It suggests that erratic performance on cognitive tests may be a more useful marker of incipient dementia than the test scores themselves.
The study included 897 patients aged over 70 years who were not diagnosed with dementia at the time of testing. They completed neuropsychological tests measuring verbal IQ, attention and memory.
Over an average follow-up of 3.3 years, 61 incident cases of dementia were recorded. These included 47 cases of Alzheimer's and 18 cases of vascular dementia.
The researchers found that 43 per cent of those who developed dementia were in the highest quartile of variation across neuropsychological testing.
Increases in variability across neuropsychological tests were found to be predictive of a subsequent dementia diagnosis independently of performance on the tests.
The researchers concluded that variability in cognitive test performance could be used to predict onset of dementia independently of actual test scores.
JAMA 2008; 300: 823-30
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