Nucleus pulposus-induced nerve root injury: relationship between blood flow and motor nerve conduction velocity

Neural-Immune Interactions: Implications for Pain Management in Patients with Low-Back Pain and Sciatica

Bidirectional communication between the immune system and the brain and the implications of this communication are emerging concepts in pain research. Although representing a small portion of the disc degeneration syndromes, lumbar herniated discs can cause significant symptoms that may persist even after surgical interventions. Evolving evidence demonstrates that proinflammatory cytokines are a key mediator in the process of disc degeneration as well as in the pain experienced by those afflicted with lumbar herniated discs. Activated immune cells release proinflammatory cytokines, which signal the brain through humoral and neural routes. The brain responds by altering neural activity and promoting further production of proinflammatory cytokines within the brain and spinal cord. Increased local cytokine production by disc tissue irritates spinal nerve roots, resulting in pain and functional changes in neural activity. This review of the current literature explores the importance of cytokine production within the context of lumbar disc degeneration and lumbar spine pain. Furthermore, the significance of the neural-immune interaction will be examined as it relates to pain management and to patient treatment.

Interleukin-23 may contribute to the pathogenesis of lumbar disc herniation through the IL-23/IL-17 pathway

BACKGROUND

Studies have indicated that interleukin 23 (IL-23) plays an important role in many inflammatory- and autoimmune-related diseases. However, there is little knowledge about IL-23 in lumbar disc herniation (LDH). Thus, in this study, we aimed to find out whether IL-23 is expressed in intervertebral discs (IVDs) and what roles it may play.

METHODS

Human IVD tissues were collected from 29 LDH patients and 8 vertebral fracture patients (normal control, NC group). According to the integrity of annulus fibrosus, LDH patients were divided into two groups: R group (ruptured group, n = 16) and NR group (non-ruptured group, n = 13). Morphological changes of IVDs were assessed by hematoxylin and eosin (HE staining), and expression of IL-23 in IVD tissues was detected by immunohistochemical staining. Besides gene expression of IL-23, IL-17, IL-6, IL-1β, and TNF-α was also evaluated by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

The results showed that the R group was more degenerated than the other two groups and NC group showed the least degenerated performance; stronger positive IL-23 expression was observed in herniated IVDs, especially in the R group. Meanwhile, higher gene expression of IL-23, IL-17, IL-6, IL-1β, and TNF-α was found in the tissues from LDH patients and a positive correlation between IL-17 and IL-23 gene expression was also observed.

CONCLUSIONS

Taken all above results together, it may be deduced that higher expression of IL-23 may contribute to the deterioration of IVDs through the IL-23/IL-17 pathway.

Role of interleukin-17 in chondrocytes of herniated intervertebral lumbar discs

Lumbar disc herniation (LDH) is a common cause of lumbosacral radiculopathy. An autoimmune response to a herniated nucleus pulposus (NP) has been suggested to play an important role in the initiation of radiculopathy. Interleukin-17 (IL-17) is a cytokine associated with inflammation and autoimmunity. The presence of IL-17 has been studied in patients with LDH; however, extensive investigation into the expression of IL-17 in different disc pathologies of LDH has not yet been conducted. The aim of the present study was to investigate the role of neovascularization and hypertrophic chondrocytes in herniated intervertebral lumbar discs. Fifty-two intervertebral lumbar disc specimens were extracted from 46 patients with LDH and were subsequently classified as either contained or non-contained disc herniation (CDH and NCDH, respectively). The specimens were stained with hematoxylin and eosin or toluidine blue, or were immunostained with polyclonal antibodies to IL-17 using the streptavidin-peroxidase method. The neovascular tissue and staining results were graded to establish the histological differences between the two herniation types. The intervertebral discs (IVDs) obtained from patients with NCDH showed significantly more neovascularization and granulation tissue than the discs obtained from patients with CDH (P<0.05). Furthermore, hypertrophic chondrocytes were more abundant in the NCDH specimens than in the CDH specimens (P<0.05). Similarly, the number of IL-17-immunoreactive cells was significantly higher in the NCDH specimens than that in the CDH specimens (P<0.01). In conclusion, local inflammation and autoreactive immune activation may play an important role in the pathogenesis of LDH. These results also suggest a role of chondrocytes in the repair of herniated IVDs.

Value of 3D MR lumbosacral radiculography in the diagnosis of symptomatic chemical radiculitis

BACKGROUND AND PURPOSE

Radiologic methods for the diagnosis of chemical radiculitis associated with anular tears in the lumbar spine have been rare. Provocative diskography is one of the methods for diagnosing diskogenic chemical radiculitis but is invasive. A reliable imaging method for replacing provocative diskography and diagnosing chemical radiculitis is required. Our aim was to investigate the value of 3D MR radiculography depicted by rendering imaging in the diagnosis of symptomatic chemical radiculopathy associated with anular tears.

MATERIALS AND METHODS

The study population consisted of 17 patients (age range, 32-88 years) with unilateral radiculopathy. Symptomatic chemical radiculopathy was confirmed with provocative CT diskography and/or provocative selective nerve root block for agreement of sides and levels. Through adhering to the principles of selective excitation (Proset imaging), we acquired 3D coronal FFE sequences with selective water excitation. Morphologic changes in the ipsilateral symptomatic nerve root caused by chemical radiculopathy were compared with those in the contralateral nerve root on 3D MR lumbosacral radiculography.

