Causes of delirium in older people often include less severe conditions: Dehydration A nonneurologic disorder (eg, urinary tract infection, influenza, thiamin deficiency, vitamin B12 deficiency) Pain Urinary retention or severe constipation Sensory deprivation Sleep deprivation Stress (any type) Use of a bladder catheter Certain age-related changes make older people more susceptible to developing delirium: An increased sensitivity to drugs (particularly sedatives, anticholinergics, and antihistamines) Changes in the brain (eg, atrophy, lower levels of acetylcholine) The presence of conditions that increase the risk of delirium (eg, stroke, dementia, Parkinson disease, other neurodegenerative disorders, polypharmacy, dehydrations, undernutrition, immobility) The most obvious symptom of delirium, confusion, may be harder to recognize in older people.