- Alzheimer disease (AD) is a progressive, irreversible, degenerative neurologic disease that results in neuron death.
- AD represents 60–80% of dementia.
- AD is the sixth leading cause of death in the United States.
- People aged ≥65 years with new AD live 4 to 8 years on average.
- AD is underdiagnosed (~50%), and >50% with AD unaware of diagnosis
- Economic burden in 2018: ~$305 billion, projected $1.1 trillion by 2050
- Dementia should be distinguished from:
- Age-related cognitive decline: lifelong changes in mental ability and memory; part of normal aging
- Mild cognitive impairment (MCI): greater impairment than cognitive decline
- MCI: People are generally able to live independently from a cognitive perspective.
- MCI: affects 15–20% of those aged ≥65 years, with 32–38% developing dementia ≤5 years
- AD diagnostic classification:
- Preclinical AD: no cognitive symptoms, AD biomarkers present
- MCI due to AD: very mild impairment
- Dementia due to AD:
- Mild: impairment in some activities
- Moderate: impairment in many activities
- Severe: impairment in most activities
- System(s) affected: nervous
- Synonym(s): presenile dementia; senile dementia of the Alzheimer type
- Predominant age: >65 years
- Incidence: females = males
- Prevalence: females > males
New cases of AD in the United States: 484,000/year
- 65 to 75 years: 2 new cases per 1,000 people
- 75 to 84 years: 11 new cases per 1,000 people
- ≥85 years: 37 new cases per 1,000 people
<5.8 million in the United States; <44 million worldwide
- 13.8 million in the United States by 2050
- 1 in 10 of those aged ≥65 years have AD dementia.
- 32% of those aged ≥85 years have AD dementia.
- ~200,000 in United States with early-onset AD (age <65 years)
Etiology and Pathophysiology
- Progressive, irreversible disease, worsening cognitive impairment
- β-Amyloid plaques outside of neurons and τ protein tangles inside of neurons, resulting in loss of connections and neuron death.
- Age, genetics, systemic diseases, and lifestyle behaviors may influence AD progression.
- Autosomal dominant: <5% of AD, usually early onset (age <65 years)
- Familial inheritance AD (nonautosomal dominant): 15–25% of AD
- Nonmodifiable risk factors: (1),(2)
- Age, gender (due to longer lifespan in women)
- Family history, genetic mutations
- APOE-e4 gene variant: e4 heterozygous 2- to 3-fold risk; e4 homozygous 8-fold risk
- Racial and ethnic differences in AD exist.
- Cardiovascular disease–related risk factors:
- Hypertension (HTN) (especially in midlife years); hyperlipidemia
- Obesity, diabetes, and impaired glucose processing
- Tobacco use, unhealthy diet, lack of physical activity
- Cerebrovascular (stroke) risks and injury
- Other potentially modifiable risk factors:
- Fewer years of formal education (<8th grade)
- Lack of continuous brain activity—learning
- Traumatic brain injuries: repetitive mild and moderate/severe
- Lack of social engagement
- Late-life depression
- Poor quality and inadequate sleep
- Hearing and vision deficits
- High alcohol consumption
- Possible environmental factors (e.g., pollution)
- Cognitive decline and impairment are top concerns of people aged ≥50 years.
- Treat psychiatric conditions and avert delirium during hospitalizations.
Commonly Associated Conditions
- Down syndrome
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