The gap between prevalence of dementia in developing and higher-income countries may be much smaller than previously estimated, according to a study released on July 28, 2008 in The Lancet.

Previously, studies have indicated that dementia is less prevalent in developing countries than in high income countries, a difference that has been attributed to a relatively aged population in the latter. However, according to the background information in the article, these previous studies lack quality and need a wider evidence base, particularly in studies from Latin America, Africa, the Middle East, eastern Europe and Russia.

In 1998, the 10/66 Dementia Research Group was established as a part of the Alzheimer’s Disease International, based in King’s College London, in order to draw attention to the disparity in research of dementia in developing and high-income countries. At the time, while 66% of patients with dementia were living in low and middle income countries (LMIC), only 10% of research focused on this population.

In 1999, the group developed and validated diagnostic methods of this disease in a large-scape pilot study in 25 LMICs. Their diagnosis is based on a 2-3 hour assessment in the home of the subject, including a clinical interview, cognitive tests, and informant interviews. Balancing these results then leads to a diagnosis. These are generally less restrictive than the standard Diagnostic and Statistical Manual of Mental Disorders (DSM-I) criteria, which include: memory impairment, which is not an early feature of certain dementia subtypes; and clear evidence of social and occupational impairment, which can be difficult to establish in LMIC settings. As a result, the 10/66 diagnostic criteria may reveal more subtle cases.

To learn more about dementia in developing populations, Professor Juan Llibre Rodriguez, Medical University of Havana, Cuba, and Professor Martin Prince, Institute of Psychiatry at King’s College London, UK, and colleagues from the 10/66 Dementia Research Group evaluated 14,960 subjects in China, India, Cuba, Dominican Republic, Venezuela, Mexico, and Peru aged 65 years and older. Both the 10/66 and DMV-I criteria were used and the latter was compared to previously published studies in European countries.

According to the DSM-IV criteria, the prevalence of dementia varied widely, as low as 0.3% in rural India and as high as 6.3% in Cuba. When adjusted for age and sex, in comparison to European estimates, the DSM-IV prevalence was 80% of this in urban Latin American sites, 50% of this in China, and less than 25% of this in India and rural Latin America. The prevalence of dementia according to the 10/66 guidelines was generally higher and more consistent across the populations, with prevalence as low as 5.6% in rural China and as high as 11.7% in the Dominican Republic. OF the 1,345 cases of 10/66 dementia, 847 were not confirmed by DSM-IV criteria, the authors supported this with evidence of high levels of associated disability.

The authors close with warning about the underestimates of dementia in LMIC countries: “Our conclusion is that the DSM-IV dementia criterion might substantially underestimate the true prevalence of dementia, especially in least developed regions, because of difficulties in defining and ascertaining decline in intellectual function and its consequences. We believe that our methods have drawn attention to a substantial prevalence of dementia that might have been missed. Prevalence differences between developed and developing countries might not be as large as previously thought.”

Dr Eric Larson, Group Health Center for Health Studies, Seattle, WA, USA and Dr Kenneth Langa, University of Michigan, Ann Arbor, MI, USA, contributed an accompanying comment in which they support the 10/66 criteria in this analysis. “The 10/66 study will provide unique opportunities to explore environmental effects on the ageing process in the brain…we applaud the 10/66 authors’ focus on actual function and especially functional impairment, which leads to suffering and dependency. We should work towards letting more of the world’s people experience long life as a reward for their many years of life on earth – not as punishment for the triumphs of modern medicine and public health.” They say.

This study will be presented at the International Conference on Alzheimer’s Disease (ICAD) the weekend of July 26. These results will be expanded over the next few years, as the 10/66 group collects more data from their network of 15 sites in 11 different countries.

Prevalence of dementia in Latin America, India, and China: a population-based cross-sectional survey
Juan J Llibre Rodriguez, Cleusa P Ferri, Daisy Acosta, Mariella Guerra, Yueqin Huang, K S Jacob, E S Krishnamoorthy, Aquiles Salas, Ana Luisa Sosa, Isaac Acosta, Michael E Dewey, Ciro Gaona, A T Jotheeswaran, Shuran Li, Diana Rodriguez, Guillermina Rodriguez, P Senthil Kumar, Adolfo Valhuerdi, Martin Prince, for the 10/66 Dementia Research Group
Published Online The Lancet July 28, 2008
DOI:10.1016/S0140-6736(08)61002-8
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The rising tide of dementia worldwide
Published Online The Lancet July 28, 2008
DOI:10.1016/S0140-6736(08)61003-X
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Written by Anna Sophia McKenney