Reductions in the thickness of the brain's cortex could be used to identify those at risk and when the disease might develop, researchers said.
Scientists from Massachusetts General Hospital in Charlestown, Massachusetts, used MRI scans to study 65 cognitively normal adults over an 11-year period.
They found that around half of the participants who had reduced cortical thickness went on to develop Alzheimer's, compared with none of those who did not show reductions.
These reductions also predicted the time to diagnosis of Alzheimer's. One standard deviation reduction in thickness was associated with a three-fold increase in risk of developing the disease.
Writing online in the journal Neurology, the researchers said: 'The present data demonstrate that in cognitively normal older adults a thinner cerebral cortex in regions typically affected by Alzheimer's disease is predictive of time to onset of Alzheimer's disease dementia.'
The researchers said changes in cortical thickness could be used as a measure of early neurodegenerative change in preclinical Alzheimer's disease.
They said the finding provided 'an additional tool to link the biological changes of the disease with the symptoms of the illness'.