Clinical and Imaging Progression in the PARS Cohort: Long‐Term Follow‐up

Background and Objectives The PARS (Parkinson Associated Risk Syndrome) study was designed to test whether screening for hyposmia followed by dopamine transporter imaging can identify risk for conversion to clinical PD, and to evaluate progression markers during the prodromal period. Methods Subjects with hyposmia completed annual clinical evaluations and biennial [123I]ß‐CIT single‐photon emission computed tomography scans. Subjects were categorized as normal (>80% age‐expected tracer uptake; n = 134), indeterminate (>65–80%; n = 30), and dopamine transporter deficit (≤65%; n = 21) by their baseline scan, and survival analysis was used to compare risk of conversion to motor PD. Progressing to a scan with a dopamine transporter deficit was assessed for those subjects with either normal or indeterminate baseline imaging. Results Over a mean of 6.3 [standard deviation: 2.2] years of follow‐up, 67% (n = 14) of dopamine transporter deficit subjects, 20% (n = 6) of dopamine transporter indeterminate subjects, and 4% (n = 6) of dopamine transporter normal subjects converted to a PD diagnosis (P