Which symptom most distinguishes delirium from dementia?

• A. Gradual memory loss
• B. Slow progression
• C. Acute onset with fluctuating attention
• D. Chronic confusion

Answer: (C)

Delirium is defined by an abrupt, acute change in mental status with disturbances in attention and awareness that tend to fluctuate over hours to days. That fluctuation in attention is what most clearly separates delirium from dementia, which develops gradually with a steady, chronic decline in memory and other cognitive functions while attention remains relatively preserved early on. So the hallmark feature here is an acute onset coupled with fluctuating attention. The other descriptions—gradual memory loss, slow progression, and chronic confusion—fit dementia, not delirium, and remind us that delirium requires prompt identification to find and treat the underlying cause.