|An etiologically nonspecific
syndrome characterized by concurrent disturbances of
consciousness and attention, perception, thinking,
memory, psychomotor behaviour, emotion, and the sleep-wake
cycle. It may occur at any age but is most common after
the age of 60 years. The delirious state is transient and
of fluctuating intensity; most cases recover within 4
weeks or less. However, delirium lasting, with
fluctuations, for up to 6 months is not uncommon,
especially when arising in the course of chronic liver
disease, carcinoma, or subacute bacterial endocarditis.
The distinction that is sometimes made between acute and
subacute delirium is of little clinical relevance; the
condition should be seen as a unitary syndrome of
variable duration and severity ranging from mild to very
severe. A delirious state may be superimposed on, or
progress into, dementia.
This category should not be used for states of delirium associated with the use of psychoactive drugs specified in F10-F19. Delirious states due to prescribed medication (such as acute confusional states in elderly patients due to antidepressants) should be coded here. In such cases, the medication concerned should also be recorded by means of an additional T code from Chapter XIX of ICD-10.
For a definite diagnosis, symptoms, mild or severe, should be present in each one of the following areas:
(a) impairment of consciousness and attention (on a continuum from clouding to coma; reduced ability to direct, focus, sustain, and shift attention);
(b) global disturbance of cognition (perceptual distortions, illusions and hallucinations - most often visual; impairment of abstract thinking and comprehension, with or without transient delusions, but typically with some degree of incoherence; impairment of immediate recall and of recent memory but with relatively intact remote memory; disorientation for time as well as, in more severe cases, for place and person);
(c) psychomotor disturbances (hypo- or hyperactivity and unpredictable shifts from one to the other; increased reaction time; increased or decreased flow of speech; enhanced startle reaction);
(d) disturbance of the sleep-wake cycle (insomnia or, in severe cases, total sleep loss or reversal of the sleep-wake cycle; daytime drowsiness; nocturnal worsening of symptoms; disturbing dreams or nightmares, which may continue as hallucinations after awakening);
(e) emotional disturbances, e.g. depression, anxiety or fear, irritability, euphoria, apathy, or wondering perplexity.
The onset is usually rapid, the course diurnally fluctuating, and the total duration of the condition less than 6 months. The above clinical picture is so characteristic that a fairly confident diagnosis of delirium can be made even if the underlying cause is not clearly established. In addition to a history of an underlying physical or brain disease, evidence of cerebral dysfunction (e.g. an abnormal electroencephalogram, usually but not invariably showing a slowing of the background activity) may be required if the diagnosis is in doubt.