Striatal dopaminergic system in dopa-responsive dystonia: a multi-tracer PET study shows increased D2 receptors.

We investigated the integrity of striatal dopaminergic system in seven patients with dopa-responsive dystonia (DRD). Dopamine transporter function ([(11)C]CFT) and D1 ([(11)C]NNC 756) and D2 receptors ([(11)C]raclopride) were studied in same patients using positron emission tomography. Compared to age-adjusted control values the dopamine D2 receptor availability was increased in DRD. The mean age-adjusted [(11)C]raclopride uptake was 116% of the control mean in the putamen (p = 0.004) and 114% in the caudate nucleus (p = 0.007). The mean [(11)C]NNC 756 uptake was not different between DRD patients and controls, the age-adjusted uptake in DRD being 93% of mean control value in the putamen (p = 0.20) and 95% in the caudate nucleus (p = 0.40). The dopamine transporter binding was not altered. The [(11)C]CFT uptake in DRD was 96% of the control value in the putamen (p = 0.64), and 95% in the caudate nucleus (p = 0.44). In conclusion, striatal dopamine D2 receptors availability is increased in DRD whereas dopamine D1 receptors and dopamine transporter ligand binding is unchanged. The pattern of changes in striatal dopaminergic system in DRD is different from that reported in juvenile Parkinson's disease. The increased D2 receptor availability may be due to reduced competition by endogenous dopamine or a compensatory response to dopamine deficiency, or both.