Depressed mood, with or without neurovegetative changes, is quite common, as are sleep disturbances independent of depression. Hallucinations can occur in all sensory modalities, but visual hallucinations are most common. Delirium is frequently superimposed on dementia because the underlying brain disease increases susceptibility to the effects of medications or concurrent general medical conditions. Dementia is sometimes accompanied by motor disturbances, which may include gait difficulties, slurred speech, and a variety of abnormal movements. Other neurological symptoms, such as myoclonus and seizures, may also occur.
Memory impairment occurs in both delirium and dementia.
Delirium is also characterized by a reduced ability to maintain and shift attention appropriately, but the cognitive deficits tend to fluctuate, while those of dementia tend to be stable or progressive. An amnestic disorder is characterized by memory impairment without significant impairment in other cognitive domains. Mental retardation has an onset before age 18 and is characterized by significantly subaverage general intellectual functioning, which does not necessarily include memory impairment. Schizophrenia may be associated with multiple cognitive impairments and a decline in functioning, but the cognitive impairment tends to be less severe and occurs against a background of psychotic and behavioral symptoms meeting the established diagnostic criteria. The two may sometimes be distinguished on the basis of an assessment of the course and onset of depressive and cognitive symptoms and by response to treatment of the depression.