Early-stage [¹²³I]β-CIT SPECT and long-term clinical follow-up in patients with an initial diagnosis of Parkinson's disease

Purpose: Previous studies using dopamine transporter single-photon emission computed tomography (SPECT) to try and distinguish between patients with idiopathic Parkinson's disease (IPD) and patients with atypical parkinsonian syndromes (APS) have mainly focussed on patients with an already established clinical diagnosis of several years' duration. Differences in the pattern of striatal involvement between IPD and APS have been found in only few studies. We hypothesized that distinguishing SPECT features might be most pronounced at an early disease stage, and the purpose of the present study was to investigate this hypothesis. Methods: The study included 72 patients with an initial clinical diagnosis of IPD, supported by decreased striatal [¹²³I] β-CIT binding on baseline SPECT. In ten patients, the diagnosis was changed to APS over a mean follow-up period of 62 months. We retrospectively compared the patterns of striatal involvement on the baseline SPECT scans between the group of patients (re)diagnosed with APS and the remaining 62 patients in whom a diagnosis of IPD was maintained. Results: In the group of patients with APS, baseline [¹²³I]β-CIT binding in both caudate nuclei was lower than in the group of patients with IPD. In addition, putamen to caudate binding ratios were higher in the group of APS patients. In spite of these differences, individual binding values showed considerable overlap between the groups. Conclusion: [¹²³I]β-CIT SPECT scanning in early-stage, untreated parkinsonian patients revealed a relative sparing of the caudate nucleus in patients with IPD as compared to patients later (re)diagnosed with APS. Nevertheless, the pattern of striatal involvement appears to have little predictive value for a later re-diagnosis of APS in individual cases.