Neuroimaging has provided key insights into the natural history of PD and has become a necessary if not sufficient test to assess potential new disease modifying therapies for PD. Although this review has focused on presynaptic dopamine ligands, several additional directions for imaging in PD have emerged or are under active study. Several postsynaptic dopamine imaging ligands have been used to study the postsynaptic dopaminergic receptors in PD (119-121), although quantitative information has been limited by relatively low sensitivity of the ligands available and has been complicated by uncertainty regarding endogenous dopamine binding to the receptor target. Postsynaptic dopamine receptor imaging studying dopamine release is a novel approach to using imaging to assess function, particularly in studies involving cell replacement therapy (122).
Although dopamine degeneration is a crucial feature of PD, it is clear that there is widespread degeneration in the brain in PD and that many clinical manifestations of PD are likely not due to dopamine deficiency. Ligands for nondopaminergic targets have been and are being developed to investigate nondopaminergic manifestations of PD and to better understand the cause of PD and of dyskinesia. The role of brain imaging in PD will continue to expand, as new imaging targets emerge and additional disease modifying drugs are developed. As simpler tools to identify preclinical "at risk" individuals become available, neuroreceptor imaging will be widely used to establish and monitor the onset and progression of disease. As treatments become available that target both the mechanisms that initiate and subsequently promote the course of disease progression, precise information about an individual's neurochemical status will be essential to optimize clinical management.
Was this article helpful?