After a run-in period of 4 months during which a prospective assessment of healthcare resources utilization and of the severity of the symptoms will be obtained, patients will be implanted. The follow-up period after implantation of the device will last 24 months in every patients and will be divided in two parts: a) After the first postoperative month during which the device will remained on the "OFF" position, the first phase of the study will be a randomized double-blind cross-over study with 2 periods of 4 months during which the device will be activated or not. After the 9th month of follow up, the trial will be an open trial and the device will be activated in all patients.