Diagnostic value of asymmetric striatal D2 receptor upregulation in Parkinson's disease:: an [123I]IBZM and [123I]FP-CIT SPECT study

Introduction Striatal postsynaptic D-2 receptors in Parkinson's disease (PD) are thought to be upregulated in the first years of the disease, especially contralateral to the clinically most affected side. The aim of this study was to evaluate whether the highest striatal D-2 binding is found contralateral to the most affected side in PD, and whether this upregulation can be used as a diagnostic tool. Methods Cross-sectional survey was undertaken of 81 patients with clinically asymmetric PD, without antiparkinsonian drugs and with a disease duration of <= 5 years and 26 age-matched controls. Striatal D-2 binding was assessed with [I-123]IBZM SPECT, and severity of the presynaptic dopaminergic lesion with [I-123]FP-CIT SPECT. Results The mean striato-occipital ratio of [I-123]IBZM binding was significantly higher in PD patients (1.56 +/- 0.09) than in controls (1.53 +/- 0.06). In PD patients, higher values were found contralateral to the clinically most affected side (1.57 +/- 0.09 vs 1.55 +/- 0.10 ipsilaterally), suggesting D-2 receptor upregulation, and the reverse was seen using [I-123]FP-CIT SPECT. However, on an individual basis only 56% of PD patients showed this upregulation. Conclusion Our study confirms asymmetric D-2 receptor upregulation in PD. However, the sensitivity of contralateral higher striatal [I-123]IBZM binding is only 56%. Therefore, the presence of contralateral higher striatal IBZM binding has insufficient diagnostic accuracy for PD, and PD cannot be excluded in patients with parkinsonism and no contralateral upregulation of D-2 receptors, assessed with [I-123]IBZM SPECT.