A 72-year-old woman with hypertension and diabetes mellitus is admitted to the hospital with acute-onset confusion, disorientation, and agitation that developed over 6 hours. She has a fever of 38.5°C, tachycardia, and a urinary catheter in place for 3 days. Her mini-mental state examination score is 18/30. What is the most common cause of delirium in this hospitalized elderly patient?

## Most Common Cause of Delirium in Hospitalized Elderly **Key Point:** Infection (especially urinary tract infection and sepsis) is the single most common reversible cause of delirium in hospitalized elderly patients, accounting for 30–40% of delirium cases. ### Clinical Context: Risk Factors in This Patient **High-Yield:** The patient has multiple delirium risk factors: - Advanced age (72 years) - Comorbidities (hypertension, diabetes) - Acute fever and tachycardia (signs of infection) - Indwelling urinary catheter for 3 days (major UTI risk) - Acute-onset confusion over 6 hours (typical delirium timeline) ### Delirium vs Dementia: Key Distinctions | Feature | Delirium | Dementia | | --- | --- | --- | | **Onset** | Acute (hours to days) | Insidious (months to years) | | **Course** | Fluctuating, waxing-waning | Gradual, progressive | | **Consciousness** | Altered (hyperalert or lethargic) | Normal | | **Attention** | Severely impaired | Relatively preserved early | | **Reversibility** | Often reversible if cause treated | Usually irreversible | | **Common Causes** | Infection, drugs, metabolic, hypoxia | Alzheimer's, vascular, Lewy body | | **Mortality** | High if untreated | Chronic decline | ### Most Common Causes of Delirium (Mnemonic: DELIRIUM) **Mnemonic:** **D**rugs (anticholinergics, benzodiazepines, opioids), **E**lectrolyte imbalance, **L**ack of drugs (alcohol/benzodiazepine withdrawal), **I**nfection (UTI, pneumonia, sepsis), **R**enal/Respiratory failure, **I**ntracranial (stroke, hemorrhage), **U**reteral (urinary retention), **M**etabolic (hypoglycemia, hypoxia) **Clinical Pearl:** In hospitalized elderly patients, infection (especially UTI) is the leading cause because: 1. Elderly patients often present atypically with infection (no dysuria, no frequency) 2. Indwelling catheters increase UTI risk exponentially 3. Sepsis from UTI can rapidly cause delirium without localizing symptoms 4. The acute presentation and fever in this case are classic for sepsis-induced delirium ### Why Infection is Most Common in This Case 1. **Fever + tachycardia** = systemic inflammatory response 2. **Urinary catheter for 3 days** = high risk for bacteriuria and UTI 3. **Elderly + comorbidities** = impaired immune response, atypical presentation 4. **Acute onset over 6 hours** = consistent with acute infection/sepsis 5. **Reversibility potential** = treating the infection often rapidly improves mental status **High-Yield:** Always check urinalysis, urine culture, blood cultures, and CBC in any elderly hospitalized patient with acute delirium. UTI is often the culprit even without classic urinary symptoms. [cite:Harrison 21e Ch 28]