The role of mast cells in disc herniation inflammation

Smoking and tetramer tryptase accelerate intervertebral disc degeneration by inducing METTL14-mediated DIXDC1 m6 modification

Although cigarette smoking (CS) and low back pain (LBP) are common worldwide, their correlations and the mechanisms of action remain unclear. We have shown that excessive activation of mast cells (MCs) and their proteases play key roles in CS-associated diseases, like asthma, chronic obstructive pulmonary disease (COPD), blood coagulation, and lung cancer. Previous studies have also shown that MCs and their proteases induce degenerative musculoskeletal disease. By using a custom-designed smoke-exposure mouse system, we demonstrated that CS results in intervertebral disc (IVD) degeneration and release of MC-restricted tetramer tryptases (TTs) in the IVDs. TTs were found to regulate the expression of methyltransferase 14 (METTL14) at the epigenetic level by inducing N6-methyladenosine (m6A) deposition in the 3' untranslated region (UTR) of the transcript that encodes dishevelled-axin (DIX) domain-containing 1 (DIXDC1). That reaction increases the mRNA stability and expression of Dixdc1. DIXDC1 functionally interacts with disrupted in schizophrenia 1 (DISC1) to accelerate the degeneration and senescence of nucleus pulposus (NP) cells by activating a canonical Wnt pathway. Our study demonstrates the association between CS, MC-derived TTs, and LBP. These findings raise the possibility that METTL14-medicated DIXDC1 m6A modification could serve as a potential therapeutic target to block the development of degeneration of the NP in LBP patients.

Inflammation in the intervertebral disc herniation

Up until fairly recently, it was thought that sciatic pain in the lumbar herniated disc was caused by compression on the nerve root. However, the lumbar herniated disc shows mixed pictures which are difficult to explain by simple mechanical compromise. In recent years various immunology, immunohistochemistry and molecular biology studies have shown that the herniated tissue is not an inert material, but rather it Is biologically very active with the capability of expressing a series of inflammatory mediators: cytokines such as interleukin-1, interleukin-6, interleuquin-8 and tumor necrosis factor being the ones which stand out. The inflammation is not only induced by the chemical irritation of the bioactive substances released by the nucleus pulposus but also by an autoimmune response against itself. Thus, in addition to the mechanical factor, the biomechanical mediation plays an important role in the pathophysiology of sciatic pain and of radiculopathy. Through a review of a wide range of literature, we researched the cellular molecular mediators involved in this inflammatory process around the lumbar herniated disc and its involvement in sciatic pain.

The chondrodystrophic dog: A clinically relevant intermediate-sized animal model for the study of intervertebral disc-associated spinal pain

Low back pain (LBP) is the leading cause of disability worldwide, with an estimated 80% of the American population suffering from a painful back condition at some point during their lives. The most common cause of LBP is intervertebral disc (IVD) degeneration (IVDD), a condition that can be difficult to treat, either surgically or medically, with current available therapies. Thus, understanding the pathological mechanisms of IVDD and developing novel treatments are critical for improving outcome and quality of life in people living with LBP. While experimental animal models provide valuable mechanistic insight, each model has limitations that complicate translation to the clinical setting. This review focuses on the chondrodystrophic canine clinical model of IVDD as a promising model to assess IVD‐associated spinal pain and translational therapeutic strategies for LBP. The canine IVD, while smaller in size than human, goat, ovine, and bovine IVDs, is larger than most other small animal IVDD models and undergoes maturational changes similar to those of the human IVD. Furthermore, both dogs and humans develop painful IVDD as a spontaneous process, resulting in similar characteristic pathologies and clinical signs. Future exploration of the canine model as a model of IVD‐associated spinal pain and biological treatments using the canine clinical model will further demonstrate its translational capabilities with the added ethical benefit of treating an existing veterinary patient population with IVDD.

