Four biomarkers for Alzheimer's disease could help identify how far the condition has progressed in particular patients, research suggests.
Dr Raymond Lo of the University of California, Berkeley, and his team showed amyloid deposition in the brain occurs early and before other degradation, such as atrophy.
A range of biomarker tests to detect the disease were shown to be sensitive at different stages of progression.
The findings suggest that repeated biomarker tests could predict the onset of the disease before symptoms first appear.
Early detection could help make treatment more effective, but studies have not yet explored whether tests developed to detect the disease are specific to different stages. At present, the only way to confirm the progression of Alzheimer's disease is at postmortem.
Dr Lo and colleagues examined 819 people aged 55-90 years with normal cognition, mild cognitive impairment or Alzheimer's disease.
Over three years, the researchers measured beta-amyloid 42 levels, fluorodeoxyglucose F18 (FDG) uptake, hippocampal volume and Alzheimer Disease's Assessment Scale-cognitive subscale score.
They found rates of change in beta-amyloid 42 did not differ across stages of the disease. But changes in glucose metabolism and hippocampal volume accelerated as cognitive function deteriorated.
The researchers said the finding implied that beta-amyloid 42 level in CSF declines before the onset of cognitive impairment.
However, measures of neuronal function and injury, such as glucose metabolism and hippocampal atrophy, change with disease stage.
The researchers concluded that the patterns of biomarkers 'capture Alzheimer's disease pathological states sequentially and that their predictive values for cognitive decline depend on the stage of the disease'.