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DSM-IV criteria may underestimate dementia rates in lower-income countries

Dementia rates in low- and middle-income countries were approximately twice as high as the rates reported using DSM-IV criteria, according to the 10/66 Dementia Research Group. The London-based research organization’s study results may support evidence for the cognitive reserve hypothesis, namely that education, literacy, verbal fluency and motor sequencing can provide substantial protection against the onset of dementia.

“Results of the 10/66 Dementia Research Group population-based studies in Latin America, India and China suggested that dementia prevalence might be underestimated when the widely used [DSM-IV] diagnostic criteria are applied, particularly in rural and less developed sites,” the researchers wrote.

The study researchers, led by Martin Prince, MD, MSc, FRCPsych, professor of epidemiological psychiatry at the Institute of Psychiatry in London and co-director of the Centre for Global Mental Health, performed a population-based cohort study of all people aged 65 years and older living in urban sites in Cuba, the Dominican Republic and Venezuela, and rural and urban sites in Peru, Mexico and China. The researchers assessed incidence rates according to criteria both from the 10/66 Dementia Research Group and the DSM-IV.

The 10/66 Dementia Research Group, part of Alzheimer’s Disease International, is a collective of researchers carrying out population-based research into dementia, non-communicable diseases and aging in low- and middle-income countries. According to the research group, 10/66 criteria for assessing dementia prevalence involve “a comprehensive cross-cultural comparison [that] requires estimation of incidence rates and absolute and relative mortality risks for people with dementia.”

The researchers used questionnaires to obtain information about age, sex, education level, literacy, occupational attainment, number of household assets and mortality information from all sites. The baseline survey consisted of a clinical interview, an informant interview and a physical examination.

Of the 12,887 participants interviewed at baseline, 11,718 were free of dementia, and 8,137 were interviewed again. The 10/66 dementia rates varied between 18.2 and 30.4 per 1,000 person-years and were 1.4 to 2.7 times higher than the rates reported using DSM-IV criteria. Mortality hazards were 1.56 to 5.69 times higher in those with dementia vs. those without dementia. The overall incidence of dementia before death might be 4% to 19% higher if data from informant reports were included, according to the researchers. Incidence of dementia using 10/66 criteria was independently associated with increased age (HR=1.67; 95% CI, 1.56-1.79), female sex (HR=0.72; 95% CI, 0.61-0.84) and low education (HR=0.89; 95% CI, 0.81-0.97), but not with occupational attainment (HR=1.04; 95% CI, 0.95-1.13).

Results also showed that incidence of dementia was lowest in Peru (18.2; 95% CI, 14.3-23.0) and highest in Mexico (30.4; 95% CI, 25.5-36.3).

According to the researchers, those who met 10/66 criteria for dementia but did not meet DSM-IV criteria at baseline had a very high incidence of DSM-IV dementia during the follow-up period, further supporting the validity of the research group’s assessment methods, they said.

“The DSM-IV dementia criterion identifies a severe form of dementia with high diagnostic reliability, but findings from our previous work suggests systematic underestimation, particularly in low-income and middle-income countries where awareness of dementia is lower than in high-income countries, and where older people are routinely supported in many core and instrumental activities of daily living,” the researchers wrote.

Disclosure: The researchers report no relevant financial disclosures. Alzheimer’s Disease International is supported in part by grants from GlaxoSmithKline, Novartis, Lundbeck, Pfizer and Eisai.