Mast Cell-Intervertebral disc cell interactions regulate inflammation, catabolism and angiogenesis in Discogenic Back Pain

Low back pain (LBP) is a widespread debilitating disorder of significant socio-economic importance and intervertebral disc (IVD) degeneration has been implicated in its pathogenesis. Despite its high prevalence the underlying causes of LBP and IVD degeneration are not well understood. Recent work in musculoskeletal degenerative diseases such as osteoarthritis have revealed a critical role for immune cells, specifically mast cells in their pathophysiology, eluding to a potential role for these cells in the pathogenesis of IVD degeneration. This study sought to characterize the presence and role of mast cells within the IVD, specifically, mast cell-IVD cell interactions using immunohistochemistry and 3D in-vitro cell culture methods. Mast cells were upregulated in painful human IVD tissue and induced an inflammatory, catabolic and pro-angiogenic phenotype in bovine nucleus pulposus and cartilage endplate cells at the gene level. Healthy bovine annulus fibrosus cells, however, demonstrated a protective role against key inflammatory (IL-1β and TNFα) and pro-angiogenic (VEGFA) genes expressed by mast cells, and mitigated neo-angiogenesis formation in vitro. In conclusion, mast cells can infiltrate and elicit a degenerate phenotype in IVD cells, enhancing key disease processes that characterize the degenerate IVD, making them a potential therapeutic target for LBP.

Elevated levels of tumor necrosis factor-α and TNFR1 in recurrent herniated lumbar discs correlate with chronicity of postoperative sciatic pain

BACKGROUND CONTEXT

Sciatica is a condition characterized by radicular pain that can be secondary to a lumbar disc herniation (LDH). More than 10% of patients report persistent pain after surgery. The underlying mechanisms of postoperative sciatica remain unclear. There is evidence demonstrating that inflammation plays a role in the pathophysiology of sciatica.

PURPOSE

The study aimed to assess if the expression of tumor necrosis factor (TNF)-α and its receptors (TNFR) was correlated with the severity of pre- and postoperative leg pain in LDH patients who underwent single or multiple decompressive discectomies.

SETTING

This is an experimental prospective human study of intraoperative intervertebral disc (IVD) samples, as well as a clinical scores evaluation.

METHODS

We analyzed the mRNA and protein levels of TNF-α, TNFR1, and TNFR2 in IVD biopsies, and correlated them with visual analogue scale (VAS) scores 1 day before surgery to 6 weeks and 6 months postoperatively.

RESULTS

We evaluated the correlation between the inflammation in IVD with pre- and postoperative pain scores after discectomy in LDH patients operated for the first time (fLDH, N=12) and for recurrent cases (rLDH, N=8). This analysis showed that TNF-α and TNFR1 mRNA levels were significantly greater in rLDH patients; there was a twofold increase for TNF-α and a 50% increase for TNFR1. Similarly, protein levels in IVD samples positively correlated with postoperative VAS scores, whereas TNFR2 protein levels negatively correlated with postoperative VAS scores.

CONCLUSIONS

These findings indicate that rLDH patients present higher postoperative VAS scores compared with fLDH patients, and also that these scores are correlated with increased inflammation and may contribute to pain chronicity.

Serum levels of the pro-inflammatory interleukins 6 (IL-6) and -8 (IL-8) in patients with lumbar radicular pain due to disc herniation: A 12-month prospective study

Earlier studies indicate that lumbar radicular pain after disc herniation may be associated with a local inflammation induced by leakage of nucleus pulposus (NP) into the spinal canal and neuroforamen. In the present study we addressed the role of two interleukins, IL-6 and IL-8 in such long-lasting lumbar radicular pain. All 127 patients were recruited from Oslo University Hospital, Ullevål, Norway. At inclusion, 6weeks and 12months, serum concentrations of IL-6 and IL-8 were analyzed by enzyme-linked immunosorbent assay (ELISA) and pain intensity was reported on a 0-10cm visual analog scale (VAS). Significantly higher levels of IL-6 and IL-8 in serum were found in patients with VAS ⩾3 at 12months, than in patient with VAS <3 at 12months (p⩽0.01, test of between-subjects effect, repeated measures ANOVA, covariates for IL-6: age, smoking; covariates for IL-8: smoking, treatment). For the first time we show that chronic lumbar radicular pain may be associated with a persistent increase of the pro-inflammatory substances IL-6 and IL-8 in serum after disc herniation.

