What features distinguish delirium from dementia?
Although this distinction cannot always be made with certainty, several features are helpful.
Sudden onset suggests delirium, as do findings of altered consciousness, marked problems with attention and concentration out of proportion to other deficits, cognitive fluctuations (e.g., lucid intervals), psychomotor and/or autonomic overactivity, fragmented speech, and marked hallucinations (especially auditory or tactile).
Chronically demented patients may develop delirium in addition to dementia, which will change the clinical picture.