Towards Whole Person Health: Investigating the Gut-Brain Axis and Low Back Pain in People with Symptomatic Lumbar Spinal Stenosis Using a Traditional Indian Medicine Informed Theory Model

Abstract

Lumbar spinal stenosis (LSS) is a degenerative spinal condition common in older adults and is characterized by the narrowing of the spinal canal. People with this condition can experience leg pain and lower back pain and symptoms related to nerve compression, such as neurogenic claudication, including pain or numbness, tingling, weakness, or heaviness in the legs, called symptomatic LSS. While narrowing of the spinal canal is used for clinical decision making, associations between anatomical findings and clinical symptom severity are inconsistent. Evidence suggests the importance of investigating factors other than their anatomical findings. One of the candidate factors influencing their pain and disability is the gut-brain axis. The gut-brain axis is a bidirectional network between the gut and brain, and evidence suggests that there is a relationship with chronic pain and spinal conditions. The findings from traditional medical practices and cross-sectional studies suggest gut dysfunctions, such as constipation, might be associated with chronic pain. Few studies have investigated whether the dysfunctions in the gut-brain axis influence chronic low back pain experiences, specifically among people with a specific spinal pain condition with anatomical pathology, such as LSS. Therefore, we investigated the associations between the dysfunction of the gut-brain axis, measured through 1) disorders related to gut-brain axis (presented in Chapter 1) and 2) gut dysfunction symptoms, and chronic pain-related experiences (presented in Chapter 2) among individuals with symptomatic LSS. Given the limited number of human studies showing which gut dysfunction symptoms may be relevant in spinal pain, we used a theory-guided approach to inform our hypothesis generation and predictor selection. We integrated the interpretations of ancient manuscripts with expert opinions of Traditional Indian Medical Systems (Siddha and Ayurveda) and developed a theory-informed conceptual model describing how the gut dysfunctions manifest as measurable symptoms and affect chronic pain specifically in LSS to identify potential candidate predictors. In Chapter 1, we found those individuals with a history of Disorders of Gut-Brain Interaction (DGBI) or Inflammatory Bowel Disease (IBD) consistently reported higher pain and disability with lower physical function compared to those with no history over a year. However, importantly, we also found that DGBI/IBD was not associated with pain and disability, after we adjusted for demographic and mental health related covariates. In Chapter 2, we found constipation severity was significantly associated with all pain, functionality, and disability outcomes in both mixed effects and first difference models, both H before and after adjustment for covariates. There was a clinically important difference in estimates comparing moderate/severe vs no constipation on disability, LSS-specific symptom and function measures, and physical function . Conversely, stool consistency was not significantly associated with any outcomes. Overall, our study indicated associations between gut-brain axis and pain in LSS. Specifically, we found constipation was an independent factor for pain and disability. Those findings also aligned with Traditional Indian Medicine theories, and our study provides support to the value of integrating insights from Traditional Indian Medical systems to identify novel factors in chronic pain. Also, our findings provides support to bio-psycho-social model for LSS and DGBI/IBD to consider multiple demographic and mental health factors.