Clinical significance of tumor necrosis factor-α inhibitors in the treatment of sciatica: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

Currently, no satisfactory treatment is available for sciatica caused by herniated discs and/or spinal stenosis. The objective of this study is to assess the value of tumor necrosis factor (TNF)-α inhibitors in the treatment of sciatica.

METHODS

Without language restrictions, we searched PubMed, OVID, EMBASE, the Web of Science, the Clinical Trials Registers, the Cochrane Central Register of Controlled Trials and the China Academic Library and Information System. We then performed a systematic review and meta-analysis on the enrolled trials that met the inclusion criteria.

RESULTS

Nine prospective randomized controlled trials (RCTs) and two before-after controlled trials involving 531 patients met our inclusion criteria and were included in this study. Our systematic assessment and meta-analysis demonstrated that in terms of the natural course of the disease, compared with the control condition, TNF-α inhibitors neither significantly relieved lower back and leg pain (both p > 0.05) nor enhanced the proportion of patients who felt overall satisfaction (global perceived effect (satisfaction)) or were able to return to work (return to work) (combined endpoint; p > 0.05) at the short-term, medium-term and long-term follow-ups. In addition, compared with the control condition, TNF-α inhibitors could reduce the risk ratio (RR) of discectomy or radicular block (combined endpoint; RR = 0.51, 95% CI 0.26 to 1.00, p = 0.049) at medium-term follow-up, but did not decrease RR at the short-term (RR = 0.64, 95% CI 0.17 to 2.40, p = 0.508) and long-term follow-ups (RR = 0.64, 95% CI 0.40 to 1.03, p = 0.065).

CONCLUSION

The currently available evidence demonstrated that other than reducing the RR of discectomy or radicular block (combined endpoint) at medium-term follow-up, TNF-α inhibitors showed limited clinical value in the treatment of sciatica caused by herniated discs and/or spinal stenosis.

The expression of tumor necrosis factor-α and CD68 in high-intensity zone of lumbar intervertebral disc on magnetic resonance image in the patients with low back pain

STUDY DESIGN

Several recent studies suggest a high-intensity zone (HIZ) within the posterior annulu of lumbar intervertebral disc seen on T2-weighted magnetic resonance (MR) images represents the inflammation in the annulus, an annular tear, and/or vascular granulation tissue. It has not be reported yet whether there is the expression of tumor necrosis factor (TNF-α) and inflammatory cells appear in HIZ of intervertebral disc on MR images.

OBJECTIVE

To study whether HIZ is a specific signal for the inflammatory reaction of painful intervertebral disc.

SUMMARY OF BACKGROUND DATA

The presence of HIZ signal within the posterior annulus seen on sagittal T2-weighted spin-echo magnetic imaging sequences has already been used in the diagnosis of painful annular tears in the last decade. There have been studies suggesting that the presence of HIZ reflects inflammation in the annulus, an annular tear, and/or vascular granulation tissue.

METHODS

Twenty-six consecutive patients with low back pain underwent MR images and discography (age range = 26-65 years; mean age = 47.5 years; 16 men, 10 women). In all the patients, HIZ appeared in the involved intervertebral discs on T2-weighted MR images. Lumbar discography was usually performed on each patient for the discs L3-L4, L4-L5, and L5-S1. All patients received posterior lumbar interbody fusion procedures. The intervertebral disc specimens contained HIZ were excised en bloc during posterior interbody fusion. The distribution of TNF-α and CD68 in the intervertebral disc specimens within HIZ on MR images from 26 consecutive patients with low back pain and in the intervertebral disc specimens from five fresh cadavers were observed.

RESULTS

The histologic study of the consecutive sagittal slices of the HIZ showed a lot of proliferated small round cells and fibroblasts. There were a lot of TNF-α positive cells and some CD68 positive cells in HIZ and the number of TNF-α and CD68 positive cells in HIZ was significantly higher than that in the annulus fibrosus around HIZ and in the control (P < 0.05).

