Delirium vs Dementia vs Depression — The 3 D's

Delirium is acute, reversible, and a medical emergency. It develops over hours to days, fluctuates throughout the day (often worse at night), and the hallmark is disturbed attention and consciousness. The client cannot focus, is easily distracted, and may have visual hallucinations. Always assume delirium has an underlying medical cause: infection (UTI is the classic culprit in older adults), medication toxicity, dehydration, hypoxia, or metabolic imbalance. Treat the cause, and delirium resolves. Dementia is chronic, progressive, and irreversible. Onset is insidious over months to years. Memory loss — especially recent memory — is the hallmark, while attention and consciousness remain intact until late stages. The client may confabulate to fill memory gaps. Orientation deteriorates in a predictable order: time first, then place, then person last. Sundowning (worsening confusion in the evening/night) is classically associated with dementia but can also occur in delirium. Depression can mimic dementia ("pseudodementia") in older adults with slowed cognition, poor concentration, and apparent memory loss. The critical difference: depressed clients often say "I don't know" when tested, whereas dementia clients genuinely try but give wrong answers. Depression has a relatively identifiable onset, often linked to a loss or life change, and responds to treatment.