Spinal cord and peripheral nerve stimulation (SCS/PNS) may alleviate chronic pain; however, the underlying mechanisms remain controversial. The aim of this observational study was to assess sensory changes in the ON-conditions and OFF-conditions to obtain insights into the mechanism of analgesic effects of SCS/PNS.
We contacted 85 patients and selected 28 patients with sufficient pain relief by SCS (n=15) or PNS (n=13) to assess their ongoing pain intensity (Numerical Rating Scale, 0 to 10), pain thresholds using Quantitative Sensory Testing (DFNS-protocol), and conditioned pain modulation (CPM) in a nonrandomized manner 2 to 4 hours after SCS/PNS deactivation (OFF-condition) and during stimulation (ON-condition). For each patient, the number of abnormally decreased pain thresholds, the presence of dynamic mechanical allodynia, and/or increased pain sensitivity was additionally totaled OR summed.
In the ON-condition, pain intensity decreased (Numerical Rating Scale SCS: 6.5±2.1 vs. 3.7±2.3, P<0.01; PNS: 6.2±1.4 vs. 4±1.9, P<0.01), but this did not correlate with any single sensory parameter. However, for SCS, the total number of parameters indicating hyperalgesia was significantly reduced in the ON-condition (45 vs. 23, P=0.001). A smaller CPM effect in the OFF-condition correlated with a greater CPM improvement during stimulation (SCS: r=−0.741, P=0.002; PNS: r=−0.773, P=0.003), independently from the spontaneous pain intensity.
The analgesic effect of SCS/PNS did not correlate with changes of single sensory parameters, but SCS/PNS reduced the number of abnormal hyperalgesic findings disregarding the kind of applied stimuli, suggesting a general antihyperalgesic effect. In addition, stimulation improved the endogenous pain inhibition. Both findings indicate that SCS/PNS may modulate central circuits.
*Department of Anaesthesiology, Intensive Care Medicine, Palliative Care Medicine and Pain Management, Medical Faculty of Ruhr-University, Berufsgenossenschaftliches Universitätsklinikum Bergmannsheil GmbH Bochum
†Department of Pain Medicine
∥Department of Neurology, Ruhr-University Bochum, BG-Kliniken Bergmannsheil, Bochum, Germany
‡Department of Neurology, Charité University Medicine Berlin, Berlin, Germany
§Pain Research, Department of Surgery and Cancer, Imperial College, London, UK
C.H.M.-F and T.W.: contributed equally.
The manuscript is part of T.W.’s doctoral thesis.
C.H.M.-F: drafted the manuscript. T.W.: collected the data, drafted the manuscript, and carried out the statistical analyses. L.E.: participated in drafting the manuscript. C.M.: responsible for the concept. T.M.: drafted the ethical proposal. J.V.: carried out the statistical analyses. E.K.E-K: responsible for the concept, gave advice, and made revisions.
The authors declare no conflict of interest.
Reprints: Christine H. Meyer-Frießem, Dr.Med., Department of Anesthesiology, Intensive Care Medicine, Palliative Care Medicine and Pain Management, BG Universitätsklinikum Bergmannsheil gGmbH, Bürkle-de-la-Camp Platz 1, Bochum 44789, Germany (e-mail: email@example.com).
Received May 31, 2018
Received in revised form September 7, 2018
Accepted September 15, 2018