Dementia is characterized by declines in memory and cognitive ability that interfere with activities of daily living. The most common types are Alzheimer disease (affecting 5 million Americans over age 65 years), vascular dementia, Lewy body dementia, and frontotemporal dementia. Diagnosing dementia requires exclusion of delirium and depression. Teasing out agerelated changes in cognition from mild cognitive impairment is also challenging. Less than 2% of patients with dementia have potentially reversible causes, such as hypothyroidism, medication side effects, normal pressure hydrocephalus, or major depression.

A meta-analysis identified potentially modifiable risk factors for developing Alzheimer disease, including physical inactivity, depression, smoking, midlife hypertension, midlife obesity, cognitive inactivity or low educational attainment, and diabetes. However, a 2011 NIH review concluded "currently, no evidence of even moderate scientific quality exists to support the association of any modifiable factors...with reduced risk for Alzheimer disease." The USPSTF did not find convincing evidence that pharmacologic or nonpharmacologic interventions could benefit patients with mild to moderate cognitive impairment. Consequently, the USPSTF issued an I statement (insufficient evidence) regarding screening for cognitive impairment.

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