Correlation of Substance P Level in Blood and Cerebrospinal Fluid in Patients with Chronic Pain Syndromes: A Cross-sectional Study

Background: Substance P (SP), a neuropeptide identified in 1931, is ubiquitously present in both the central (CNS) and peripheral (PNS) nervous systems, playing a pivotal role in nociceptive signal transmission and immune system responses. Aims and Objectives: This research aims to explore the correlation of SP levels with chronic pain in various syndromes, specifically focusing on osteoarthritis (OA), rheumatoid arthritis (RA), widespread pain (WSP), and fibromyalgia (FM). Materials and Methods: This cross-sectional study involved 60 participants aged 18-65 years with chronic pain persisting for at least 180 days. Patient selection criteria included evaluation of pain severity using the Visual Analogue Scale (VAS). Substance P concentration was measured in both serum and cerebrospinal fluid (CSF). Statistical analysis methodologies employed included the t-test, ANOVA, and Pearson's correlation coefficient. All participants provided informed consent prior to their inclusion in the study. Results: The study population's features included a mean age of 42.08±10.57 years, with a gender distribution of 38 females and 22 males. Mean VAS scores were 73.5±13.0, while mean serumSP concentrations were 477.52±288.39 pg/mL and mean CSF SP concentrations were 653.95±262.23 pg/mL. Among the 60 patients classified with severe pain, 32 were diagnosed with osteoarthritis, 26 with rheumatoid arthritis, and 2 with widespread pain syndrome. Correlation analysis revealed a weak positive correlation between cerebrospinal fluid SP levels and chronic pain syndromes, and a moderate positive correlation with VAS scores. Weaker associations were observed between serum SP levels and both pain syndromes and VAS scores. These findings suggest potential influences of biomarkers on pain states and diagnostic categories. Conclusion: The study concludes that Substance P levels positively correlate with chronic pain perception across various pain syndromes. While SP levels do not appear to vary significantly with the specific underlying cause of chronic pain, these findings support the need for a larger, multi-centric trial to comprehensively assess SP's role in a more diverse patient population.