inflammatory low back pain model

Inflammatory Back Pain? A look deeper with this research

The study explores the correlation between MRI features in paraspinal muscles, inflammatory processes, and back pain in patients with lumbar disc herniation.1

 

Paraspinal muscles, including psoas, multifidus muscle (MM), and erector spinae muscle, are crucial for the stability and functional movements of the lumbar vertebral column. Recent studies have shown structural changes in paraspinal muscles, such as increased fatty infiltration, reduced cross-sectional area (CSA), and fibre-type transformation, in association with intervertebral disc degeneration, such as lumbar disc herniation (LDH), which may contribute to low back pain (LBP). Disuse, denervation, and dysregulation of the inflammatory state have been identified as the main mechanisms for these changes.

 

Dysregulation of local inflammatory activity has been suggested as a novel mechanism to explain fat and connective tissue accumulation in paraspinal muscles. Inflammation processes lead to the loss of slow-twitch muscle fibres, connective tissue accumulation, and fatty infiltration. Previous studies have observed structural remodelling of paraspinal muscles in patients with LDH, which is closely related to high-intensity pain and disability. However, there are some controversies about the mechanisms that regulate paraspinal muscle structural changes associated with or without LBP in patients with LDH.

 

A recent human study supported that fatty infiltration of MM is associated with inflammatory dysregulation. However, the potential links between the dysregulation of the inflammatory state and structural changes in the paraspinal muscles in patients with LDH remain unclear. Further research is needed to confirm the mechanisms for structural remodeling in paraspinal muscles in patients with LDH.

inflammatory low back pain model

Methods of the Study

 

This prospective study involved 166 participants diagnosed with lumbar degeneration (LDH) and 80 healthy controls. The study assessed and screened participants from January 2020 to May 2022. The first stage focused on the relationship between pain and morphological changes in paraspinal muscles in patients with LDH. The second stage enrolled participants into two groups based on the presence of LBP, assessing the structural changes in paraspinal muscles between LBP and non-LBP groups. The third stage involved participants who underwent percutaneous endoscopic lumbar discectomy (PELD) surgery and investigated the associations between inflammatory marker expression and structural changes in paraspinal muscles in LDH patients with and without LBP.

 

The study included patients aged ≥18 years old, with a single level herniation disc on MRI, consistent clinical history and physical examination, and conservative treatment inefficiency for more than 3 months. Exclusion criteria included history of lumbar spine surgery, tumor, infection, spinal deformity, cauda equina syndrome, hormone use, diabetes, systemic metabolic bone disease, lipodystrophy, severe organic disease, neuromuscular syndromes, physical exercise or rehabilitation, and refusal to participate in the project. Demographic data included age, sex, BMI, duration of symptoms, and surgical level.

 

The study evaluated back pain and leg pain using the Visual Analogue Scale (VAS) and the Oswestry Disability Index (ODI) score. Three sequences of MRI were performed using a 3.0 T Trio Tim scanner, including sagittal T2-weighted fast spin-echo (FSE), sagittal T1-weight FSE, and axial T2-weighted scans. The total time taken for MR imaging ranged from 20 to 25 minutes.

 

The Pfirrmann score was used to evaluate IVD degeneration, with scores ranging from 0-10% to >50% fat and fibrous tissue within the muscle. Participants were divided into low and high fat infiltration groups based on their fat infiltration.

 

The software ImageJ was used to measure total and functional CSAs and fatty degeneration of paraspinal muscles. Total CSAs were referred to as the total area of muscle and fat, while functional CSA was fat-free in the area of paraspinal muscles. The ratio of functional CSA to total CSA was used to assess fatty degeneration.

 

The study aimed to assess the functional and fatty degeneration of paraspinal muscles using various imaging techniques. The total area of muscle and fat was referred to as the total area of muscle and fat, while the functional CSA was fat-free.

 

Discussion

 

This prospective study found a relationship between quantitative changes of paraspinal muscles and inflammatory dysregulation in patients with spinal cord disease (LDH). The study found that LDH patients had reduced CSAs of MM and functional CSA of MM, higher incidence rate of fatty degeneration in MM compared to healthy control subjects, higher presence of fatty degeneration in MM in LDH patients with LBP versus the patients without LBP, and upregulation of greater pro-inflammatory response in the MM in individuals with high-fat infiltration. These findings have potential implications for understanding the mechanisms that regulate MM structural changes in association with LBP in LDH patients.

 

Past studies have supported the potential relationships between structural changes in paraspinal muscles and the presence of LBP, leg pain, and functional limitation, especially in MM and erector spinae. However, paraspinal muscle dysfunction as a primary cause of LBP remains controversial. Previous reviews showed a positive association between paraspinal muscle characteristics and LBP, including CSA (50%) and fat infiltration (67%) in MM.

 

The study provided evidence for the reduced CSA and fatty degeneration of MM in the disc herniation-related LBP group. MM is considered an important part for stabilize and control of spine motion, and fat infiltration and the size of CSA are related to muscle activity and muscle strength, respectively. Therefore, an investigation of the mechanisms that regulate MM structural changes in association with LBP in LDH patients is required.

 

Dysregulation of local inflammatory activity has been proposed as a novel mechanism for the explanation of structural changes in MM. The data showed that expression of the pro-inflammatory cytokine TNF-α was elevated in MM in LDH patients with high-fat infiltration and reduction in the CSA, and expression of TNF-α was correlated with LBP. Adipose tissue is the main source of proinflammatory cytokines, which plays an important role in a range of muscle pathologies.

 

Inflammatory markers change in MM in this study provided evidence for translating the findings from recent animal studies to humans. Upregulation of TNF-α and IL-1β expression is associated with pain intensity, functional disability, and LBP chronicity, which was confirmed by recent studies.

Conclusion

 

The study reveals that patients with lower back pain (LDH) show reduced CSA and increased fatty infiltration in paraspinal muscles, linked to inflammatory regulation. The inflammatory response in the MM, mediated by TNF-α, promotes chronic pain and structural changes in paraspinal muscles, providing insight into the pathophysiology of LBP changes and initial evidence.

 


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