Striatal D 2 receptor status in patients with Parkinson's disease, striatonigral degeneration, and progressive supranuclear palsy, measured with 11 C‐raclopride and positron emission tomography

Equilibrium striatal: cerebellar 11 C‐raclopride (RAC) uptake ratios reflect the density of striatal dopamine D 2 binding sites. Using positron emission tomographic scanning we have measured striatal RAC uptake in 6 untreated patients with Parkinson's disease (PD), 5 chronically treated patients with PD and a fluctuating response to L ‐dopa, 10 patients with striatonigral degeneration (SND), and 9 patients with progressive supranuclear palsy (PSP). Regional cerebral blood flow was determined also, with C 15 O 2 . Mean strital: cerebellar RAC uptake was not significantly different from normal in untreated patients with PD, though 2 of these 6 patients showed significantly increased putamen tracer binding. Mean caudate and putamen: cerebellar RAC uptake ratios of the group with PD and fluctuating response to L ‐dopa were significantly reduced by 30% and 18%, respectively. The patients with SND had lesser, but significant, 10% and 11% decreases in mean caudate and putamen: cerebellar RAC uptake ratios, respectively, whereas patients with PSP showed 24% and 9% reductions in caudate and putamen: cerebellar RAC binding. Striatal and frontal blood flow were significantly reduced in patients with PSP, but not in patients with PD or SND. In conclusion, striatal D 2 binding potential is normal or raised in untreated patients with PD, but reduced in patients with PD and a fluctuating response to L ‐dopa. Patients with SND and PSP show a decrease in striatal RAC binding, but to a lesser extent than patients with PD and a fluctuating response to treatment. Failure of patients with SND and PSP to respond well to L ‐dopa cannot therefore be due to losss of striatal D 2 sites alone, but must reflect loss of other basal ganglia connections.