A 68-year-old man with a 5-year history of progressive memory loss and word-finding difficulty is brought to the clinic. His family reports that his cognitive decline has been steady and predictable. On examination, he is alert and attentive. Which single feature MOST strongly suggests dementia rather than delirium?

## Temporal Course as the Gold Standard Discriminator **Key Point:** The INSIDIOUS onset with STEADY PROGRESSIVE course over YEARS is the single most reliable feature distinguishing dementia from delirium. ### Why Temporal Pattern Is Diagnostic The history provided—5 years of gradual, predictable cognitive decline—is pathognomonic for dementia. This extended timeline and steady progression rule out delirium, which develops acutely (hours to days) and fluctuates. ### Clinical Reasoning ```mermaid flowchart TD A[Cognitive Decline Reported]:::outcome --> B{Timeline of Onset?}:::decision B -->|Acute: hours-days| C[Fluctuating course?]:::decision B -->|Insidious: months-years| D[Steady progression?]:::decision C -->|Yes| E[DELIRIUM]:::urgent C -->|No| F[Other acute disorder]:::outcome D -->|Yes| G[DEMENTIA]:::outcome D -->|No| H[Atypical presentation]:::outcome ``` **High-Yield:** A 5-year history automatically excludes delirium. Delirium resolves (if reversible) or progresses to death within weeks to months. Dementia persists for years to decades. **Clinical Pearl:** Preserved consciousness and attention early in dementia can coexist with profound memory loss. In delirium, attention is ALWAYS impaired. However, the temporal course is more discriminating than any single cognitive domain. ### Why Each Feature Matters | Feature | Delirium | Dementia | |---------|----------|----------| | **Onset timeline** | Hours–days | Months–years | | **Course pattern** | Fluctuating | Steady, progressive | | **Consciousness** | Always altered | Normal early | | **Attention** | Always impaired | Preserved early | | **Reversibility** | Often reversible | Usually irreversible | **Mnemonic: DEMENTIA = DURATION** — **D**uration is years, not days; **E**very day similar (not fluctuating); **M**emory loss prominent; **E**arly consciousness preserved; **N**eurodegeneration (structural); **T**ime-tested diagnosis; **I**nsidious onset; **A**ttention relatively spared early.