine, opioids)

Cumulative use of anticholinergic medication (e.g., tricyclic antidepressants, first-generation antihistamines, and bladder antimuscarinics [11])

Various medical conditions (e.g., electrolyte disorders, dehydration, infection, injury, pain, metabolic disorders, etc.)

Cardiovascular and cerebrovascular illnesses

Surgical interventions (e.g., heart surgery, organ transplant, hip fractures)

Metabolic syndrome

Unfamiliar environment; changes in environment and number of interventions

Increase in alcohol intake

A variation in the SLC6A3 gene and possibly the DRD2 gene may protect from delirium

Multiple genetic causes (e.g., mutations at Chr 1, Chr 14, and Chr 21 for early-onset AD; SNCA triplication and GBA mutation for Lewy body dementia; H1/H1 haplotype; ApoE e4 allele for AD, VaD, and DLB; Chr 21 trisomy (Down’s syndrome)

No convincing evidence for APoE as a risk factor

Sensory deprivation (e.g., poor eyesight and hearing)

Poor education

Table 7.4 DSM-5 criteria for delirium

A. A disturbance in attention (i.e., reduced ability to direct, focus, sustain, and shift attention) and awareness (reduced orientation to the environment)

B. The disturbance develops over a short period of time (usually hours to a few days), represents a change from baseline attention and awareness, and tends to fluctuate in severity during the course of a day

C. An additional disturbance in cognition (e.g., memory deficit, disorientation, language, visuospatial ability, or perception)

D. The disturbances in Criteria A and C are not better explained by a preexisting, established, or evolving neurocognitive disorder and do not occur in the context of a severely reduced level of arousal, such as coma

E. There is evidence from the history, physical examination, or laboratory findings that the disturbance is a direct physiological consequence of another medical condition, substance intoxication or withdrawal, or exposure to a toxin or is due to multiple etiologies

Adapted from DSM-5 [13]. DSM-5, Diagnostic and Statistical Manual, Fifth edition

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