The topic of dementia received little attention in the medical literature until about 70 years ago. The U.S. National Library of Medicine’s PubMed Web site listed only 3 references to dementia in 1935, a total of 25 in 1950, and approximately 550 in 1960. By 2007, there were over 90,000 references. Within the past 30 years, the general public has become familiar with dementia, in large measure due to the efforts of the Alzheimer’s Association.

People’s interest in the topic is evidenced by the fact that the Internet bookseller Amazon.com lists more than 25,000 titles that include the word dementia.

With regard to a specific disease, the prevalence of Alzheimer disease in the United States (estimated from a population-based, biracial urban study converted to prevalence estimates and applied to the U.S. population) was 4.5 million in 2000 by one widely accepted estimate (Hebert el al. 2003). This prevalence is expected to nearly triple, to 13.3 million, by 2050. If Alzheimer disease accounts for 56% of dementia cases, as indicated in the Framingham Study (Bachman et al. 1992), the total number of elderly persons in the United States with dementia in 2000 was more than 8 million. A 15-year epidemiological study that initially enrolled more than 1,600 nondemented persons age 65 years or older found that 5% of the deaths were attributed to Alzheimer disease, with an average time from onset to death of 5.9 years (Ganguli et al. 2005). Thus, Alzheimer disease and dementing illness in general are important public health issues, as discussed in Chapter 2 of this volume, “Epidemiology and Impact of Dementia.”

History of Dementia

The syndrome now known as dementia is a phenomenological diagnosis that is based on clinical observation. It has had various names over the past 2,500 years, including paranoia, idiotism, fatuity, acquired imbecility, senility, senile psychosis, and chronic organic brain syndrome. Hippocrates (circa 400 B.C.) identified the brain as the locus of mental function and was the first to recognize disorders of mental function as diseases, which he divided into epilepsy, mania, melancholia, and paranoia, the last term being equivalent to mental deterioration (Zilboorg 1941).

Although the early symptoms of the syndrome we now call dementia are cognitive and behavioral, astute observers differentiated this syndrome from other mental syndromes on the basis that its early effects were on memory and reasoning, recovery was infrequent, effects on the motor system were late, and it often progressed to total loss of self-care and communication. Causality was of course an issue. It had been observed since antiquity that cognitive functioning might become impaired following Head injury or in association with systemic disease, but that in some individuals no association (and therefore no presumed cause) could be found other than with the general deterioration of aging. It had also been observed that persons who lived to old age became increasingly impaired; eyesight and hearing faded, muscle mass and strength diminished, digestion and elimination slowed.

These observations gave rise to the concept of senility, the gradual wearing out of the organism. There is little doubt that individual organs and tissues do wear out over time; in fact, Drachman (2006a) recently presented an elegant argument for the role of entropy in late-onset Alzheimer disease. On the other hand, too ready an application of the wear-and-tear notion has concealed many of what we call diseases today. The attitude for which Robert Butler (1969) coined the term ageism had for many years discouraged inquiry into what appeared to be the “natural” process of physical and mental deterioration and the equation of old age to ill health.

The term dementia, which we now use to describe acquired global cognitive impairment (as opposed to amentia, or cognitive impairment evident from birth), is derived from the Latin de (out of ) + mens (mind) + ia (state of ); it literally means a state of being out of or deprived of one’s mind. It is one form of lunacy or insanity; the latter term was still in medical use through the 1920s as the overarching term for severe mental disorders.

The historical origin of the term dementia is unclear. Although attributed by Lipowski (1980) to Celsus in the first century A.D., the term does not appear in an English translation of Celsus’s (1756) De Medicina. The poet Juvenal, in the first or second century, is said to have used dementia in reference to the mental decrepitude of old age (Lipowski 1980), but the term was used through the nineteenth century (Thomas 1889) and is still used among the lay public today to designate mental derangements of many kinds. For example, someone might report, “The demented killer stalked his victims with great care and forethought before committing the horrible crime.” If the killer had been truly demented, this could hardly have been the case.