 Study design: A quadripolar SCS-lead Quad-plus, Medtronic Inc., Minnesota, USA was implanted via a percutaneous puncture at the Th1112 level of the dorsal epidural space in local anesthesia with the patient in the prone position. The electrode is advanced to the mid-thoracic level, aiming for a final position around T6-T8, until intraoperative stimulation yields paresthesias covering the abdomen . The electrode is then connected to an impulse generator Itrel-3, Medtronic Inc. implanted subcutaneously in the upper left quadrant of the abdomen. Stimulation frequency will be set to 50 Hz for all patients but other parameters electrode pole combinations, amplitudes and pulse width are adjusted and set to produce adequate paresthesias of comfortable intensity. 