Thinking is disorganized resulting in incoherent or rambling speech, and memory is impaired. Disorientation to time and place follows, but disorientation to person is rarely seen. M any patients describe persecutory delusions, suspiciousness, bizarre thoughts and images, and loose associations. Perceptual abnormalities may include distortions, illusions, or frank hallucinations. Visual illusions and hallucinations are most common, followed in frequency by auditory and tactile illusions.
Hallucinations occur less frequently in the elderly than in middle-aged persons.
P hysicians frequently mistake delirium for dementia. Whereas, with rare exception, dementia presents insidiously, delirium presents as an acute loss of global cognitive function in the setting of an acute medical or surgical illness . Distinguishing dementia from delirium superimposed on dementia requires knowledge of the patients prior cognitive function. The delirious patient with no history of dementia manifests new cognitive deficits, whereas delirious patients with a prior dementia demonstrates a manifests a worsening of baseline cognitive dysfunction. If present, lethargy or stupor always indicate delirium, as these physical signs are not manifestations of dementia.