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

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.

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 the measurements of the rest EEG. The influence of the presence of
paresthesias, allodynia and kind of pain on 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 evoked
potentials (EPs) and EEG for the success of (burst) stimulation.

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.

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.

Participating patients are asked to turn off their stimulator which probably
will increase their pain. However, patients are obliged to turn of the SCS when
they drive and most patients turn off the stimulator each night. When
measurements are in the morning the extra time they have turned off the
stimulator is small. The appointment will be coupled to a regular checkup. For
the controls there is no intervention, however they must travel to the Clinical
Neurophysiology department of the MST hospital. There, patients and controls
will undergo the EEG and EP measurements with a duration of about 20 minutes.
The measurements of the EEG and EPs are very well tolerable. Including
positioning of the EEG cap and preparation, the individual study duration will
be 1.5 hour. There is no individual benefit for the subjects participating in
the study. There are no health risks associated with the study, nor are there
any harmful aspects with respect to participating.