RESULTS

Pain reproduction at the contrast-leak level during diskography (n = 4) and selective nerve root injection (n = 13) showed concordant pain in all patients. All patients with symptomatic chemical radiculopathy showed nerve root swelling in both ipsilateral levels and sides on 3D MR radiculography. The most common nerve root affected by the chemical radiculopathy was the L5 nerve root (n = 13), while the most common segment exhibiting nerve root swelling was the exit nerve root (n = 16).

CONCLUSIONS

All patients with radicular leg pain caused by chemical radiculopathy showed nerve root swelling on 3D MR radiculography. We believe that in cases without mechanical nerve root compression caused by disk herniation or stenosis in the lumbar spine, nerve root swelling on 3D MR radiculography in patients with radiculopathy associated with an anular tear may be relevant in the diagnosis of symptomatic chemical radiculopathy.

Localization and function of insulin-like growth factor 1 in dorsal root ganglia in a rat disc herniation model

STUDY DESIGN

we investigated the localization of insulin-like growth factor 1 (IGF-1) using immunohistochemistry and the effects of small interfering RNA (siRNA) on IGF-1 in dorsal root ganglions (DRG) in a rat lumbar disc herniation (LDH) model.

OBJECTIVE

to determine the localization and function of IGF-1 in DRG of an experimental model of LDH.

SUMMARY OF BACKGROUND DATA

mechanical compression and chemical irritation are 2 major causative factors of radiculopathy in LDH. IGF-1, Ccnd1, Cdc2a, and CyclinA2 genes have been shown to be significantly upregulated in the mechanical model, but not in the chemical model. However, the localization and function of IGF-1 in DRG remain unknown in the mechanical compression animals.

METHODS

twenty-six adult female Sprague-Dawley rats were used in this study. A mechanical compression model was prepared by inserting a stainless rod. The rod was not inserted in the sham model. Expression of IGF-1 and Neuronal Nucli (NeuN) or glial fibrillary acidic protein was determined using double-fluorescence 7 days after mechanical compression (n = 5). Rats were randomly separated into 3 groups for the siRNA study (n = 7 in each group): (1) vehicle group; (2) siRNA group; and (3) sham group. The mechanical withdrawal threshold of the plantar food pad was examined using von Frey filaments for 35 days.

RESULTS

IGF-1 was localized particularly in the neuronal cell body, and revealed that it colocalized with NeuN but not with glial fibrillary acidic protein. The threshold was reduced in the vehicle and siRNA groups compared with the sham group. The threshold of the siRNA group significantly recovered from reduction compared with the vehicle group at 5 days after surgery, and this effect persisted throughout the experimental period. CONCLUSION.: IGF-1 was localized with neuronal cell bodies in DRG. IGF-1 knockdown caused a reduction in mechanical allodynia. The upregulation of IGF-1 might be a key factor in painful radiculopathy induced by mechanical factors.

Tumor necrosis alpha-blocking agent (etanercept): a triple blind randomized controlled trial of its use in treatment of sciatica

STUDY DESIGN

Triple blind randomized controlled study.

OBJECTIVE

To establish the treatment effect of etanercept in acute sciatica secondary to lumbar disc herniation.

SUMMARY OF BACKGROUND DATA

Etanercept is a selective competitor of tumor necrosis factor-alpha which is a proinflammatory cytokine. It is currently used alone or in combination with other medication for the treatment of chronic inflammatory disease.

METHODS

Inclusion criteria were acute unilateral radicular leg pain secondary to herniated nucleus pulposus confirmed on magnetic resonance imaging scan. Exclusions were previous back surgery, spinal stenosis and any contraindications to the use of etanercept such as immunosuppression. The patient, the injector, and assessor were blinded to the agent being used. Follow-up was at 6 weeks and 3 months posttreatment. Oswestry disability index and visual analog scores were among the assessment criteria.

RESULTS

Fifteen patients were recruited in a 4 years period with a 3 months follow-up of 80%. The etanercept group had 8 patients whereas the placebo group had 7. The average Oswestry disability index for the etanercept group preintervention was higher than that in the placebo group (53.6 vs. 50.4) and this remained the same after 6 weeks (46.1 vs. 31.2) and 3 months of follow-up (37 vs. 35). Visual analog score was also higher in the etanercept group versus placebo; preinjection (8.6 vs. 7.4), 6 weeks (5.0 vs. 3.8), and 3 months (4.8 vs. 4.5).

CONCLUSIONS

Small numbers of trial participants limited statistical analysis. The trend appears to show no benefit to the use of etanercept over placebo in the pharmacologic treatment of sciatica.

