• Primary endpoint will be the optimal parameters of PPN-DBS, defined as those leading to the best improvement of posture, balance and gait disturbance [ Time Frame: at day 0, day 7, 6 months, year 1 and year 2 ] [ Designated as safety issue: Yes ]
  

• Efficacy of PPN-DBS on disturbance of posture, balance and gait [ Time Frame: at day 0, day 7, 6 months, year 1 and year 2 ] [ Designated as safety issue: Yes ]
  
• Long term tolerance will be assessed by general and neurological examination, neuro-psychological tests (MMS, Mattis-DRS, Score fontal, BREF, MADRS) and by assessment of adverse events; [ Time Frame: at day 0, day 7, 6 months, year 1 and year 2 ] [ Designated as safety issue: Yes ]
  
• the components of gait that are most improved by PPN-DBS will be determined using computer-based systems (GAITRite and VICON); [ Time Frame: at day 0, day 7, 6 months, year 1 and year 2 ] [ Designated as safety issue: Yes ]
  
• evaluation of unilateral versus bilateral stimulation will be done during the double-blind assessment of all efficacy criteria; [ Time Frame: at day 0, day 7, 6 months, year 1 and year 2 ] [ Designated as safety issue: Yes ]
  
• effects of PPN-DBS on other PD symptom will be assessed using UPDRS and Hoehn and Yahr's staging; [ Time Frame: at day 0, day 7, 6 months, year 1 and year 2 ] [ Designated as safety issue: Yes ]
  
• the impact of PPN-DBS on quality of life and activities of daily living will be assessed by UPDRS II, SF36 and PDQ39 questionnaires and by a global satisfaction scale. [ Time Frame: at day 0, day 7, 6 months, year 1 and year 2 ] [ Designated as safety issue: No ]
  

Parkinson's disease (PD) is a neurodegenerative disorder with an association of akinesia, rigidity and tremor, but also so-called "axial" motor signs (disturbance of posture, gait and balance) that usually appear after several years of disease evolution. These axial signs, generally resistant to drug treatment and deep brain stimulation (DBS) of subthalamic nucleus (STN), can generate a loss of autonomy and traumatic complications due to frequent falls. An improvement of axial signs by DBS of the pedunculo-pontin nucleus (PPN) has been described for a small number of patients. Nevertheless, this effect needs to be confirmed in more patients and there is need for complementary knowledge, including optimal stimulation modalities.

The primary objective of the current prospective monocentric pilot study is to determine the optimal stimulation parameters (site of stimulation, frequency, amplitude) of PPN-DBS in patients with severe PD. Secondary objectives are 1) to confirm the effect of PPN-DBS on disturbance of posture, balance and gait; 2) to evaluate long term tolerance of this technique; 3) to determine the components of gait that are most improved by PPN-DBS; 4) to evaluate unilateral versus bilateral stimulation; 5) to evaluate the effects of PPN-DBS on other PD symptoms; 6) to determine the impact of PPN-DBS on quality of life. Five patients fulfilling the following criteria, will be included: age between 18 and 70 years, idiopathic PD for more than 5 years, predominant axial motor signs (disturbance of gait and balance, falls, freezing of gait) responsible for disability in daily living and resistant to optimal treatment. The DBS electrodes (model 3389, Medtronic) will be stereotactically implanted bilaterally in the PPN, according to the technique usually used for STN-DBS, and connected to the subcutaneously implanted stimulator (Kinetra, Medtronic). After the surgery, the study will comprise two phases: a 6-month phase dedicated to optimisation of the stimulation parameters (including systematic evaluation of defined parameters); followed by a phase of evaluation, that will compare, in a double-blind setting, 4 conditions (right unilateral, left unilateral, bilateral and off stimulation). Efficacy of PPN-DBS will be evaluated by clinical rating scales quantifying motor disturbance, cognitive function and quality of life, and by the means of computer-based measure of gait and balance (system Gaitrite and Vicon). Expected results are 1) an improvement of gait, postural and balance disturbance, due to PPN-DBS. 2) Identification of the optimal PPN-DBS parameters, improving most the axial PD symptoms, will allow to abbreviate the adjustment period, by using as default setting these parameters when turning on the stimulator for the first time; 3) Identification of the axial signs which are the most improved will allow to select patients that could most benefit from PPN-DBS 4) The use of diverse specific rating scales and quantitative gait analysis will allow to determine the most relevant clinical criteria to be evaluated in further studies. Thus, this project will allow to obtain data (selection criteria, relevant rating scales, optimal stimulation parameters) mandatory for the construction of further comparative large-scale studies, if the efficacy of PPN-DBS was confirmed by the present study.