CONCLUSION

The results of this study indicate that HIZ may be a specific signal for the inflammatory reaction of painful intervertebral disc.

Age-related variation in cell density of human lumbar intervertebral disc

STUDY DESIGN

changes in cell density of endplate (EP), nucleus pulposus (NP), and anulus fibrosus (AF) during ageing were systematically investigated in defined regions of interest in complete human motion segments.

OBJECTIVES

to elucidate cell density and total cell number in distinct anatomic regions of the intervertebral disc; to test effects of gender, level and age on cell density; and to correlate changes in cell density with histologic signs of disc degeneration.

SUMMARY OF BACKGROUND DATA

the available information on the cell density within intervertebral discs and its age-related changes is sparse. This knowledge, however, is a crucial prerequisite for cell-based tissue engineering approaches of the intervertebral disc.

METHODS

in 49 complete cross-sections from lumbar motion segments (newborn to 86 years) from 22 specimens, cell density was determined by the Abercrombie method in EP, NP, and AF, and total cell number was counted per region of interest.

RESULTS

cell density in EP, NP, and AF decreased significantly from 0 to 16 years with the main changes occuring from 0 to 3 years for NP and AF. No significant variations were observed thereafter. We found a significant correlation of cell density and histologic degeneration score between 0 and 1, but not for scores >1. Gender and disc level did not influence cell density.

CONCLUSION

This study provides data concerning the total number of cells in the various regions of the intervertebral disc for different age groups. This knowledge will be beneficial for cell-based treatment approaches, which may evolve in the future.

Expression of proteinase-activated receptor-2 in the intervertebral disc

STUDY DESIGN

Immunohistochemical and biochemical analyses of proteinase-activated receptor-2 (PAR-2) in rat and human intervertebral discs (IVDs).

OBJECTIVES

To examine the expression and function of PAR-2 in rat IVD cells, and to determine if PAR-2 is expressed in human IVDs.

SUMMARY OF BACKGROUND DATA

PAR-2 is a G protein-coupled receptor that contributes to the regulation of inflammatory reactions and the pathophysiology of inflammatory diseases, including arthritis. The expression of PAR-2 in the IVD has not been determined.

METHODS

PAR-2 expression by rat IVD cells and tissues was examined using immunohistochemistry and western blot. Rat anulus fibrosus cells in monolayer culture were used to examine the biologic role of PAR-2 in vitro. The effect of PAR-2-activating peptide (PAR-2AP) on the catabolic cascade was assessed by western blot and real-time PCR. The expression of PAR-2 by human IVD tissues at different stages of degeneration was determined by immunohistochemical analyses.

RESULTS

PAR-2 was expressed by rat IVD cells and in both anulus fibrosus and nucleus pulposus tissues, PAR-2 expression was up-regulated by interleukin-1beta (IL-1beta). PAR-2AP significantly increased the release of IL-1beta into the medium. Although PAR-2AP had no direct effect on matrix metalloproteinase-3 (MMP-3) and MMP-13 mRNA levels, treatment with PAR-2AP significantly up-regulated the mRNA levels of a disintegrin and metalloproteinase with thrombospondin motif-4. The simultaneous administration of PAR-2AP and IL-1beta synergistically up-regulated the mRNA levels of a disintegrin and metalloproteinase with thrombospondin motif-4, MMP-3, and MMP-13. The expression of PAR-2 was identified in human IVD tissues. The number of PAR-2-expressing cells was significantly elevated in advanced stages of IVD degeneration compared with those in early stages of degeneration.

CONCLUSION

Our results demonstrate for the first time that IVD cells express PAR-2. The expression of PAR-2 is regulated by IL-1beta stimulation. PAR-2 activation accelerates the expression of matrix-degrading enzymes. PAR-2 may play an important role in the cytokine-mediated catabolic cascade and consequently may be involved in IVD degeneration.

