Optimizing diagnosis in Parkinson's disease: Radionuclide imaging.

Parkinson's disease (PD) and other disorders characterized by basal ganglia dysfunction are often associated with limited structural imaging changes that might assist in the clinical or research setting. Radionuclide imaging has been used to assess characteristic functional changes. Presynaptic dopaminergic dysfunction in PD can be revealed through the imaging of different steps in the process of dopamine synthesis and storage: L-aromatic amino acid decarboxylase (AADC) activity, Vesicular Monoamine Transporter type 2 (VMAT2) binding or its reuptake via the dopamine transporter (DAT). Postsynaptic dopamine dysfunction can also be studied with a variety of different tracers that primarily assess D2-like dopamine receptor availability. The function of other neurotransmitters such as norepinephrine, serotonin and acetylcholine can be imaged as well, giving important information about the underlying pathophysiologic process of PD and its complications. The imaging of metabolic activity and pathologic changes has also provided great advances in the field. Together, these techniques have allowed for a better understanding of PD, may be of aid for differentiating PD from other forms of parkinsonism and will undoubtedly be useful for the establishment of new therapeutic targets.