Pharmacologic agents associated with a preventive effect on Alzheimer's disease: a review of the epidemiologic evidence.

Alzheimer’s disease is the most common subtype of dementia. This disease is diagnosed in approximately two thirds of all cases of dementia (1). According to current diagnostic criteria, a diagnosis of Alzheimer’s disease is considered probable when alternative causes of dementia have been excluded (2, 3). A clinical diagnosis of dementia is often made according to the Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised (DSM-III-R) criteria for dementia, with a subdiagnosis of Alzheimer’s disease made according to the National Institute of Neurological and Communicative Disorders and Stroke–Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA) criteria (2). The pathogenesis of Alzheimer’s disease is largely unknown. In short, the most frequently used explanation is that unknown genetic or environmental factors initiate a cascade of neuropathologic events that feature accumulation of β-amyloid and neurofibrillary tangles. This process is clinically characterized by a long latent phase, then a prodromal stage with a gradual and progressive decline in long-term episodic memory and impairment of other cognitive domains of mental functioning (4). Eventually, the person crosses a threshold of cognitive loss, after which the full syndrome is evident (5).