Effect of multi-planar CT image reformatting on surgeon diagnostic performance for localizing thoracolumbar disc extrusions in dogs

Accurate pre-operative localization and removal of disc material are important for minimizing morbidity in dogs with thoracolumbar disc extrusions. Computed tomography (CT) is an established technique for localizing disc extrusions in dogs, however the effect of multi-planar reformatting (MPR) on surgeon diagnostic performance has not been previously described. The purpose of this study was to test the effect of MPR CT on surgeon diagnostic accuracy, certainty and agreement for localizing thoracolumbar disc extrusions in dogs. Two veterinary surgeons and one veterinary neurologist who were unaware of surgical findings independently reviewed randomized sets of two-dimensional (2D) and MPR CT images from 111 dogs with confirmed thoracolumbar disc extrusions. For each set of images, readers recorded their localizations for extruded disc material and their diagnostic certainty. For MPR images, readers also recorded views they considered most helpful. Diagnostic accuracy estimates, mean diagnostic certainty scores and inter-observer agreement were compared using surgery as the gold standard. Frequencies were compared for MPR views rated most helpful. Diagnostic accuracy estimates were significantly greater for MPR vs. 2D CT images in one reader. Mean diagnostic certainty scores were significantly greater for MPR images in two readers. The change in agreement between 2D and MPR images differed from zero for all analyses (site, side, number affected) among all three readers. Multi-planar views rated most helpful with the highest frequency were oblique transverse and curved dorsal planar MPR views. Findings from this study indicate that multi-planar CT can improve surgeon diagnostic performance for localizing canine thoracolumbar disc extrusions.

Gait abnormalities and inflammatory cytokines in an autologous nucleus pulposus model of radiculopathy

STUDY DESIGN

The authors investigated gait abnormalities and mechanical hypersensitivity associated with invertebral disc herniation in a rat model of radiculopathy. Further evaluation involved assessing how nucleus pulposus (NP) injury affected systemic cytokine expression and molecular changes at the dorsal root ganglion (DRG).

OBJECTIVE

The objective of this work was to describe the gait and behavioral changes in an animal model of disc-herniation induced radiculopathy. A second objective included examining how these functional changes correlated with neuroinflammation and autoreactive lymphocyte immune activation.

SUMMARY OF BACKGROUND DATA

Animal models of radiculopathy describe demyelination, slowed nerve conduction, and heightened pain sensitivity after application of autologous NP to the DRG. The quantitative impact of disc herniation on animal locomotion has not been investigated. Further, while local inflammation occurs at the injury site, the role of autoimmune cytokines reactive against previously immune-sequestered NP requires investigation.

METHODS

NP-treated animals (n = 16) received autologous tail NP placed onto the L5 DRG exposed by unilateral facetectomy, and control animals (n = 16) underwent exposure only. At weekly time points, animals were evaluated for mechanical allodynia, thermal hyperalgesia, and gait characteristics through digitized video analysis. Serum cytokine content was measured after animal sacrifice, and immunohistochemistry tested DRG tissue for mediators of inflammation and immune activation.

RESULTS

Sensory testing revealed mechanical allodynia in the affected limb of NP-treated rats compared with sham animals (P < 0.01) at all time points. Gait analysis reflected functional locomotive consequences of marked asymmetry (P = 0.048) and preference to bear weight on the contralateral limb (duty factor imbalance, P < 0.01) at early time points. Equivalent serum cytokine expression occurred in both groups, confirming the local inflammatory nature of this disease model. Immunohistochemistry of the sectioned DRGs revealed equivalent postsurgical inflammatory activation (interleukin 23, P = 0.47) but substantial early immune activation in the NP-treated group (interleukin 17, P = 0.01).

CONCLUSION

This model of radiculopathy provides evidence of altered gait in a model of noncompressive disc herniation. Systemic inflammation was absent, but mechanical allodynia, local inflammation, and autoreactive immune activation were observed. Future work will involve therapeutic interventions to rescue animals from the phenotype of inflammatory radiculopathy.

Gene expression changes in dorsal root ganglion of rat experimental lumber disc herniation models

STUDY DESIGN

Comprehensive overviews of gene expression changes in dorsal root ganglion (DRG) were obtained using microarrays in 2 rat models of experimental lumbar disc herniation (LDH).

OBJECTIVE

To clarify the mechanisms of painful radiculopathy caused by LDH from the viewpoint of gene expression changes in DRG of 2 rat models of LDH.

SUMMARY AND BACKGROUND DATA

Mechanical compression and chemical irritation are considered to be the 2 major causative factors of radiculopathy associated with LDH. Several basic studies have revealed histologic and functional changes in the nerve root and DRG induced by mechanical compression or application of nucleus pulposus. However, the effects of the 2 major factors have not been investigated in detail. METHODS.: The effects of mechanical and chemical factors were assessed in 2 models and in sham-operated rats. The mechanical compression model had a stainless steel rod inserted through a drill hole in the L5 lamina; the nucleus pulposus model had autologous nucleus pulposus placed in the drill hole, and only a drill hole was made in the L5 lamina of sham-operated rats. Samples from the left L5 DRG were harvested from the models with mechanical allodynia and from sham rats and analyzed using microarrays at 3 and 7 days after surgery.

RESULTS

The gene expression profiles differed in the 2 models at 7 days, but were similar at 3 days after surgery. Expression of the growth factor gene, insulin-like growth factor 1, and of the cyclinD1, cell division cycle 2 homolog A, and cyclinA2 genes related to the cell cycle was significantly upregulated in the DRG of the mechanical compression group at 7 days after surgery.

