Background: Alzheimer’s disease (AD) is the most common of the dementia disorders, and age is the main risk factor. In Norway, there are approximately around 60 000 demented persons, and the prevalence is expected to increase more than twofold over the next 40 years. AD is a neurodegenerative disease, and the pathology probably starts many years before the onset of symptoms. Early diagnosis has to an increasingly extent come into focus of AD research. There is the comprehension that drug intervention, when available, should start at an early phase of the disease, before extensive irreversible neuronal damage occurs. Biomarkers of the disease can be measured in vivo, and are associated with specific features of the pathophysiological processes. Cerebral glucose metabolism and amyloid depositions measured by positron emission tomography (PET) are such biomarkers, and the aim of this review is to evaluate these in early Alzheimer’s disease. Results from the most important longitudinal PET studies of subjects with mild cognitive impairment are collected and compared, and the ability of baseline PET measurements to predict future conversion to AD or cognitive decline is of special interest.
Methods: Literature study based on non-systematic search in the PubMed database.
Main results: 18F-fluoredeoxyglucose PET measurements are able to predict future AD with accuracies ranging from 56 – 90 %, sensitivities from 57 – 93% and specificities from 47 – 91%. Retention of the amyloid binding 11C-Pittsburgh compound B (PiB) predicts AD with accuracies ranging from 65 – 87 %, sensitivities from 93 – 100 % and specificities from 56 – 81 %. Patterns of glucose hypometabolism and amyloid depositions are rather consistent in the different studies.
Concluding remarks: Some of the longitudinal studies achieved good accuracies and show that AD can be diagnosed in an early phase using PET.