According to British experts memory and language tests can diagnose 'hidden' early dementia.
While most dementias are missed for years as the symptoms are not clear until considerable brain tissue is lost, Oxford researchers were able to spot very early warning signs when they looked closely enough.
The results of the study could help doctors diagnose dementia sooner, which is crucial since treatment is most effective when given early.
For 20 years, the researchers studied a group of 241 healthy elderly volunteers, giving them regular tests designed to measure their thinking or cognitive powers. After analyzing the test results, the doctors found subtle clues that, in turn, hinted at ensuing impairment.
Specifically, the patients who went on to develop mild cognitive impairment or pre-dementia stumbled on tasks involving language expression, learning and recall.
For example, they had greater difficulty remembering the name for common objects or animals and explaining the meaning of a given word.
On the other hand, older people who scored lower on the language or memory tests tended to deteriorate more quickly.
Professor David Smith and his team have said that the findings fit with what we already know about dementia.
"This significant long-term study shows how subtle, but measurable, problems with language or memory can predict when a healthy elderly person is likely to develop mild cognitive impairment, which frequently develops into dementia," the BBC quoted Rebecca Wood of the Alzheimer's Research Trust as saying.
"Early intervention will be crucial for future dementia treatments. Being able to spot and measure the initial stages of dementia is a crucial challenge if we are to improve drug testing and lay the groundwork for prevention trials," she added.
The study has been published in Neurology.