Bilateral Pallidal Stimulation in Patients With Advanced Parkinson's Disease-LATESTIM

Inclusion Criteria: * Parkinson's disease according to the UKBB criteria, with the exception that familial forms of otherwise typical parkinsonian syndromes may also be included * motor complications of dopaminergic medication (dyskinesia or motor fluctuations or both) that are at least moderately bothersome to the patient \[on a scale of 5 possible levels: not at all / mildly / moderately / severely / extremely bothersome\] * Presence of at least one of the following absolute exclusion criteria for STN stimulation: * Mattis dementia rating scale \<130 points * postural instability of \>1 in the item of MDS-UPDRS III \[item #12\] "on" medication * less than 30% improvement of axial score in the acute levodopa challenge test \[axial score =sum of items 3.1, 3.9, 3.10, 3.12, 3.13 of the MDS UPDRS III\] * or presence of at least two of the following relative exclusion criteria for STN stimulation: * age \> 70 years * Mattis dementia rating scale \<134 points * gait freezing "on" medication * dysarthria of \> 2 in the item of the MDS-UPDRS III \[item #3.1\] * less than 50% improvement of axial score in the acute levodopa challenge test \[axial score = sum of items 3.1, 3.9, 3.10, 3.12, 3.13 of the MDS UPDRS III\] * Starkstein apathy score of ≥14 * Complete baseline PDQ-39-SI and patient diary available * written informed consent Exclusion Criteria: * Age \> 85 years * surgical or medical contraindications * abnormalities on brain MRI that preclude the implantation of electrodes into the GPi * contraindication for 3T MRI (baseline imaging) * severe medical illness that is likely to hamper the benefit of DBS * severe personality disorder that may interfere with optimization of DBS * dementia according to DSM-V and MMSE \< 20 * ongoing psychosis (except pseudohallucinations) * ongoing major depression (BDI-II \> 23) or depression of any severity with suicidal ideation