gms | German Medical Science

The treatment of chronic neuropathic pain can be difficult. In selected patients with treatment refractory pain and insufficient pharmacological therapy the indication for invasive methods has to be discussed. The chronic motorcortexstimulation on the opposite precentral gyrus seems to be effective in chronic neuropathic pain of the face or the upper and lower extremities, e.g. for phantom limb pain. In this prospective study we report ten cases with different neuropathic pain syndromes and the clinical results of contralateral motorcortexstimulation.

All patients suffered from chronic pain syndromes with neuropathic pain and any previous treatment including pharmacological therapy was ineffective. The location of the pain was unilateral regional like the face, forearm or one leg. All patients gave informed consent for a test trial with externalisation of the electrode cable and double-blind testing. Intraoperative a neuronavigation system with 3D-reconstruction of the cortical surface was used. In four cases data of functional MRI were matched with the neuronavigation. The recording of median or tibial nerve evoked potentials with phase inversion was performed via a four plate electrode. This electrode was also used for stimulation of the motor cortex. All operations were performed in local anaesthesia with a burr-hole approach over the central region. The electrode was placed epidural and connected with an externalisation device.

By using neuronavigation and intraoperative electrophysiology it was possible in all cases to identify and place the electrode over the precentral gyrus. Positive testing was defined as reduction of the visual analogue scale ≥50%. A positive test trial was performed in six of the ten patients and a stimulation device was implanted. In all patients we used sub threshold voltage of 2-6 volt in continuous or cyclic mode, an impulse width of 210-360 μsec and a frequency of 30-100 Hertz. In the other four cases a double blind test showed no differences in pain reduction with pseudostimulation and the electrodes were explanted. Complications like epidural haematoma were not observed. One wound infection over the connector of the extension cable was noted. In this case the device was temporary explanted and three months later reimplanted with the cable and the stimulation device on the opposite side. After this the positive effect and pain relief was present again.

Motorcortexstimulation is an alternative treatment option for a selected group of patients with neuropathic pain in well described areas like the face or extremities. By using a double-blind testing false positive, responders can become obvious and should not be implanted. Combination of neuronavigation and evoked potentials makes the placement of the electrode safer and easier.