Innervation, inflammation, and hypermobility may characterize pathologic disc degeneration: review of animal model data

Animal models provide important clues to the pathomechanisms of human intervertebral disc degeneration. Previous reviews on this topic have highlighted the fact that loss of nuclear volume (and, consequently, pressure) is a common trigger for tissue-remodeling and anatomic change consistent with degeneration in humans. Unfortunately, a large gap still exists in the medical knowledge base that serves to distinguish symptomatic from asymptomatic degeneration. Because disc degeneration per se is not a basis for clinical intervention, identification of specific features underlying discogenic pain is of the utmost importance to advance the current level of care and identify novel therapeutic targets. This article presents animal-model evidence that pathologic, or painful, degeneration is characterized by ineffective injury-healing of peripheral tissue. Because the disc is only vascularized at the vertebral end plate and the outer part of the anulus, these are the likely sites for focal damage, inflammation, neoinnervation, and nociceptor sensitization. Consequently, while nuclear insufficiency is likely the root of degenerative change, the end plate and peripheral part of the anulus are more likely the source of patient discomfort.

Possible pathogenesis of painful intervertebral disc degeneration

STUDY DESIGN

We collected the specimens of lumbar intervertebral disc (i.e., the symptomatic degenerative disc) from patients with discogenic low back pain to study the histopathologic features and growth factor expressions.

OBJECTIVES

To study the pathogenesis of disc degeneration, meanwhile discriminating between common disc degeneration (aging disc) (i.e., black asymptomatic disc, not clinically relevant) and painful disc degeneration (i.e., symptomatic disc, clinically relevant).

SUMMARY OF BACKGROUND DATA

The pathogenesis of intervertebral disc degeneration is poorly understood, mainly because of the difficulty to establish the experimental model with good reproducibility. Recently, the popularity of spinal fusion leads to more opportunities to obtain disc specimens, which could be applied to explore the pathogenesis of disc degeneration with modern biologic techniques.

METHODS

There were 21 specimens of lumbar intervertebral discs from 15 patients with discogenic low back pain during posterior lumbar interbody fusion, 16 aging discs from patients without low back pain, and 10 normal discs as control collected for the study of their histopathologic features, as well as the expressions of basic fibroblast growth factor (bFGF) and its receptor (Flg), transforming growth factor-beta1 (TGF-beta1) and its receptor (TGF-betaRI) by immunohistochemistry. The distribution of macrophages and mast cells was also noted. Proliferating cell nuclear antigen was assessed to evaluate proliferating activities of disc cells.

RESULTS

The distinct histologic characteristic of the disc from the patient with discogenic low back pain was the ingrowth of vascularized granulation tissue along torn fissures, extending from the external layer of the anulus fibrosus into the nucleus pulposus. The immunohistochemical staining showed that there were strong expressions of bFGF and TGF-beta1 and their receptors, as well as a strong expression of proliferating cell nuclear antigen in the zones of granulation tissue in the painful discs. However, there were only weak expressions in the nongranulation tissue zones in the painful discs and aging discs, and no expression in the control discs. In addition, abundant macrophages and mast cells were found in the granulation tissue zones of painful discs but absent in the nongranulation tissue zones of painful discs or aging discs and the normal control discs.

CONCLUSIONS

The findings indicated that degeneration of the painful disc might originate from the injury and subsequent repair of anulus fibrosus. Growth factors, such as bFGF and TGF-beta1, macrophages and mast cells might play a key role in the repair of the injured anulus fibrosus and subsequent disc degeneration.

A fibronectin fragment alters the metabolism by rabbit intervertebral disc cells in vitro

STUDY DESIGN

A biochemical and gene expression study was conducted to determine the effects of the 30-kDa N-terminal fibronectin fragment (Fn-f) on the glycosaminoglycan content of nucleus pulposus (NP) explant cultures, and on the gene expression profile of NP cells in alginate culture.

OBJECTIVE

To determine the effects of Fn-f on NP cells in alginate culture and disc explant cultures.

