INTRODUCTION:
Low back pain (LBP) is the leading cause of disability world-wide with more than 500 million people at one time significantly limited in their ability to undertake activities of daily living. The nature of LBP is varied at each individual level and complex at a systems level. At an individual level, it is hypothesized that pain is either generated via mechanical compression or chemical irritation via inflammatory biomarkers. Pain has been traditionally studied using a scalar measurement for its intensity, however, the nature of pain incorporates various descriptors and current research postulates LBP as a linear spectrum consisting of predominantly nociceptive on one end and neuropathic on the other. Nociceptive LBP (NoP) results from the activation of nociceptors which innervates many structures in the lumbar spine. Neuropathic LBP (NeP) is caused by a ‘lesion or disease of the somatosensory nervous system’. Traditionally, NeP and NoP have been regarded as discrete entities, primarily attributed to patho-anatomical abnormalities within the lumbar spine. However, it is increasingly evident that the nature of both pain classifications is multifaceted, encompassing a range of physical, biomechanical, chemical, and psychosocial factors. As such this study aims to address current shortcomings in the literature regarding LBP classification by (1) investigating whether there is a difference in pain severity, disability, quality of life, and sociodemographic factors between patients with NeP and NoP, (2) exploring associations between radiological findings on MRI and X-ray and NeP and NoP, and (3) elucidate associations between non-spinal comorbid conditions and NeP and NoP.
METHODS:
This study received approval from the Human Research Ethics Committee of the University of Wollongong (No. 2020/329) and the University of New South Wales (No. HC210096). The developer of the PainDETECT Questionnaire (PDQ) provided written approval for its use in this study, a score of 12 indicated NoP and 19 indicated NeP. A retrospective analysis of a prospectively collected database involving a cohort of adult patients (>18 years) presenting with chronic LBP (>3 months) to a tertiary spine clinic was conducted. Patients were excluded if they had a history of spinal surgery, were diagnosed with specific spinal pathologies (fracture, malignancy, infection, axial spondylarthritis, cauda equina syndrome), or were diagnosed with non-spinal conditions that present with neuropathic symptoms (diabetic neuropathy, complex regional pain syndrome, central nervous system disorders, peripheral neuralgia). Patient demographic, radiology, and comorbidity analysis is outlined in Figure 1. Independent t-test and Mann-Whitney U was used to analyze the difference in continuous and ordinal parameters, respectively. Pearson Chi-square was used to analyze the independence of association. A binary logistic regression model was used to analyze the confounding status of comorbid medical conditions to determine independent relationships between specific conditions and neuropathic pain.
RESULTS:
A total of 707 patients completed the PainDETECT questionnaire and were included in the study. 512 met the inclusion and exclusion criteria and were included in the analysis, of which 279 had completed MRI and X-ray images and 400 had completed comorbidity questionnaire information (figure 1). The NeP group had a lower mean age than the NoP group (5515.6 vs. 5917.8, p<0.05), there was no difference in gender between the groups. The NeP group had higher pain severity (8.01.5 vs. 5.82.3, p<0.001), higher disability (48.721.4 vs. 25.719.4, p<0.001), and lower quality of life (0.5620.26 vs. 0.2780.25, p<0.001) compared to the NoP group. Smokers and patients with no partner marital status were 2.4 (OR 2.373, 95%C.I. [1.319-4.266] and OR 2.384, 95%C.I. [1.390-4.092], respectively, p<0.01) times more likely to have NeP compared to NoP. Additionally, the NeP group were of lower income class (=-2.425, p<0.05). In the radiology study, patients with NeP had higher foraminal (U=18.962, p=0.002) and spinal stenosis (U=14.481, p=0.005) severity. A subgroup analysis of patients without stenosis also revealed that the NeP group had higher prevalence of disk bulge (96% vs. 78%, p=0.002), high-intensity zones (51% vs. 19%, p<0.001) and Pfirmann grade (U=11.321, p=0.020). In the comorbidity analysis, Patients with depression, rheumatoid arthritis (RA) and gastrointestinal disorders were 2.844 (Exp(B)=2.844, 95%C.I. [1.426-5.670], p<0.01), 2.726 (Exp(B)=2.726, 95%C.I. [1.183-6.283], p<0.05) and 2.847 (Exp(B)=2.847, 95%C.I. [1.473-5.503], p<0.05) times more likely to suffer NeP than NoP, respectively.
DISCUSSION:
NeP is associated with higher levels of disability and lower quality of life. Smokers, individuals with a no partner marital status, and individuals with a lower income class were more likely to suffer NeP rather than NoP. The study also reveals that NeP is associated with more severe neural compression, increased presence of discogenic disease and inflammatory disk severity. Additionally, NeP correlates with gastrointestinal conditions, rheumatoid arthritis, and depression, highlighting the potential involvement of the gut microbiome as a common factor linking non-spinal comorbidities. These findings emphasize the importance of individualized management plans tailored to the specific pain and medical profiles of patients, rather than relying on a one-size-fits-all approach. Furthermore, the detrimental impact of NeP on patient well-being underscores the need to represent pain on a nociceptive-neuropathic continuum to achieve more accurate differentiation of pain components and reduce unnecessary pharmacotherapy, imaging, and non-targeted surgical interventions.