The nature and degree of impairment are variable and often depend on the particular social setting of the individual. For example, mild cognitive impairment may significantly impair an individual's ability to perform a complex job but not a less demanding one. Some individuals with dementia show disinhibited behavior, including making inappropriate jokes, neglecting personal hygiene, exhibiting undue familiarity with strangers, or disregarding conventional rules of social conduct. Occasionally, they may harm others by striking out. 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.