Ectopic firing due to artificial venous stasis in rat lumbar spinal canal stenosis model: a possible pathogenesis of neurogenic intermittent claudication

Development of a Machine Learning Algorithm to Correlate Lumbar Disc Height on X-rays with Disc Bulging or Herniation

Lumbar disc bulging or herniation (LDBH) is one of the major causes of spinal stenosis and related nerve compression, and its severity is the major determinant for spine surgery. MRI of the spine is the most important diagnostic tool for evaluating the need for surgical intervention in patients with LDBH. However, MRI utilization is limited by its low accessibility. Spinal X-rays can rapidly provide information on the bony structure of the patient. Our study aimed to identify the factors associated with LDBH, including disc height, and establish a clinical diagnostic tool to support its diagnosis based on lumbar X-ray findings. In this study, a total of 458 patients were used for analysis and 13 clinical and imaging variables were collected. Five machine-learning (ML) methods, including LASSO regression, MARS, decision tree, random forest, and extreme gradient boosting, were applied and integrated to identify important variables for predicting LDBH from lumbar spine X-rays. The results showed L4-5 posterior disc height, age, and L1-2 anterior disc height to be the top predictors, and a decision tree algorithm was constructed to support clinical decision-making. Our study highlights the potential of ML-based decision tools for surgeons and emphasizes the importance of L1-2 disc height in relation to LDBH. Future research will expand on these findings to develop a more comprehensive decision-supporting model.

Venous congestion as a central mechanism of radiculopathies

Compression of roots/nerves can disrupt some of their functions, but does not necessarily cause pain. This is illustrated by the frequency of nearly asymptomatic spinal stenosis or disc herniations. In fact, pain of radiculopathies (and nerve entrapments) may mostly be the consequence of intraneural oedema induced by microscopical venous stasis around roots/spinal ganglia (or nerves) not or poorly shown by imaging. This narrative review first lists arguments for a role of congestion of vasa-nervorum in the pathophysiology of radiculopathies, including those induced by disc herniation and spinal stenosis, but also other sources of overpressures in spinal venous plexuses (pregnancy, vena cava atresia and thrombosis, portal hypertension, epidural varices, arterio-venous fistula, vertebral hemangioma or hemangioblastoma). It also details sources of venous congestion around nerves outside the spine, from pelvis (May-Thurner syndrome, Nut-cracker syndrome) to buttocks (superior and inferior gluteal veins), and even thighs and legs. A better recognition of a preeminent role of venous congestion in radiculopathies, plexopathies, and nerve entrapments, should have major consequences: (i) discard the dogma that compression is mandatory to induce root/nerve suffering, since root/nerve adherences in two locations can impair blood flow in vasa-nervorum through root/nerve stretching; (ii) implementation of sensitive techniques to visualise impingement of blood flow around or within roots and nerves; (iii) better prevention of roots/nerves adherence, or arachnoiditis induced by extravascular fibrin deposition secondary to venous stasis.; (iv) optimizing treatments dampening clot formation and/or extravascular fibrin leakage in the intradural/peridural spaces, or around roots/nerves, like guided injection of tissue plasminogen activator.

Effect of epidural polydeoxyribonucleotide in a rat model of lumbar foraminal stenosis

Background

We aimed to investigate the effect of epidural polydeoxyribonucleotide (PDRN) on mechanical allodynia and motor dysfunction in a rat model of lumbar foraminal stenosis (LFS).

Methods

This study was conducted in two stages, using male Sprague-Dawley rats. The rats were randomly divided into eight groups. In the first stage, the groups were as follows vehicle (V), sham (S), and epidural PDRN at 5 (P5), 8 (P8), and 10 (P10) mg/kg; and in the second stage, they were as follows intraperitoneal PDRN 8 mg/kg, epidural 3,7-dimethyl-1-propargilxanthine (DMPX) (0.1 mg/kg), and DMPX (0.1 mg/kg). The LFS model was established, except for the S group. After an epidural injection of the test solutions, von Frey and treadmill tests were conducted for 3 weeks. Subsequently, histopathologic examinations were conducted in the V, S, P5, and P10 groups.

Results

A total of 65 rats were included. The P8 and P10 groups showed significant recovery from mechanical allodynia and motor dysfunction at all time points after drug administration compared to the V group. These effects were abolished by concomitant administration of DMPX. On histopathological examination, no epineurial inflammation or fibrosis was observed in the epidural PDRN groups.

Conclusions

Epidural injection of PDRN significantly improves mechanical allodynia and motor dysfunction in a rat model of LFS, which is mediated by the spinal adenosine A_2A receptor. The present data support the need for further research to determine the role of epidural PDRN in spinal stenosis treatment.

