Striatal dopamine transporter availability and individual clinical course within the 1-year follow-up of deep brain stimulation of the subthalamic nucleus in patients with Parkinson's disease

OBJECTIVE Degeneration of dopaminergic neurons in the substantia nigra projecting to the striatum is responsible for the motor symptoms in Parkinson's disease (PD). Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a well-established procedure to alleviate these symptoms in advanced PD. Yet the mechanism of action, especially the effects of STN-DBS on the availability of striatal dopamine transporter (DAT) as a marker of nigrostriatal nerve cell function, remains largely unknown. The aim of this study was therefore to evaluate whether 1) DAT availability changes within 1 year of STN-DBS and 2) the clinical outcome can be predicted based on preoperative DAT availability. METHODS Twenty-seven PD patients (mean age 62.7 +/- 8.9 years; mean duration of illness 13.0 +/- 4.9 years; PD subtypes: akinetic-rigid, n = 11; equivalence, n = 13; and tremor-dominant, n = 3) underwent [I-123]FP-CIT SPECT preoperatively and after 1 year of STN-DBS. DAT availability as determined by the specific binding ratio (SBR) was assessed by volume of interest (VOI) analysis of the caudate nucleus and the putamen ipsilateral and contralateral to the clinically more affected side. RESULTS Unified Parkinson's Disease Rating Scale (UPDRS) III scores improved significantly (mean preoperative on medication 25.6 +/- 12.3, preoperative off medication 42.3 +/- 15.2, postoperative on medication/off stimulation 41.4 +/- 13.2, and postoperative on medication/on stimulation 16.1 +/- 9.4; preoperative on medication vs postoperative on medication/on stimulation, p = 0.006), while the levodopa-equivalent daily dose was reduced (mean preoperative 957 +/- 440 mg vs postoperative 313 +/- 189 mg, p < 0.001). The SBR did not differ significantly before and 1 year after DBS, regardless of PD subtype. Preoperative DAT availability was not related to the change in UPDRS III score, but the change in DAT availability was significantly correlated with the change in UPDRS III score (contralateral head of the caudate VOI, p = 0.014; contralateral putamen VOI, p = 0.018). CONCLUSIONS Overall, DAT availability did not change significantly after 1 year of STN-DBS. However, on an individual basis, the improvement in UPDRS III score was associated with an increase in DAT availability, whereas DAT availability before STN-DBS surgery did not predict the clinical outcome. Whether a subtype-specific pattern of preoperative DAT availability can become a reliable predictor of successful STN-DBS must be evaluated in larger study cohorts.