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

Deep brain stimulation (DBS) is an established treatment for advanced complicated Parkinson's disease (PD). Several controlled randomized studies have given proof of an advantage for operated patients as compared to medically treated patients in terms of motor outcome, activities of daily living and health status. However these studies have addressed mostly stimulation of the subthalamic nucleus (STN). GPi stimulation has not been compared to best medical treatment (BMT) in a prospective randomized controlled trial in patients with complicated PD who are not good candidates for STN stimulation. The investigators aim assessing GPi-DBS in patients with PD who have contraindications for STN-DBS.

The indication and excellent therapeutic effects of STN stimulation have been sufficiently proven in advanced PD, and the contraindications for this treatment are rather well established. Also, the observation that patients fulfilling the "STN-profile" but who had been operated for pallidal DBS and lost part of the treatment's benefit over time, improved when stimulated later in the STN (instead of the GPi) shows that patients qualifying for STN-DBS do not have as good a result with GPi-DBS.

GPi stimulation may be used in patients who do not qualify for STN stimulation. Especially postural instability, age over 70 years, and mild to moderate cognitive deficits are commonly considered to be exclusion criteria for STN stimulation but not for GPi stimulation. Therefore, the investigators propose a prospective randomized controlled trial of GPi stimulation in patients with PD and motor complications who have relative or absolute contraindications for STN stimulation.

Eligibility Criteria:
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