SUMMARY OF BACKGROUND DATA

The macroscopic and histologic features of disc degeneration have been well described, but the molecular biology of disc degeneration remains poorly understood. Although fibronectin and fibronectin fragments are known to accumulate in degenerative discs, the role of fibronectin fragments on the degenerative process has not been elucidated. This study sought to define the effects of Fn-f on the expression of key matrix and degradative genes and on disc matrix proteins.

METHODS

New Zealand white rabbits discs were harvested. NP cells were either isolated and grown in alginate culture or cultured as explanted tissue. The cultured cells were exposed to 10 nmol/L, 100 nmol/L, and 1 micromol/L concentrations of 30-kDa N-terminal Fn-f or a control substance and then analyzed histologically, biochemically, and with gene expression studies.

RESULTS

Alginate-cultured NP cells maintained a histologic appearance and phenotypic expression pattern similar to disc cells in vivo. Exposure of these cells to Fn-f led to the up-regulation of the MMP-9, MMP-13, and Fas genes and the down-regulation of the Type II collagen and aggrecan genes. In explant culture, Fn-f exposure led to a 60% reduction in glycosaminoglycan content compared with controls.

CONCLUSION

Treatment of NP cells in vitro with Fn-f led to changes in matrix proteins and gene expression similar to those seen during disc degeneration in vivo. This supports a possible detrimental role of the N-terminal fibronectin fragment in degenerative disc disease.

Immunolocalization of phagocytic cells in normal and degenerated intervertebral discs

STUDY DESIGN

An immunohistochemical study on human autopsy lumbar intervertebral discs and surgical specimens was conducted.

OBJECTIVE

To investigate the presence of phagocytic cells within herniated and nonherniated disc tissue and its correlation with disc calcification and degeneration.

SUMMARY OF BACKGROUND DATA

Increasing knowledge is gathered on the molecular mechanisms of extracellular matrix degradation during the process of disc degeneration. However, the data available on the cells involved in this process are sparse.

METHODS

Three different study populations were investigated: 1) 31 midsagittal tissue slices (age range, 0-86 years) encompassing the complete motion segment were decalcified and stained with a monoclonal antibody against the lysosomal CD68 antigen; 2) 12 additional midsagittal (undecalcified) tissue slices from normal fresh cadavers were resin-embedded and used for colocalization of calcifications (Kossa staining) and CD68-positive cells; and 3) in 53 surgical disc specimens from 32 individuals undergoing lumbar surgical interventions, the abundance of CD68-positive cells was correlated with diagnostic groups and magnetic resonance image findings.

RESULTS

In the discs of fetuses, infants, and adolescents, no labeled cells were seen. However, CD68-positive cells were detected in the nucleus pulposus of all individuals with histomorphologic signs of disc degeneration, predominantly in discs adjacent to cleft formations. Morphologically, CD68-positive cells did not differ from nuclear chondrocytes. In the anulus fibrosus, CD68-positive cells were seen less frequently. In the resin-embedded specimens, CD68-positive cells were not associated with tissue calcifications. In most of the surgical specimens, positive cells in cluster-like arrangements were seen frequently, particularly in areas of vascular ingrowth.

CONCLUSIONS

This is the first study describing the abundant presence of CD68-positive cells in human nonherniated disc nucleus pulposus. The findings additionally suggests that these cells are not invaded monocytes or macrophages, but rather, transformed resident cells. It is assumed that these cells are involved in the phagocytosis of extracellular matrix, and that discal cells therefore promote disc degradation, ultimately leading to a loss of biomechanical properties.

