Substance P Level in Patients with Degenerative Lumbar Spine Disorder undergoing Decompressive Surgery: An Observational Study

Abstract

Introduction: Patients with degenerative lumbar spine disorders experience Chronic Low Back Pain (CLBP) for which they undergo decompressive surgery. Substance P (SP), a neurotransmitter which acts as a modulator of pain perception and transmits nociceptive signals via primary afferent fibers to the spinal cord and brainstem. In chronic painful conditions, SP level can be associated with the severity of pain and gets altered; however, this correlation is not present in acute pain. Aim: To evaluate serum SP level in CLBP patients undergoing decompressive spine surgery. Materials and Methods: The present study was a prospective observational study, in which 30 patients with CLBP undergoing decompressive spine surgery were enrolled. Along with them, one first-degree relative of each patient and an equal number of healthy volunteers were included in the study group. Patients were followed-up on the 5th postoperative day and at two months after surgery for the evaluation of SP levels and Visual Analogue Scale (VAS) scores. Statistical data analysis was carried out using IBM PASW Statistics (SPSS) 25.0 version software. SP levels followed a non normal distribution and were compared by Mann-Whitney U or Kruskal Wallis test (for 2 or more groups, respectively) and correlated using Spearman rank correlation. Results: Patients undergoing decompressive spine surgery had a significantly higher SP level (97.5 picogram/mL (pg/mL)) than healthy volunteers (23.22 pg/mL), p-value <0.001. The serum SP levels in patients were found to be significantly reduced on the 5th postoperative day (31.7 pg/mL) and at two months after surgery (48.5 pg/mL), p-value=0.043. In contrast, there was no discernible change in the VAS score, which did not correlate with the fall in SP levels on the 5th postoperative day. Conclusion: SP level was elevated in subjects with degenerative lumbar spine disorders undergoing decompressive surgery. Higher levels of SP can be attributed to CLBP in those patients. SP can be contemplated as a biomarker of pain due to degenerative lumbar spine pathology. However, further studies are warranted to substantiate this.