Nigrostriatal dysfunction in PET/SPECT
Nigrostriatal dopaminergic denervation can be shown using radiotracers that label presynaptic dopaminergic markers such as the striatal dopamine transporters (DAT) as routinely achieved with single-photon emission computed tomography (SPECT) or decarboxylase activity with 18F-Dopa positron emission tomography (PET). DAT imaging is closely correlated with post mortem SN cell counts [27] as well as severity and duration of disease [28] and has therefore been considered not only as a surrogate marker for disease progression, but also as a risk marker for PD [29]. Also, 18F-Dopa PET studies in PD patients have shown faster rates of tracer-uptake decline in earlier versus later disease stages and, in accordance with the pathological post-mortem studies, extrapolation of these exponential curves have led to estimates of prediagnostic PD of approximately 6 years[30–32].