CONCLUSION

Mechanical and chemical factors caused altered gene expression in the DRG at 7 days after surgery, suggesting that the mechanisms of nerve injury induced by these factors differ. The upregulation of IGF-1 might be a key factor in painful radiculopathy induced by mechanical factors.

Compensatory neovascularization after cauda equina compression in rats

STUDY DESIGN

An experimental study of compensatory neovascularization after cauda equina compression in rats.

OBJECTIVE

To explore the possibility that cauda equina compression induces compensatory neovascularization accompanied by an increase in the expression of vascular endothelial growth factor (VEGF).

SUMMARY OF BACKGROUND DATA

VEGF is a potent promoter of neovascularization that follows ischemia. Studies suggest that compression of the cauda equina causes ischemic changes that in turn cause an increase in VEGF expression that induces neovascularization. The mechanisms by which neovascularization develops in a compressed cauda equina are unknown.

METHODS

Two rectangular-solid pieces of silicone rubber were implanted in the fourth and sixth epidural spaces of rats (1 piece in each space); in the sham control group, no rubber was implanted. VEGF expression in the compressed cauda equina was assessed by immunohistochemistry and Western blotting. Ischemia and neovascularization of the cauda equina were assessed by immunostaining for hypoxia-inducible factor-1 alpha (HIF-1 alpha) and 5-bromodeoxyuridine (BrdU). The unpaired Student t test was used for statistical analysis (P < 0.05).

RESULTS

At 14 and 21 days after surgery, ischemic changes were observed, as indicated by expression of HIF-1 alpha. In the compression group at 21 and 28 days after surgery, Western blot analysis showed a significant increase in VEGF expression (P < 0.05). VEGF was localized to pericytes, Schwann cells, and macrophages. In the compression group at 21 days after surgery, neovascularization was observed, as indicated by an increase in the number of proliferating endothelial cells (which stained positive for BrdU).

CONCLUSION

Cauda equina compression seems to induce compensatory neovascularization of the cauda equina accompanied by an increase in VEGF expression.

The effects of a 5-HT2A receptor antagonist on blood flow in lumbar disc herniation: application of nucleus pulposus in a canine model

Blood vessel clots are found around the nerve root in patients with lumbar disc herniation. Thrombosis formation in the experimental application of nucleus pulposus to the nerve root has been shown in histological studies. In addition, reduction of blood flow and nerve conduction velocity are induced by the application of nucleus pulposus, which mimics lumbar disc herniation. In patients with lumbar disc herniation, nerve root block, which is thought to increase nerve blood flow, improves radiculopathy. 5-HT(2A) receptor antagonists are used in chronic arterial occlusive diseases to improve blood flow and have been reported to work as well as nonsteroidal anti-inflammatory drugs in improving radiculopathy due to lumbar disc herniation in clinical studies. This study investigated the effects of a 5-HT(2A) receptor antagonist on blood vessel diameter and blood flow in a canine experimental model of lumbar disc herniation. A total of 13 dogs were used. The animals were divided into three experimental groups and surgery was performed 1 week before measurements. In the nucleus pulposus group (NP; n = 5), the nucleus pulposus was applied to the nerve roots from the ventral side. In the sham group (n = 5), nucleus pulposus was not applied. In the naive group (n = 3), the animals did not undergo surgery. Measurements of vessel diameter and blood flow were done before and after administration of saline and drugs. The diameters and blood flow volume of the observed blood vessels were measured on video-recordings every 10 min for 65 min. In all groups, vessel diameter and blood flow did not change before or after administration of saline. In the NP and sham groups, vessel diameter and blood flow increased significantly after administration of 5-HTRA compared with the naive group. 5-HTRA improved blood vessel diameter and blood flow in the nerve roots inflamed by the application of nucleus pulposus but not in the intact nerve roots. 5-HTRA might be a potential agent to improve blood flow in the nerve roots of patients with lumbar disc herniation.

Industrial medicine and acute musculoskeletal rehabilitation. 5. Interventional procedures for work-related lumbar spine conditions

This chapter emphasizes the importance of establishing a differential diagnosis for low back pain (LBP) with and without referred lower-limb pain and outlines potential interventional treatments appropriate for each diagnosis. It is part of the study guide on industrial rehabilitation and acute musculoskeletal rehabilitation in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation. The article specifically focuses on the various interventions used to diagnose or treat those conditions commonly seen in patients with work-related LBP or referred pain in the lower limb. Current criterion treatments for lumbar disk pain, including surgical options, are reviewed.

OVERALL ARTICLE OBJECTIVE

To give an overview of the current state of diagnosis and treatment options for low back pain with or without referred leg pain focusing on interventional procedures.

