Brain networks underlying the clinical effects of long-term subthalamic stimulation for Parkinson's disease: a 4-year follow-up study with rCBF SPECT

The motor improvement derived from high-frequency deep brain stimulation (DBS) of the subthalamic nucleus (STN) in Parkinson's disease (PD) is maintained over time after surgery. The aim of the present prospective follow-up study was to assess regional cerebral blood flow (rCBF) changes related to such improvement in the long term. Methods: Ten PD patients with STN-DBS underwent 3 rCBF SPECT studies at rest-once preoperatively in the off-drug condition and the other 2 postoperatively in the off -drug/on-stimulation conditions at 5 +/- 2 and 42 +/- 7 mo. Patients were administered with Unified Parkinson Disease Rating Scale (UPDRS), Hoehn and Yahr (H&Y) scale, and Schwab and England (S&E) scale. Statistical parametric mapping was used to investigate rCBF changes during longterm STN stimulation in comparison with preoperative rCBF and the relationship between rCBF and UPDRS scores was used as a covariate of interest. Results: All patients showed a maximum clinical improvement during the first months after surgery and remained rather stable during further follow-up. The effect of STN-DBS from the pre- to the postoperative condition at 5 mo was to produce rCBF increases in the presupplementary motor area (pre-SMA), premotor (PMC), and dorsolateral prefrontal cortices. From the postoperative condition at 5 mo to that at 42 mo, the STN stimulation produced further rCBF increases in these frontal areas, and also in the primary motor/sensory cortices, globus pallidi, ventral lateral thalamic nuclei, cerebellum, pons, and midbrain entailing the substantia nigra (P < 0.0001). A correlation was detected between the improvement in motor scores and the rCEF increase in the pre-SMA and PMC (P < 0.0001). No correlation was present between the daily consumption of levodopa and the rCBF. Conclusion: Our study suggests that the long-term STN stimulation leads to improve- ment in neural activity in the frontal motor/associative areas. After an rCBF increase during the first months of stimulation, these regions showed a further increment in the later phase, which was accompanied by an increased activity in subcortical structures. The correlation between motor improvement and rCBF increase in higher order motor cortical areas suggests that even in the long term, as well as in the short term, the STN-DBS achieves its therapeutic benefit by restoring the activity within these cortical regions.