A 68-year-old man with a 3-year history of progressive memory loss and difficulty with activities of daily living is brought to the psychiatry clinic by his family. He has insidious onset of cognitive decline, relatively preserved consciousness, and no recent infection or metabolic derangement. What is the most common cause of dementia in this clinical presentation?

Explanation

## Most Common Cause of Dementia **Key Point:** Alzheimer's disease (AD) accounts for 60–80% of all dementia cases, making it the most common neurodegenerative cause of cognitive decline in the elderly. ### Clinical Features Supporting Alzheimer's Disease | Feature | Alzheimer's Disease | Vascular Dementia | Lewy Body Dementia | | --- | --- | --- | --- | | **Onset** | Insidious | Stepwise | Insidious | | **Progression** | Gradual, progressive | Stepwise decline | Gradual | | **Memory** | Early and prominent | Variable | Later involvement | | **Consciousness** | Preserved early | Preserved | Preserved | | **Hallucinations** | Late, if any | Uncommon | Early, visual | | **Parkinsonism** | Absent | Absent | Present (RBD, rigidity) | | **Prevalence** | 60–80% of dementia | 15–20% | 5–10% | **High-Yield:** The patient in this vignette has: - Insidious onset (not stepwise) - Progressive course over years (not acute) - Preserved consciousness and alertness - No focal neurological signs mentioned - Age >65 (peak incidence for AD) These features are classic for Alzheimer's disease. ### Pathophysiology **Key Point:** Alzheimer's disease is characterized by accumulation of amyloid-β plaques and tau neurofibrillary tangles, leading to neuronal loss and progressive cognitive decline. **Clinical Pearl:** Memory loss in AD typically begins with difficulty recalling recent events (short-term memory), progressing to long-term memory loss and eventually global cognitive impairment. ### Why Alzheimer's is Most Common 1. **Age-related prevalence:** Incidence doubles every 5 years after age 65 2. **Pathological hallmark:** Amyloid-β and tau pathology is the most common neuropathological finding in elderly brains 3. **Epidemiological data:** In India and globally, AD accounts for >60% of dementia cases [cite:Harrison 21e Ch 435]