Dermatomal laser-evoked potentials: a diagnostic approach to the dorsal root. Norm data in healthy volunteers and changes in patients with radiculopathy

We conducted a cross-sectional study of 40 radiculopathy patients in comparison with norm data from healthy subjects using a new electrophysiological method. Early manifestations of dorsal root impairment escape objective diagnosis by conventional somatosensory-evoked potentials due to the overlapping innervation of the affected dermatome by thickly myelinated mechanoreceptive afferents projecting to adjacent intact roots. Evidence suggested less intersegmental overlap for thermonociceptive afferents rendering laser-evoked potentials (LEP) sensitive to monosegmental dorsal root damage. Therefore we used this new method to study acute manifestations of monosegmental dorsal root pathology. Dorsal root function was tested in 12 healthy subjects and 40 sciatica patients by intraindividual interside comparison. Mechanosensibility and thermosensibility were clinically investigated. LEP were induced by moderately painful laser stimuli. The LEP were evaluated by amplitude and latency of the averaged electroencephalogram. Normal interside differences of LEP for amplitude were +/-22% (lower limb) and +/-35% (upper limb) and +/-15 to +/-16% for latency. Twenty-six patients (65%) showed significant LEP changes, mainly amplitude decreases. Six of these patients exhibited latency prolongations. Clinical testing yielded more frequent pathological results for pain compared to mechanosensibility. The study confirmed our preliminary evidence of LEP sensitivity to objectively document dorsal root impairment in patients suffering from acute monosegmental radiculopathy. This result opens the perspective of electrophysiologically differentiating the presence or absence of dorsal root pathology in patients with similar clinical symptoms but possibly different prognoses, which require different therapies.

Production of tumor necrosis factor-α from porcine nucleus pulposus cells at various time points in cell culture under conditions of nutritional deficiency

Nucleus pulposus (NP) in the epidural space induces spinal nerve damage not only by mechanical but also chemical mechanism. NP has been shown to be capable of producing tumor necrosis factor-alpha (TNF). TNF may play key roles in the NP-induced chemical damage. One of the main pathways to reach the avascular NP is diffusion from the blood supply of the vertebral body through the cartilage endplate. On disk herniation, when NP moves to the epidural space, the distance from the endplate to the herniated NP are longer in the herniated disk than in the intact disk. That is, it seems more difficult to receive adequate nutritional supply from the endplate in the sequestrated type. However, there have been only a few reports of the appearance of TNF in NP. The present study was performed to investigate TNF production in porcine NP under conditions of nutritional deficiency. NP cells were cultured and processed for immunohistochemistry using antisera to TNF, and for ELISA to measure TNF production. The latter was compared longitudinally. The immunoreactivity increased over time. On the other hand, the results of ELISA showed a peak in TNF production 12h, and lower amounts 1 day and 2 days after application of PBS. These observations may suggest that a nutritional deficit is a possible turn-on switch for TNF up-regulation in the NP.

Current concepts in the therapy of the spondyloarthritides

Recent success in the treatment of patients with the more severe forms of spondyloarthritides (SpA) has dramatically changed old paradigms. There is evidence that anti-tumor necrosis factor (TNF)-alpha therapy is highly effective in SpA, especially in ankylosing spondylitis (AS) and psoriatic arthritis. Based on recent data on more than 1000 patients with AS and psoriatic arthritis, this treatment seems to be even more effective than in rheumatoid arthritis (RA). The currently available anti-TNFalpha agents, infliximab, etanercept, and adalimumab, are approved for the treatment of RA in the US and in Europe. TNFalpha blockers may even be considered as a first-line treatment in patients with active AS whose condition is not sufficiently controlled with NSAIDs, as in the case of axial disease. There is preliminary evidence that both agents also work in other SpA, such as undifferentiated SpA. There is hope that ankylosis may be preventable, but it remains to be shown whether patients benefit from long-term anti-TNFalpha therapy and whether radiologic progression and ankylosis can be stopped. Furthermore, it seems that anti-TNFalpha therapy can also improve clinical manifestations of other inflammatory spinal disorders, such as sciatica and back pain caused by disc herniation, or possibly even intermittent inflammatory states of degenerative disc disease. Severe adverse events from treatment with anti-TNFalpha continue to be rare. Tuberculosis can be largely prevented by appropriate screening. As it stands now, the benefits of anti-TNFalpha therapy in AS seem to outweigh the shortcomings.

Pathophysiology of disk-related sciatica. I.--Evidence supporting a chemical component

Sciatica in patients with disk disease was long ascribed to pressure put on the sciatic nerve root by a herniated disk. However, a role for chemical factors acting in conjunction with this mechanical insult is suggested by a number of clinical observations: disk surgery does not consistently provide pain relief, large disk herniations are not always symptomatic, severe pain may be present in patients without imaging evidence of nerve root compression, the severity of symptoms and neurological signs is not well correlated with the size of the disk herniation, and conservative therapy is often effective. Experimental studies have provided further evidence for a chemical component: disk herniations can undergo spontaneous resorption, the intervertebral disk is immunogenic, and mediators for inflammation have been identified within intervertebral disk tissue. The current pathophysiological theory incriminates proinflammatory substances secreted by the nucleus pulposus (NP). When preexisting or concomitant mechanical injury to a nerve root occurs, these substances can cause nerve root pain. Animal experiments have established that the NP can induce functional and structural nerve root abnormalities in the absence of mechanical compression and that this effect is mediated by substances located at the surface of NP cells. Methylprednisolone, diclofenac, indomethacin, doxycycline, and cyclosporine induce variable inhibition of this effect. Available information points to tumor necrosis factor-alpha (TNF-alpha) as the main candidate among substances potentially responsible for nerve root pain. Therefore, trials of TNF-alpha antagonists in patients with disk-related sciatica are warranted.

