= acquired progressive global impairment of intellectual functioning

Prevalence: 35 million worldwide; rising due to increase in life expectancy; in USA 14% of population >65 years of age and >50% of individuals >85 years

Dx: multiple cognitive deficits representing a decrease from baseline + interfering with social / professional function including impairment of (1) memory (2) motor activity (3) recognition (4) executive function

Etiology: may be caused by more than 80 diseases

1. CORTICAL
   1. Alzheimer disease
   2. Pick disease = frontotemporal dementia
   3. Mild cognitive impairment
   4. Creutzfeldt-Jakob disease
2. SUBCORTICAL
   1. Vascular dementia: multi-infarct, Binswanger, CADASIL = cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy)
   2. Dementia with Lewy bodies
   3. Huntington disease
   4. Parkinson disease
   5. Wernicke-Korsakoff syndrome
   6. Wilson disease
   7. Multiple sclerosis
   8. Infectious etiology (HIV, Lyme disease, syphilis)
   9. Dementia syndrome of depression
3. OTHERS
   1. MELAS
   2. Cortical venous thrombosis
   3. Normal pressure hydrocephalus
   4. Subdural hematoma
   5. Brain mass (CNS lymphoma + other neoplasms)

In order of frequency:

1. Alzheimer disease 60–70%
2. Dementia with Lewy bodies 25%
3. Frontotemporal dementia 5–10%
4. Vascular dementia ?% (declining)
5. Mixed etiology 6%
6. Normal pressure hydrocephalus 1%
7. Depression 1%
8. Tumor 1%