gms | German Medical Science

Objective: Motor cortex stimulation (MCS) has recently been demonstrated to be an effective therapeutic option for patients with intolerable neuropathic pain. However, long term improvement of pain control is still unsatisfactory, and around 25% of the patients do not respond to MCS. Therefore we retrospectively analyzed our experience with MCS and – based on these findings – developed future approaches for optimizing this therapy.

Methods: Four patients with intractable unilateral neuropathic pain (average visual analog scale (VAS) score: 8) secondary to brachial plexus lesions (2 patients), thalamic stroke (1 patient) or brainstem stroke (1 patient) were selected for MCS. The motor cortex was anatomically located using stereotactic techniques based on preoperative MRI, and a 4-contact electrode (Medtronic Resume 2) was placed epidurally onto the motor cortex via a 6mm burr hole. Correct placement of the electrode was confirmed by intraoperative cortical stimulation. Postoperatively the therapeutic effect was tested via an external stimulator and in patients with a positive effect a permanent neurostimulator was implanted (Medtronic Itra III or Synergy). The patients were postoperatively followed-up for a period of up to two years, and improvement of pain was documented using the VAS scoring system.

Results: One patient did not report improvement of the pain by external stimulation and was excluded from long-term MCS. Three patients reported a significant positive effect of the external stimulation and underwent implantation of a neurostimulator. During the follow-up period adjustment of the stimulation parameters was necessary in one patient. All patients reported a significant improvement of the pain (average VAS score: 4) after implantation that persisted during the follow-up period.

Conclusions: In three of four patients MCS induced a significant improvement of pain control during the follow-up period. Virtual representation of changes in the spatial distribution of the current flow characteristics in relation to different stimulation parameters and improved methods for placement of the epidural strip electrode by functional MRI and frameless stereotactic techniques could improve MCS-therapy of neuropathic pain in the future. The development of a multifunctional strip electrode could be an important tool to investigate the electrophysiological mechanisms of cortical reorganization.