512 Curr Neurol Neurosci Rep (2012) 12:511–519 Prevalence of Dementia in the Developing World Diagnosing Dementia There are many estimates of age-specific or age-and-gender- specific dementia prevalence in the developed world, based on epidemiological studies. However, WHO identified only 64 such studies in 14 developing countries [9 ]. Where such data are not available, estimates have been derived from a Delphi consensus of experts [10]. Furthermore, the age-specific and age-and-gender-specific estimates for de- veloping countries are often compared with estimates for developed countries, despite different population structures. Therefore, estimates of the prevalence of dementia in the developing world should be viewed with caution. Most estimates of the prevalence of dementia in people older than 60 years fall between 5 % and 7 % [3]. Variation in actual prevalence—as opposed to variation in detected dementia—is influenced by a number of factors. For exam- ple, low prevalence in sub-Saharan Africa (2.1 %) might be due to selective mortality of people younger than 60 years [11]. High prevalence in LAC (8.5 %) might be related to the high occurrence or confluence of genetic and/or envi- ronmental risk factors [5]. For example, increased mobility of individuals and families has spread genetic isolates with an extremely high prevalence of dementia, such as those with early-onset Alzheimer´s disease in Medellin, Colombia [12] and Huntington’s disease in Maracaibo, Venezuela [13]. The fact that expression of the disease occurs after reproductive age might also contribute to its spread. Finally, in consanguineous marriages, which are relatively common in some resource-poor areas, dementia in either or both parents increases the risk of having children who will be affected in the future [14]. Population demography and other factors play an impor- tant role in determining the prevalence of dementia. Both prevalence and incidence of dementia increase exponential- ly with age, making age the main risk factor for the disease [9 , 15]. The number of people at risk of dementia in the developing world will increase rapidly during the next 50 years, because the population and proportion will grow faster for the elderly (≥60 years) than for other age groups [16]. In India, for example, the population of individuals ≥80 years will increase from 5.4 million in 2001 to 32 million in 2051 [17]. In addition to aging populations, gradual improvements in health care in developing countries are probably increasing the time that affected individuals survive with dementia [18]. Other factors that might affect the incidence of certain types of dementia—for example, cardiovascular risk factors, such as obesity, metabolic syndrome, and sed- entary life—are also escalating much more rapidly in developing than in developed countries [19–22]. In con- sequence, the dementia burden in the developing world is expected to increase significantly. Diagnosis of dementia and accurate determination of sub- type early in the course of the disease are crucial for optimal clinical care and management. Traditionally, dementia has been defined as a global impairment of intellectual function that requires anatomopathological examination to provide accurate diagnosis and differentiation among subtypes [23–25]. However, research involving biomarkers and neu- rogenetics now allows identification of patients years, per- haps decades, before the diagnosis of dementia is made, such as in presymptomatic Alzheimer´s disease [26]. The National Institute on Aging and the Alzheimer´s Association recently released revised criteria for all-cause dementia [27], which include neuropsychiatric or cognitive symptoms, rather than just cognitive deficits, that interfere with daily functioning, represent a decline from previous levels, and are not explained by delirium or major psychi- atric disorders. A new category was added, primarily intended for research purposes: dementia due to possible or probable Alzheimer´s disease with evidence of the Alzheimer pathology. The new category requires that a subject meeting the clinical criteria for Alzheimer´s disease also exhibits changes in biomarkers related to the current understanding of the pathophysiology [28]. The revised crite- ria for Alzheimer´s disease include a predementia stage, in which a subject is asymptomatic but shows evidence of the underlying brain pathology specific for Alzheimer´s disease. These new criteria will be of limited use in the developing world, because the ability to detect relevant biomarkers and pathologies is low, due to the high cost of testing and the lack of infrastructure. To establish a diagnosis of dementia, an evaluation fo- cuses on, as a clinical syndrome, cognitive performance and behavior of the subject, changes in the activities of daily living, and exclusion of other possible causes. Diagnosing dementia, particularly in the early stages, is neither simple nor straightforward. The clinical interview is considered to be an art. The first step is usually to elicit a complete history of signs and symptoms, recalled and recounted by the pa- tient and/or an informant. A highly skilled interviewer struc- tures the interaction as a conversation, establishing rapport and confidence and enabling the patient to fully disclose even embarrassing details. Neuropsychological, neuroimag- ing, and other diagnostic tests are used to distinguish path- ological changes within the brain that characterize different dementia syndromes. Interpretation of the clinical interview and test results requires training and often varies among individuals making the judgment. The clinician uses as many tools as possible—clinical examination, laboratory tests, neuroimaging, genetic testing—to determine the underlying pathology or type of dementia and establish the best therapeutic course as