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Research suggests the prevalence of dementia in developing countries is much higher than previously thought, indicating that policymakers should re-assess the burden on their health systems.

Previous studies have estimated dementia to be around a quarter to a fifth of developed country levels.

The 10/66 Dementia Research Group, a team of scientists composed mainly of developing country researchers, developed a tool for better diagnosing dementia in developing countries.

Their study, published in The Lancet online this week (28 July), compared this tool to the standard criteria used to determine dementia prevalence.

Almost 15,000 people over the age of 65 from China, Cuba, the Dominican Republic, India, Mexico, Peru and Venezuela were included in the study.

Participants and a relative were interviewed about the participant's cognitive function, physically examined and given a blood test. The data was then analysed using the standard criteria, DSM-IV, and the 10/66 criteria, which calculates the probability of dementia.

Diagnosis using the 10/66 criteria was consistently higher — usually around double that using DSM-IV. It was also more consistent across countries, varying from 5.6 per cent in rural China to 11.7 per cent in the Dominican Republic — DSM-IV results varied widely from country to country, from 0.3 per cent in rural India to 6.3 per cent in Cuba.

Many of the cases diagnosed by the 10/66 tool were not classed as dementia by the DSM-IV criteria, suggesting that 10/66 picked up more mild and moderate cases.

Martin Prince, professor of epidemiological psychiatry at King's College London and leader of the 10/66 group, says this is because the tool balances the cognitive tests used with the relative's interview to give a probability of whether the person has dementia, rather than relying on the 'tick-box' approach of DSM-IV.

Traditional respect for older people in developing countries may prevent relatives from talking about cognitive problems, Prince says.

They could also have symptoms of cognitive decline — such as failing to go shopping, cook, clean, or needing a huge amount of prompting with tasks and activities — that are simply not noticed due to the level of support they receive. These may be missed in DSM-IV diagnosis, says Prince.

The re-assessed rates of dementia are a warning to policymakers of the effects dementia could have on health systems, particularly as life expectancies increase.

"[Dementia is] important because it's very strongly linked with dependency. People need to consider disability and dependency as well as mortality when they're thinking about chronic diseases. All the focus is on cancer and cardiovascular disease and on deaths in people's 50s and 60s, whereas actually most of the pathology and burden will be from disability and dependence in older people," he says.


The Lancet (2008) doi:10.1016/S0140-6736(08)61002-8