Psychiatry of Old Age: Distinguishing Delirium, Dementia, and Depression
Core concepts
Older adults present atypically: depression may manifest as somatic complaints or pseudodementia; delirium is acute, fluctuating, with impaired attention and altered consciousness; dementia is chronic, progressive cognitive decline with preserved consciousness until late. Know the common dementias: Alzheimer's (insidious memory decline), vascular (stepwise, focal deficits), Lewy body (fluctuations, visual hallucinations, parkinsonism), and frontotemporal (behavioural or language variants). Understand the risks of polypharmacy, anticholinergic burden, falls, and the interaction of physical illness with mental state.
Traps
Questions often test whether a presentation is delirium superimposed on dementia, or depression mimicking dementia. Be cautious with capacity assessments, and remember that depression with cognitive impairment may improve with treatment, whereas dementia does not.
Worked example
An 82-year-old becomes acutely confused after starting a new sedative, with fluctuating attention and visual hallucinations. The rule of thumb: delirium is a medical emergency; identify and treat the underlying cause (infection, drugs, metabolic disturbance) and avoid attributing acute confusion to dementia alone.
Key points for revision
Acute fluctuating confusion is delirium until proven otherwise.