Neuroimaging in the early diagnosis of neurodegenerative disease

Neurodegenerative disorders, of which Alzheimer's (AD) and Parkinson's (PD) diseases are the most common, take an enormous toll on affected patients and their families. For example, a recent analysis indicates that dementia and PD combined affect more than 7.5 million Europeans, at an estimated annual cost of €120 billion [1] and incalculable suffering. While symptomatic therapies are currently available, they are at best imperfect (PD), at worst provide only modest benefit (dementia) and they do not have any convincing impact on the inexorable progression of the underlying disorder. Advances in basic neuroscience make it increasingly likely that disease modifying therapies will be developed but these are likely to have maximal impact if they are introduced early in the course of the illness. Early disease detection would permit the provision of such therapies to those most likely to benefit from them, at the time that they are most likely to be effective. Early diagnosis permits the identification of people appropriate for inclusion in clinical trials of novel therapies and the exclusion of those who are not. Finally, early diagnosis allows better prognostication and appropriate resource utilization.A variety of neuroimaging techniques may be useful for the early diagnosis of neurodegenerative disorders, but one should first consider the goal. Early diagnosis may refer to the timely correct differentiation of a specific disease entity from other conditions that may mimic it in early stages, or it may refer to the early detection of central nervous system dysfunction, prior to the emergence of clinical symptoms. The latter application is more likely to be of interest in populations at increased risk of disease, and could be useful for identification of subjects to participate in trials of neuroprotective agents, or ultimately to try and halt disease progression once effective disease-modifying interventions have been identified.In the case of PD, the two major diagn