Nerve Fiber Activation in Neuropathic Pain

Descrizione riassuntiva dello studio

Approximately 8% of people suffer from nerve pain, and up to 15% of patients who have undergone surgery experience pain after the operation. Pain often significantly affects the daily lives of those affected. The treatment of such pain is very challenging, partly because the underlying mechanisms are not fully understood. In this study, we aim to directly investigate the sensitivity of the nerve fibers causing pain in you. Until now, the sensitivity of nerve fibers has been tested with very short and intense electrical pulses. In this project, we use slowly increasing electrical stimuli applied with very low intensity but lasting longer. According to our preliminary results, these electrical stimuli are much better suited to activate the "pain nerves". Therefore, we hope that with this method we can better capture a possible hypersensitivity of the "pain nerves", which could be the cause of your chronic pain. If we succeed, we would have an examination procedure available that could reveal the cause of pain in a subgroup of patients with chronic pain. For these patients, there may be a very good chance that a local treatment with a painkiller through the skin is promising. This examination procedure could therefore also be of great importance for easily verifying the effectiveness of these local therapies in the treatment of chronic pain. For the group of subjects with painful scars after surgery, we also want to investigate the sensitivity of the scars to various natural stimuli (touch, temperature). Such measurements are already recommended and used for various other patient groups with pain. This project will be conducted according to the laws in Switzerland. The responsible ethics committee has reviewed and approved this project.

(BASEC)

Intervento studiato

The investigations will be conducted in one day. First, a physical examination will be performed by a neurologist (approximately 60 minutes). This will be followed by a measurement with electrical stimuli and the determination of skin blood flow (approximately 30 minutes).

For patients with pain in the area of the surgical scar, additional measurements will be performed to determine the threshold of sensation to natural stimuli (touch, temperature) and nerve conduction velocity (approximately 2 hours).

Finally, in both groups, a pain patch will be applied to the skin of the painful body area.

Description of individual measurements:

1. Determination of sensitivity to a single electrical stimulus with sinusoidal waveform

The electrical stimulation is completely safe and approved for humans. Through 2 small wires held on the skin, single stimuli with an intensity of 0.2 – 0.4 – 0.8 – 1 mA will be given. The highest stimulus strength corresponds to the current with which conventional mobile phones are charged (1 milliampere, mA). We will always start with the lowest stimulus strength (0.2 mA), which you will probably not feel, and then increase the stimulus strength in such small steps that only a slight increase in sensation strength is expected. The strongest intensity (1 mA) may be perceived as a slight prick, tingling, or burning. Please indicate the intensity of the sensation on a numerical scale from 0 (no pain) to 10 (maximum imaginable pain). The examination will be conducted in the painful and a non-painful body region and will take approximately 10 minutes in total.

2. Determination of sensitivity to repeated electrical sinusoidal stimuli

For this, 10 electrical stimuli will be given through 2 small wires held on the skin (see above). The stimuli are initially so weak (0.05 mA) that they are not felt. Then, the current will be slightly increased (0.1 – 0.2 – 0.4 mA) and the intensity of your sensation will be queried (numerical scale from 0 to 10, see above). The lowest intensity (0.05 mA) will be perceived as a light touch, the highest intensity (0.4 mA) may be felt as a slight prick or burning. Subsequently, we will apply the current intensity that you perceived as just painful for 1 minute and regularly query the pain intensity (numerical scale from 0 to 10, see above). This examination will be conducted in the painful and a non-painful body region and will take approximately 20 minutes in total.

3. Determination of local blood flow changes after electrical stimulation with laser method

In this method, a laser point scans the skin without contact and pain. A color-coded image of the skin blood flow is created, which will be evaluated after the examination. The quality of the image capture, and thus the validity of the image evaluation, is particularly sensitive to movements. Therefore, we will fix the examined body region during the examination in a padded vacuum cushion.

4. Pain patch

Finally, a patch with a painkiller (local anesthetic) will be applied to the painful body site, and you will be asked to inform us of any changes in your pain sensation by phone the next day.

Further measurements for the group with pain at the surgical scar:

LEP (Laser-evoked potentials)

Through a laser method, pain sensations are triggered to measure the conductivity and conduction velocity of pain fibers. For this, brain currents are measured to see when the pain stimulus arrives in the brain.

QST (Quantitative Sensory Testing)

In QST, different nerve fibers of the skin are tested against natural stimuli to detect changes in temperature, pressure, pain, and touch perception.

(BASEC)

Malattie studiate

Patients with neuropathic pain and patients with chronic postoperative pain in the area of the surgical scar

(BASEC)

Sponsor

Gunther Landmann

(BASEC)

Nome del comitato etico approvante (per studi multicentrici solo il comitato principale)

Commissione d'etica svizzera nord-ovest/centrale EKNZ

(BASEC)

Data di approvazione del comitato etico

09.02.2017

(BASEC)

Risultati dello studio