Disc related cytokines inhibit axonal outgrowth from dorsal root ganglion cells in vitro

STUDY DESIGN

Application of nucleus pulposus and disc related cytokines in vitro on cultured dorsal root ganglion (DRG) cells.

OBJECTIVES

To study if tumor necrosis factor (TNF) and interleukin-1beta (IL-1beta) may induce similar inhibition of axonal outgrowth from cultured DRG cells as application of nucleus pulposus and to compare a new assessment method to previous data.

SUMMARY OF BACKGROUND DATA

Pro-inflammatory cytokines related to the intervertebral disc have been suggested to affect adversely neurons following local application, with implications for the nucleus pulposus-induced nerve injury seen in various studies. Nucleus pulposus is known to inhibit axonal outgrowth from cultured DRG cells, thereby indicating a neurotoxic potential. The mechanisms were not understood, but it was suspected that the effect was mediated by pro-inflammatory cytokines produced by the nucleus pulposus.

METHODS

DRG were harvested from newborn rats and put in culture. The axonal outgrowth was determined 24 hours after starting the culture. Twenty-four hours after exposing the cultured cells to nucleus pulposus, frozen nucleus pulposus, TNF, or IL-1beta, the axonal outgrowth was reassessed, and the outgrowth during the exposure time was calculated.

RESULTS

Nucleus pulposus clearly reduced the axonal outgrowth. Also, application of TNF and IL-1beta reduced the outgrowth but not as pronounced as the nucleus pulposus. Frozen nucleus pulposus had no effects on the outgrowth. Overall, the data were similar regarding frozen and nonfrozen nucleus pulposus compared to a previous study.

CONCLUSIONS

It was evident that the 2 studied cytokines inhibited the outgrowth of axons from cultured DRG cells, thus suggesting a neurotoxic potential. However, the inhibition was not as pronounced as for nucleus pulposus. These data may increase our understanding for cytokine induced nerve injury, with implications for future treatment strategies for such conditions.

Effect of acute nerve root compression on endoneurial fluid pressure and blood flow in rat dorsal root ganglia

The objective of the current study was to test the hypothesis that crush injury to nerve root increases endoneurial fluid pressure (EFP) and decreases blood flow in the associated dorsal root ganglion (DRG). A total of 21 adult, female Sprague-Dawley rats had their left L5 nerve root and DRG exposed. The L5 nerve root was clamped for 2 s with a vascular suture clip just proximal to the DRG (compression group). Sham-operated animals without compression were used for control (control group). EFP was recorded with a servo-null micropipette system using a glass micropipette with tip diameter of 4 mum before and after 3 h of treatment. After the final measurement of EFP, DRG was excised and processed for histology. Blood flow in the DRG was continuously monitored by laser Doppler flow meter for 3 h. Three hours after treatment, EFP was 4.7+/-2.7 cm H(2)O in the compression group and 2.2+/-1.2 cm H(2)O in the control group (P<0.05). Edema was the principal pathologic findings seen consistently in the DRG from animals in the compression group. Blood flow in the compression group was reduced 10 min after compression. This reduction was statistically significant compared with that of the control (P<0.01). An acute compression to the nerve root increased endoneurial edema, increased EFP in the associated DRG, and reduced DRG blood flow. This combination of increased EFP and decreased blood flow in the DRG may result in neuronal ischemia and sensory dysfunction. These acute pathophysiologic changes may thus have a role in the pathogenesis of low back pain and sciatica due to disc herniation and spinal canal stenosis.

Indomethacin blocks the nucleus pulposus-induced effects on nerve root function. An experimental study in dogs with assessment of nerve conduction and blood flow following experimental disc herniation

Inflammatory mechanisms have been suggested to be involved in the basic pathophysiologic events leading to nerve root injury after local application of nucleus pulposus. To assess if these nucleus pulposus-induced effects could be blocked by anti-inflammatory treatment, 41 dogs were exposed to either incision of the L6-7 disc to induce experimental disc herniation with (n=12) or without (n=14) indomethacin treatment per os (5 mg/kg per day), and no incision with (n=5) or without (n=10) indomethacin. Intraneural blood flow and nerve conduction velocity were assessed after 7 days to evaluate the degree of nerve injury. Disc incision induced a reduction in nerve root and dorsal ganglion blood flow as well as nerve function, similarly to previous studies. However, simultaneous treatment with indomethacin efficiently blocked the negative effects on both blood flow and nerve conduction but had no effects per se. The present study thus indicates that inflammatory mechanisms may be of relevance in the pathophysiology of nucleus pulposus-induced nerve root injury and thereby also for sciatica.

Effects of nucleus pulposus on nerve root neural activity, mechanosensitivity, axonal morphology, and sodium channel expression

STUDY DESIGN

This study analyzed the effects of autografted nucleus pulposus on nerve root axon morphology, neurophysiologic function, and sodium channel expression.

OBJECTIVES

To investigate the chronic effects of the epidural implantation of nucleus pulposus on nerve root morphology, neural activity, ectopic discharge, mechanosensitivity, and sodium channel expression.

