Understanding the influence of pain and spinal cord stimulation on evoked potentials and EEG.

Rationale:

In patients with severe chronic (neuropathic) pain, spinal cord stimulation (SCS) is an option. However, even after careful selection of patients, not in all patients pain is relieved by at least 50%. The cause of this is unknown. However, recently a new stimulation method is developed (burst, a software setting) of which it is claimed that is relieves pain better than conventional (tonic) SCS and it would elicit no or less paresthesias. The working mechanism and effects of tonic SCS are partly known, but burst stimulation is not studied yet. By studying patients in tonic, burst and no SCS and controls without pain, knowledge of the effects of SCS and pain on the brain can be obtained. Measurements in tonic and burst stimulation have already been performed in 19 patients and about 21 patients will follow.



Objective:

The primary objective is to find out whether there is enhanced processing of sensory stimuli when people are in pain and to find out whether SCS has influence on the processing of sensory stimuli applied on non painful body parts. We focus on the activity of the primary somatosensory cortex (S1). Secondary objectives are to assess how SCS and pain modulate the activity of other brain areas and to identify a possible pain network. We will also assess this in measurements of EEG in rest. The influence of the presence of paresthesias, allodynia and kind of pain on evoked potentials (EPs) and the EEG will be assessed. The last objectives are to put the pain scores during the trials of burst stimulation in the perspective of the pain scores that patients have in the case they have no stimulation and to assess the prognostic value of EPs and EEG for the success of (burst) stimulation.



Study design:

The study is a prospective pilot study in which all patients that had a period of burst stimulation and in whom already measurements are performed are included. Therefore we will have repeated measurements of the patients. As controls, subjects without pain are included.



Study population:

The patients that will be included are the same patients that already underwent burst stimulation and EP and EEG measurements, which are 40 patients. They are all adults. The control group consists of 20 volunteers without chronic pain. This group will be aged-matched to the patients.



Intervention:

The patients are asked to turn off their stimulator 12 hours before the measurements and keep the stimulator off until the measurements are performed. For the control group there is no intervention.



Main study parameters/endpoints:

The main study parameters are the amplitudes of the reconstructed signal of the S1 evoked by stimulation of Aβ-fibers and Aδ-fibers and pain scores, determined by a visual analog score (VAS). These amplitudes and pain scores will be compared in tonic SCS, burst SCS, SCS off and controls.

In chronic pain the processing of sensational and painful stimuli will be disturbed. In patients with effective spinal cord stimulation the processing will normalize.

N/A

The patients are asked to turn off their stimulator 12 hours before the measurements and keep the stimulator turned off until the measurements are performed. For the control group there is no intervention.