Full Definition

Delirium is an acute neuropsychiatric syndrome characterized by sudden onset of confusion, disorganized thinking, and fluctuating attention. Unlike dementia, which develops gradually over months to years, delirium develops over hours to days and is almost always caused by an identifiable medical problem.

Common causes in older adults include urinary tract infections, pneumonia, medication side effects or polypharmacy, dehydration, pain, sleep deprivation, surgery, and the unfamiliar and stressful environment of a hospital. Older adults with existing dementia are particularly vulnerable to developing superimposed delirium.

Delirium has two main presentations: hyperactive (agitation, combativeness, pulling at tubes — the most recognized form) and hypoactive (withdrawal, lethargy, reduced responsiveness — often mistaken for depression or “just getting older”). Hypoactive delirium is more common in elderly patients and frequently missed by clinical teams.

For families, delirium during a hospital stay is alarming and disorienting. It is essential to understand that delirium is not the same as dementia — it is usually reversible if the underlying cause is treated. However, episodes of delirium can accelerate cognitive and functional decline in older adults, particularly those with pre-existing dementia. Good delirium prevention — keeping patients mobile, oriented, with adequate sleep and nutrition — is a hallmark of quality hospital care.