A 72-year-old woman is admitted to the ICU with acute confusion, disorientation, and visual hallucinations that developed over 6 hours. She has a fever of 38.5°C, recent urinary symptoms, and elevated WBC. Her family reports she was cognitively intact 24 hours ago. What is the most common cause of delirium in this hospitalized elderly patient?

## Most Common Cause of Delirium in Elderly Hospitalized Patients **Key Point:** Infection (particularly urinary tract infection and sepsis) is the most common reversible cause of delirium in elderly hospitalized patients, accounting for 30–40% of delirium cases. ### Delirium Etiology Hierarchy in Hospitalized Elderly ```mermaid flowchart TD A[Acute Delirium in Elderly]:::outcome --> B{Cause?}:::decision B -->|Infection/Sepsis| C[UTI, Pneumonia, Intra-abdominal]:::action B -->|Medications| D[Opioids, Anticholinergics, Benzos]:::action B -->|Metabolic| E[Hypoglycemia, Hyponatremia, Hypoxia]:::action B -->|CNS| F[Stroke, ICH, Seizure]:::urgent C --> G[Most Common 30-40%]:::outcome D --> H[Second Most Common 15-20%]:::outcome E --> I[Common 20-30%]:::outcome F --> J[Less Common 5-10%]:::outcome ``` **High-Yield:** The mnemonic **DELIRIUM** captures common causes: - **D**rugs (medications) - **E**lectrolytes (metabolic derangements) - **L**ung/Liver disease (hypoxia, hepatic encephalopathy) - **I**nfection (UTI, pneumonia, sepsis) ← **MOST COMMON** - **R**enal failure - **I**ntracranial pathology - **U**reteral/Urinary retention - **M**yocardial infarction ### Why Infection is Most Common in This Case | Clinical Feature | Supports Infection/Sepsis | | --- | --- | | **Fever (38.5°C)** | ✓ Systemic inflammatory response | | **Acute onset (6 hours)** | ✓ Infection-induced delirium is acute | | **Urinary symptoms** | ✓ UTI is the most common source in elderly | | **Elevated WBC** | ✓ Leukocytosis indicates infection | | **Prior cognitive intactness** | ✓ Delirium, not dementia (reversible) | | **Visual hallucinations** | ✓ Common in sepsis-induced delirium | **Clinical Pearl:** In elderly patients, UTI often presents *atypically* without dysuria or frequency—delirium and fever may be the only signs. Urosepsis is a leading cause of preventable delirium in hospitalized elderly. ### Key Distinction: Delirium vs Dementia | Feature | Delirium | Dementia | | --- | --- | --- | | **Onset** | Acute (hours to days) | Insidious (months to years) | | **Course** | Fluctuating, waxing-waning | Gradual, progressive | | **Consciousness** | Altered (hyperalert or hypoalert) | Preserved until late | | **Reversibility** | Often reversible | Usually irreversible | | **Common cause** | Infection, drugs, metabolic | Neurodegeneration | | **Most common cause** | **Infection** | **Alzheimer's disease** | **Key Point:** The acute 6-hour onset with fever and infection markers makes this **delirium secondary to infection**, not dementia. Infection is the single most common reversible cause of delirium in hospitalized elderly. [cite:Harrison 21e Ch 435]