600 Neurocognitive Disorders
condition, or multiple etiologi es). Delirium often occurs in  the context of an underlying
NCD. The impaired brain function of individuals with mild and major NCD renders them
more vulnerable to delirium.
There is an accompanying change in at le ast one other area that may include memory
and learning (particularly recent memory), diso rientation (particularly to time and place),
alteration in language, or perceptual distorti on or a perceptual-motor disturbance (Crite-
rion C). The perceptual dist urbances accompanying delirium include misinterpretations,
illusions, or hallucinations; these disturbances are typically visual, but may occur in other
modalities as well, and range from simple an d uniform to highly complex. Normal atten-
tion/arousal, delirium, and coma lie on a cont inuum, with coma defined as the lack of any
response to verbal stimuli. The ability to evaluate cognition to diagnose delirium depends
on there being a level of arousal sufficient for response to verbal stim ulation; hence, delir-
ium should not be diagnosed in the context of coma (Criterion D). Many noncomatose pa-
tients have a reduced level of arousal. Those patients who show only minimal responses to
verbal stimulation are incapable of engaging with attempts at standardized testing or even
interview. This inability to engage should be  classified as severe inattention. Low-arousal
states (of acute onset) should be recognized as indicating severe inattention and cognitive
change, and hence delirium. They are clinically indistinguishable from delirium diag-
nosed on the basis of inattentio n or cognitive change elicited through cognitive testing and
interview. 
Associated Features Supporting Diagnosis