Dementia in developing nations may have been substantially underestimated

Different methods for calculating dementia prevalence have revealed that many cases may have been missed by conventional criteria. As such, the gap between dementia prevalence in less developed countries and higher-income countries may be much smaller than was thought. These are the conclusions of 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* in an Article published early Online and in an upcoming edition of The Lancet. The study, part funded by the The Wellcome Trust (UK) and the US Alzheimer's Association, will to be presented at the International Conference on Alzheimer's Disease (ICAD), Chicago, this weekend (the embargo above is timed to match the announcement of the findings).

A number of previous studies have suggested that prevalence of dementia in developing nations is much lower than in high-income countries, but the quality and evidence-base is poor, with very few published studies from Latin America, Africa, the Middle East, eastern Europe and Russia. In 1999, the 10/66 Dementia Research Group developed and validated its diagnostic methods in a large-scale pilot study across 25 low and middle income countries (LMIC). The 10/66 dementia diagnosis is based on a 2-3 hour assessment at the person's home, including a clinical interview, cognitive tests, and informant interviews. It is the balance of findings across these three elements that determines the 10/66 dementia diagnosis. The standard DSM-IV criteria are more restrictive, requiring memory impairment (which is not an early feature in some dementia subtypes), and clear evidence of social and occupational impairment (which is difficult to establish in LMIC settings). The 10/66 diagnosis may reveal more mild and moderate cases.

The 10/66 researchers found that prevalence of DSM-IV criteria varied widely, from 0.3% in rural India to 6.3% in Cuba. After standardisation for age and sex, DSM-IV prevalence in urban Latin America sites was 80% of that in Europe, but in China the prevalence was only half, and in India and rural Latin America a quarter or less of the European prevalence. However, 10/66 dementia prevalence was higher than that of DSM-IV dementia, and more consistent across sites, varying between 5.6% in rural China and 11.7% in the Dominican Republic. While 847 of the 1345 cases of 10/66 dementia were not confirmed as DSM-IV dementia cases, their validity was supported by high levels of associated disability.

The 10/66 authors, who will report more of their findings from their full network of 15 sites in 11 countries over the next few years, say: "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."

In an accompanying Comment, Dr Eric Larson, Group Health Center for Health Studies, Seattle, WA, USA and Dr Kenneth Langa, University of Michigan, Ann Arbor, MI, USA, say: "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."

Professor Martin Prince, Institute of Psychiatry at King's College London, UK T) +44 (0)7778 434 926 E) Martin.Prince@iop.kcl.ac.uk

For Dr Eric Larson, Group Health Center for Health Studies, Seattle, WA, USA please contact Joan DeClaire T) +1 206-947-4560 E) larson.e@ghc.org / declaire.j@ghc.org

Notes to editors: The 10/66 Dementia Research Group is so named to draw attention to the relative neglect of people with dementia living in developing countries by the global research community - just 10% of the research focussed upon the two thirds (66%) of those with dementia living in low and middle income countries (LAMIC). In the 10 years since its foundation in 1998, the group has

1. developed an innovative approach to culture and education-fair diagnosis
2. published some of the first accounts of care arrangements and caregiver strain, from pilot data in 26 LAMIC centres
3. worked with Alzheimer's Disease International and other international experts to estimate the numbers of people with dementia in all world regions and trends to 2040

for full study please e-mail tony.kirby@lancet.com