Pathophysiology of inflammatory, degenerative, and compressive radiculopathies

In answering the patient's question regarding how treatments are likely to "help [her] herniated disc," the mechanical and chemical components of radiculopathy should be addressed. Focal disc abnormalities often can be observed in those without pain, and symptomatic discs can become asymptomatic. Disc lesions can resolve radiologically with time, and patients' symptoms can improve before their radiographs. The literature reviewed in this article suggests that the best opportunity to offer therapies that address the chemical component of injury might be in those patients with acute disc pathology. In the case of degenerative stenosis, gradually evolving mechanical stressors may comprise the primary component of injury. In other instances, patients with radiographic evidence of neural foraminal or lumbar central stenosis may become symptomatic secondary to a superimposed mechanochemical injury. Such stressors can include a focal disc protrusion, leaking nuclear material from an annular tear, or synovial fluid from an adjacent arthrotic zygapophyseal joint. In these patients, the successful treatment of the acute injury process might allow the affected neural elements to return to their state of accommodation in an environment of gradually evolving mechanical compromise. A growing body of literature has helped clinicians to better understand the mechanisms behind radicular disorders. As spine clinicians, we should strive to educate our patients so that they may become more knowledgeable consumers of spine care. As the components of radicular pathology are elucidated further, new biochemical therapies will likely evolve. Similarly, there will probably always be a subset of patients who will require mechanical decompression, and some of these individuals should be offered such treatment without delay. There may a time in the radicular injury process at which a window of opportunity for treatment begins to close. After this point, any therapy offered will not be as likely to result in a more complete symptomatic response. Patients with chronic radicular pain may have neural structural insults and an increased sensitivity of the somatosensory system. Clinicians should strive to avoid this end stage of neural injury, which is less reversible from a chemical or mechanical standpoint and may respond only to chronic pain management modalities.

Inflammatory cells, motor weakness, and straight leg raising in transligamentous disc herniations

STUDY DESIGN

Possible statistically significant relationships between inflammatory cells and either motor weakness or straight leg raising were determined.

OBJECTIVES

To look for any clinically relevant links between inflammatory cells in disc herniations and signs of radiculopathy.

SUMMARY OF BACKGROUND DATA

Many studies have during recent years shown a presence of various types of inflammatory cells in disc herniations, but their clinical relevance has been questioned. To be clinically relevant, a presence of inflammatory cells should show a clear relationship to clinical evidence of nerve root involvement. Macrophages repeatedly demonstrated in a high proportion of disc herniations studied are of particular interest. Their major role may be in disc herniations tissue resorption and not in sciatica.

METHODS

A total of 96 disc herniations, all transligamentous, were analyzed by immunohistochemistry for presence of macrophages, T or B lymphocytes, and activated T lymphocytes separately. From recorded patient data, motor weakness and straight leg raising data were compared with a presence or absence of abundant (+ = at least 20 cells in a group) inflammatory cells. When not abundant, inflammatory cells were classified as "only few cells" (+) and grouped together with "no cells" (-). Patients with or without motor weakness were compared. Straight leg raising was compared for a positive (at <70 degrees ) or a negative test, and separately using the median as cut-off value. Groups were compared by chi-square analysis with the level of statistical significance set at P<0.05.

RESULTS

None of the four inflammatory cell types showed any significant association with motor weakness. Nor was any association observed when comparing positive and negative straight leg raising. With the median (straight leg raising = 47.5 degrees ) as cut-off, only activated T cells showed a weak (chi2 = 4.40, P<0.05) relationship with tighter straight leg raising, but none of the other cell types did. Even when straight leg raising was < 47.5 degrees, three times more disc herniations lacked (n = 34) inflammatory cells than showed (n = 13) inflammation. In a subgroup of only sequestrated discs, the findings were similar. However, in the patients with a bilaterally positive straight leg raising (n = 25), the prevalence of at least one inflammatory cell type was much higher in sequestrated discs (80%) than in extrusions (33%). This may suggest more subtle interrelationships between type of disc herniation, straight leg raising, and inflammatory cells.

CONCLUSIONS

The results of this study do not support a clinically relevant role for disc herniation inflammatory cells in sciatica. For the cells to be clinically relevant, a strong relationship between a presence of inflammatory cells and either or both of motor weakness and a tight straight leg raising should have been observed. The authors conclude that macrophages, which have been demonstrated in a high proportion of disc herniations in previous studies, are probably more important for disc tissue resorption processes than for producing sciatica. Other types of inflammatory cells are more rarely observed and may have no clinical meaning at all. However, more subtle interrelationships, considering the various types of disc herniations, should be further explored.