Deep brain stimulation of the subthalamic nucleus in advanced Parkinson's disease: five year follow-up at a Portuguese center

Introduction. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) in Parkinson's disease (PD) is safe and effective. Most series report stable long-term motor responses. Aim. To report the long-term outcome of STN-DBS in advanced stage PD patients at a Portuguese center. Patients and methods. Motor status was evaluated before surgery ('off' medication and best 'on'), post-operatively, and at five years ('on' medication and stimulation) using UPDRS part III. Axial symptoms subscores were quantified. Disability was assessed with the modified Rankin Scale (mRS). Development of dementia was assessed at 6 months and five years post-DBS. Results. Of the 183 patients submitted to STN-DBS, 71 had completed 5 years of follow-up. Ten patients were not included: two died (cancer, myocardial infarction), five were lost to follow-up and three had their stimulation systems removed. Motor function improved by 78% and 66% postoperatively and at five years, respectively. There was improvement of axial symptoms postoperatively, with significant worsening at five years (p < 0.001). mRS scores improved postoperatively, but declined at five years, although most patients (88.5%) remained ambulatory (mRS < 4). One patient (1.6%) and 19 patients (31,2%) were demented at 6 months and 5 years, respectively. Patients who developed dementia were significantly older than non-demented patients (56.5 +/- 7.8 vs 63.7 +/- 5.9 years-old; p < 0.001). Conclusions. In this series STN-DBS proved its efficacy regarding motor symptom improvement even five years after the procedure. Deterioration of axial symptoms and disability, as well as new onset dementia were observed in this period, but the possible role of STN-DBS as a causative factor is yet to be defined.