SUMMARY OF BACKGROUND DATA

It has been reported that ectopic discharges were recorded antidromically from sural nerve on compressing nucleus pulposus exposed spinal nerves. However, it is not clear what the effects of nucleus pulposus are on ectopic discharges recorded directly from the spinal nerve roots. It is also not clear what the effects of nucleus pulposus are on the threshold pressure to provoke ectopic discharges in the spinal nerves. Sodium channel content increases in remodeling axons after nerve injury, but it is not clear what the effects of nucleus pulposus are on sodium channel expression in spinal nerve.

METHODS

Forty-six male Sprague-Dawley rats were used, 20 in a nucleus pulposus-implanted group, 18 in a fat-implanted group, and 8 in a normal group. Fresh autografted nucleus pulposus or fat tissue was implanted into the dorsal epidural space at the L4-L5 disc level. On the 7th, 21st, or 42nd day, neurophysiologic recordings were made to determine nerve root response to compression. Nerve roots were then harvested to determine sodium channel protein concentration and histologic changes in the nerve root. The correlations between sodium channel density and neural activity and mechanosensitivity of dorsal root were analyzed statistically.

RESULTS

Ectopic discharge rate was higher in nucleus pulposus 7-day group. Threshold pressure to evoke ectopic discharges was lower in the nucleus pulposus 7-day group, and higher in the nucleus pulposus 42-day group compared to the normal group. Sodium channel protein density increased in the nucleus pulposus 7-day and nucleus pulposus 21-day group compared to normal nerve. Sodium channel density changes were not correlated to threshold pressure. Ectopic discharge rate increased with increase of sodium channel density in the nerve roots. The number of axons with neuropathy increased in the nucleus pulposus 7-day and 21-day groups.

CONCLUSIONS

Acute exposure of nerve root to nucleus pulposus resulted in increased number of axons with neuropathy, higher intensity of ectopic discharges on compression, and nerve mechanosensitization. Chronic exposure resulted in mechanical desensitization. Changes of sodium channel density were correlated to ectopic discharge rate.

Pathomechanisms of nerve root injury caused by disc herniation: an experimental study of mechanical compression and chemical irritation

STUDY DESIGN

An electrophysiologic and histologic study on nerve roots after mechanical compression and/or local application of nucleus pulposus (NP) was performed.

OBJECTIVE

To assess the effects of mechanical compression and/or chemical irritation caused by NP.

SUMMARY OF BACKGROUND DATA

It has been shown that application of NP to nerve roots without compression induces histologic and functional changes in nerve roots and the dorsal root ganglia. In clinical situations, however, mechanical compression has also been considered an important factor in disc herniation.

METHODS

Eighteen dogs (9-15 kg) were used in this study. Four groups were used to assess the effect of each factor: 1) sham group (n = 3); 2) NP group (NP applied under the S1 lamina) (n = 5); 3) comp group (a plastic balloon placed under the S1 lamina) (n = 5); and 4) comp+NP group (a balloon and NP placed under the S1 lamina) (n = 5). Ascending cauda equina action potentials (CEAPs) and cauda equina-sensory nerve conduction velocity (SCV) were recorded before, immediately after, and 1 week after treatment. Histologic changes were also assessed by light microscopy.

RESULTS

There were no significant differences in CEAP and SCV among the four groups immediately after the treatment. However, 1 week after treatment, the amplitudes in the NP group, comp group, and comp+NP group were statistically significantly lower compared with those in the sham group. The comp+NP group showed significantly lower amplitude than did the NP group and comp group. Immediately after treatment, SCV in the NP group and comp group did not show significant differences compared with that in the sham group. However, 1 week after treatment, SCV in the comp+NP group was significantly lower compared with that in the sham group. Histologic changes such as intraneural edema, Schwann cell edema, and nerve fiber injury seemed to be more pronounced in the comp+NP group than in the other groups.

CONCLUSIONS

It was shown that each of the assessed factors induces nerve dysfunction. However, the combination of mechanical compression (mass effect of herniated NP) and chemical irritation (inflammation around nerve root) may induce more nerve root injury than each factor per se.

Selective nerve root blocks for the treatment of sciatica: evaluation of injection site and effectiveness--a study with patients and cadavers

PURPOSE

To relate different types of radiographic contrast material distributions to anatomic compartments by using cadaveric specimens and to relate the injection site to treatment-induced discomfort and therapeutic effect.

MATERIALS AND METHODS

The contrast material distributions of selective nerve root blocks (SNRBs) in 36 patients (13 women, 23 men; mean age, 52 years; age range, 22-88 years) were graded by two radiologists in conference as type 1 (tubular appearance), type 2 (nerve root visible as filling defect), or type 3 (nerve root not visible). These patterns were correlated with pain reduction after 15 minutes and 2 weeks (with a visual analogue scale of 100-mm length). In addition, 30 nerve roots were injected with iodine-containing contrast material and blue dye in three cadaveric specimens. Radiographs were compared with anatomic sections.

RESULTS

After 15 minutes and 2 weeks, 75% and 86% of the patients, respectively, reported pain relief. Mean pain relief length after 15 minutes for type 1 distribution was 60 mm; for type 2, 44 mm; and for type 3, 22 mm; and after 2 weeks, it was 34 mm for type 1, 31 mm for type 2, and 57 mm for type 3. There was no correlation between early and late response. Pain during intervention was less pronounced in type 2 injection, compared with type 1 (P = .002). On the basis of anatomic sections, type 1 injection was intraepineural; type 2, extraepineural; and type 3, paraneural.

