A 72-year-old man with a 3-year history of progressive memory loss and difficulty with activities of daily living is brought to the emergency department by his son. Over the past 6 hours, the patient has become acutely confused, agitated, and is seeing insects crawling on his skin. His temperature is 38.5°C, heart rate 110/min, and blood pressure 145/90 mmHg. Urinalysis shows pyuria and nitrites. The son reports that the patient was relatively stable yesterday. What is the most likely diagnosis?

Explanation

## Clinical Presentation Analysis **Key Point:** This patient presents with a **pre-existing dementia** (3-year progressive memory loss) complicated by an **acute change in mental status** over hours, with fever, tachycardia, and urinary tract infection findings. ## Delirium Superimposed on Dementia ### Diagnostic Features Present - **Acute onset** (6 hours) — hallmark of delirium - **Fluctuating consciousness** — agitation, visual hallucinations (insects) - **Identifiable precipitant** — urinary tract infection (pyuria, nitrites, fever) - **Baseline cognitive impairment** — 3-year dementia history - **Autonomic instability** — tachycardia, hypertension, fever **High-Yield:** Delirium is a medical emergency superimposed on chronic cognitive decline. The presence of an acute medical stressor (UTI) in a dementia patient is the classic presentation. ## Delirium vs Dementia: Key Distinctions | Feature | Delirium | Dementia | |---------|----------|----------| | **Onset** | Acute (hours to days) | Insidious (months to years) | | **Course** | Fluctuating throughout day | Slowly progressive | | **Consciousness** | Altered (hypoactive, hyperactive, mixed) | Usually normal early | | **Attention** | Severely impaired | Relatively preserved early | | **Hallucinations** | Common (visual, tactile) | Less common, late stage | | **Reversibility** | Often reversible if cause treated | Usually irreversible | | **Cause** | Medical/surgical/toxic | Neurodegenerative | **Clinical Pearl:** In elderly patients, delirium is often mistaken for dementia progression. Always ask: "Was this change acute?" If yes, think delirium and search for the precipitant (infection, medication, metabolic derangement, hypoxia). ## Management Algorithm ```mermaid flowchart TD A[Elderly patient with acute confusion]:::outcome --> B{Baseline cognitive status?}:::decision B -->|Normal baseline| C[Delirium until proven otherwise]:::action B -->|Known dementia| D[Delirium superimposed on dementia]:::action D --> E[Identify precipitant]:::action E --> F[Treat UTI with antibiotics]:::action E --> G[Correct metabolic abnormalities]:::action E --> H[Review medications]:::action F --> I[Resolution of acute confusion]:::outcome ``` **Mnemonic:** **I WATCH DEATH** — causes of delirium - **I**nfection (UTI, pneumonia, sepsis) - **W**ithdrawal (alcohol, benzodiazepines) - **A**cute metabolic (electrolytes, glucose, renal/hepatic failure) - **T**oxins (medications, drugs) - **C**NS pathology (stroke, seizure, intracranial hemorrhage) - **H**ypoxia (cardiac, respiratory) - **D**eficiencies (thiamine, B12) - **E**ndocrinopathy (thyroid, adrenal) - **A**rrhythmias (cardiac) - **T**emperature (fever, hypothermia) - **H**eavy metals **High-Yield:** In this case, the UTI is the precipitant. Treatment of the infection will reverse the delirium, though the underlying dementia will persist.