Patients with mild cognitive impairment do not yet exhibit the criteria for the diagnosis of dementia, but may be in the early stages of Alzheimer's disease, which takes years to develop. But there has been no reliable diagnostic test to differentiate those that will go on to development dementia - and so might benefit from early intervention with cognitive or drug treatment - from those that are merely showing the first signs of old age.
"PET imaging with FDG represents one of the most promising tools for diagnosis of Alzheimer's," said Alexander Drzezga, who is the senior physician with the department of nuclear medicine at the Technical University of Munich in Germany.
Individuals with mild cognitive impairment are able to function reasonably well in everyday activities, such as managing finances and purchasing items at stores without assistance, but may have difficulty remembering details of conversations, events and upcoming appointments.
"A high percentage of mild cognitive impairment patients will develop Alzheimer's disease within a year; however, some of these patients will never develop dementia and may even improve with time," said Drzezga.
In the study, most patients who showed abnormalities typical of Alzheimer's in their original PET scan developed dementia within 16 months, while the majority of patients who did not show abnormalities in their original PET scan remained stable, he added.
The study also revealed that PET with FDG has a significantly higher accuracy for detection of Alzheimer's than genetic screening for the APOEe4-risk factor. In addition, using both PET with FDG and the APOEe4-genotype as genetic markers "allowed the definition of subgroups of patients with very high risk and with very low risk," said Drzezga. This finding could have implications for risk stratifying MCI patients in therapeutic trials.
Patients with Alzheimer's show characteristic changes of the cerebral glucose metabolic pattern, with a decrease in affected brain regions, he noted. PET imaging with FDG allows the analysis of regional cerebral glucose metabolism.
Although there is currently no cure for Alzheimer's, new treatments are on the horizon as a result of accelerating insight into the biology of the disease. "It is of increasing importance to identify 'converters' at the earliest possible stage of disease to develop and evaluate new and upcoming treatment options for Alzheimer's," added Drzezga.