CONCLUSION

Therapeutic SNRB is effective in sciatica, but early response does not predict the effect after 2 weeks. Type 1 injections are more painful than type 2 injections.

Blood flow measurement in experimental chronic cauda equina compression in dogs: changes in blood flow at various conditions

The purpose of this study was to present a simple method of measurement of blood flow in the nerve root, assess the reliability of this method, and examine the changes of blood flow in chronic cauda equina compression in an experimental setting. A total of 15 dogs were used to determine the blood flow of cauda equina in normal (n = 5), sham (n = 5), and 10 mm Hg compressed cauda equina for 1 week (n = 5). The speed of blood flow was calculated using a specially designed microscope supplied with a video camera. Blood flow in chronic 10 mm Hg compression decreased compared with the sham and normal groups. The kappa value was between 0.75 and 0.96. We conclude that this method might be useful for measurement of blood flow in the nerve root and for confirming the reduction in blood flow of compressed cauda equina.

Selective inhibition of tumor necrosis factor-alpha prevents nucleus pulposus-induced thrombus formation, intraneural edema, and reduction of nerve conduction velocity: possible implications for future pharmacologic treatment strategies of sciatica

STUDY DESIGN

The possibility to prevent nucleus pulposus-induced functional and structural nerve root injury by selective tumor necrosis factor-alpha inhibition was assessed in an experimental model in the pig spine.

OBJECTIVE

The objective of the study was to evaluate the role of tumor necrosis factor-alpha in the mediation of nucleus pulposus-induced nerve injury by using selective inhibition.

SUMMARY OF BACKGROUND DATA

The cytokine tumor necrosis factor-alpha has been suggested to play a key role in the nerve root injury induced by local application of nucleus pulposus. However, previous studies have not been able to distinguish the effects between tumor necrosis factor-alpha and other disc-related cytokines because of the use of nonspecific cytokine inhibition.

METHODS

Autologous nucleus pulposus was harvested from a lumbar disc and applied to the porcine sacrococcygeal cauda equina. The pigs were simultaneously treated with two selective tumor necrosis factor-alpha inhibitors (etanercept n = 8 and infliximab n = 5), a heparin analogue (enoxaparin n = 5) or saline for control (n = 5). After 7 days the nerve conduction velocity over the application zone was determined and samples of the exposed nerve roots were collected for light microscopic evaluation.

RESULTS

The two tumor necrosis factor-alpha inhibitors prevented the reduction of nerve conduction velocity and also seemed to limit the nerve fiber injury, the intracapillary thrombus formation, and the intraneural edema formation. However, treatment with enoxaparin did not seem to be different from control regarding reduction of nerve conduction velocity or histologic changes.

CONCLUSIONS

The data clearly indicate that tumor necrosis factor-alpha is involved in the basic pathophysiologic events leading to nerve root structural and functional changes after local application of nucleus pulposus. The study therefore provides a basic scientific platform with potential clinical implications regarding the use of anti-tumor necrosis factor-alpha medication as treatment in patients with disc herniation and sciatica.

Application of nucleus pulposus to the nerve root simultaneously reduces blood flow in dorsal root ganglion and corresponding hindpaw in the rat

STUDY DESIGN

An experimental study to clarify the effects of nucleus pulposus on blood flow in the dorsal root ganglion and hindpaws.

OBJECTIVES

To investigate the effects of application of nucleus pulposus to nerve root on blood flow in the dorsal root ganglion and the corresponding hindpaw.

SUMMARY OF BACKGROUND DATA

It has been reported experimentally that application of nucleus pulposus into the epidural space induces morphologic and functional changes in the nerve roots and induces compartment syndrome in the dorsal root ganglia. However, it has not been clarified which of these changes induces symptoms in the lower limbs.

METHODS

Sixteen adult, female Sprague-Dawley rats had the left L5 nerve root and associated dorsal root ganglions exposed. Autologous nucleus pulposus was applied to the L5 nerve root, just proximal to the dorsal root ganglion (NP group). For control, the same volume of muscle tissue was applied similarly to the neural tissue (control group). Blood flow in the dorsal root ganglion, corresponding hindpaw, and the contralateral hindpaw was continuously monitored by two-channel laser Doppler flowmeter for 3 hours. After measurement of blood flow, the nerve root and dorsal root ganglion were processed for histology and evaluated by light microscope.

RESULTS

Blood flow in the NP group was reduced, not only in the dorsal root ganglion, but also in the corresponding hindpaw. These reductions were statistically significant compared with the control group (P < 0.01). Edema was the principal pathologic finding seen consistently in the nerve roots and in many of the associated dorsal root ganglia from nucleus pulposus-treated animals.

CONCLUSION

Application of nucleus pulposus to nerve root decreased blood flow in the dorsal root ganglion and corresponding hindpaw. These basic pathophysiologic changes are associated with compression injuries caused by herniated discs and are accepted neuropathologic mechanisms of injury associated with painful neuropathies. These acute observations in the dorsal root ganglion and the hindpaw may be important initial factors in the pathogenesis of radicular leg pain (sciatica) due to disc herniation.