Unilateral repetitive tibial nerve stimulation improves neurogenic claudication and bilateral F-wave conduction in central lumbar spinal stenosis

BACKGROUND

Repetitive electrical nerve stimulation of the lower limb may improve neurogenic claudication in patients with lumbar spinal stenosis (LSS) as originally described by Tamaki et al. We tested if this neuromodulation technique affects the F-wave conduction on both sides to explore the underlying physiologic mechanisms.

METHODS

We studied a total of 26 LSS patients, assigning 16 to a study group receiving repetitive tibial nerve stimulation at the ankle (RTNS) on one leg, and 10 to a group without RTNS. RTNS conditioning consisted of a 0.3-ms duration square-wave pulse with an intensity 20% above the motor threshold, delivered at a rate of 5 Hz for 5 min. All patients underwent the walking test and the F-wave and M-wave studies for the tibial nerve on both sides twice; once as the baseline, and once after either the 5-min RTNS or 5-min rest.

RESULTS

Compared to the baselines, a 5-min RTNS increased claudication distance (176 ± 96 m vs 329 ± 133 m; p = 0.0004) and slightly but significantly shortened F-wave minimal onset latency (i.e., increased F-wave conduction velocity) not only on the side receiving RTNS (50.7 ± 4.0 ms vs 49.2 ± 4.2 ms; p = 0.00081) but also on the contralateral side (50.1 ± 4.6 ms vs 47.9 ± 4.2 ms; p = 0.011). A 5-min rest in the group not receiving RTNS neither had a significant change on claudication distance nor on any F-wave measurements. The M response remained unchanged in both groups.

CONCLUSIONS

The present study verified a beneficial effect of unilaterally applied RTNS of a mild intensity on neurogenic claudication and bilateral F-wave conduction. Our F-wave data suggest that this type of neuromodulation could be best explained by an RTNS-induced widespread sympathetic tone reduction with vasodilation, which partially counters a walking-induced further decline in nerve blood flow in LSS patients who already have ischemic cauda equina.

Mechanical properties of nerve roots and rami radiculares isolated from fresh pig spinal cords

No reports have described experiments designed to determine the strength characteristics of spinal nerve roots and rami radiculares for the purpose of explaining the complexity of symptoms of medullary cone lesions and cauda equina syndrome. In this study, to explain the pathogenesis of cauda equina syndrome, monoaxial tensile tests were performed to determine the strength characteristics of spinal nerve roots and rami radiculares, and analysis was conducted to evaluate the stress-strain relationship and strength characteristics. Using the same tensile test device, the nerve root and ramus radiculares isolated from the spinal cords of pigs were subjected to the tensile test and stress relaxation test at load strain rates of 0.1, 1, 10, and 100 s^-1 under identical settings. The tensile strength of the nerve root was not rate dependent, while the ramus radiculares tensile strength tended to decrease as the strain rate increased. These findings provide important insights into cauda equina symptoms, radiculopathy, and clinical symptoms of the medullary cone.

Circulatory dynamics of the cauda equina in lumbar canal stenosis using dynamic contrast-enhanced magnetic resonance imaging

BACKGROUND CONTEXT

There has been no study regarding the cauda equina circulation of patients with neurogenic intermittent claudication (NIC) in lumbar spinal canal stenosis (LSCS) using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

PURPOSE

The mechanism responsible for the onset of NIC was investigated using DCE-MRI to examine changes in cauda equina blood flow in patients with LSCS.

STUDY DESIGN

This was a retrospective longitudinal registry and magnetic resonance imaging study.

PATIENT SAMPLE

The subjects consisted of 23 patients who had LSCS associated with NIC (stenosis group). Ten asymptomatic volunteers who did not have NIC served as controls (control group). In the LSCS group, the cross-sectional area of the dural sac was <75 mm2 at the site of most severe stenosis. These patients were further divided into single and double stenosis subgroups.

OUTCOME MEASURES

The main measures we used were the signal intensity (S-I) ratio and the shape and size of the time intensity (T-I) curves. We compared these between the stenosis and control groups.

METHODS

At first, plain T1-weighted MR images were obtained and the lumbar dural sac cross-sectional area was measured using a digitizer. For DCE-MRI, sagittal T1-weighted images of the same slice were acquired continuously for 10 minutes after administration of gadolinium as an intravenous bolus to observe the distribution of contrast medium (gadolinium) in the cauda equina. To objectively evaluate changes in contrast enhancement of the cauda equina at the site of canal stenosis, regions of interest were established. The signal intensity (SI) ratio was calculated to compare the signal intensities before and after contrast enhancement, and time-intensity curves were prepared to investigate changes over time.

RESULTS

The static imaging findings and the changes of gadolinium uptake showed striking differences between the study and control patients. In the stenosis group, abnormal intrathecal enhancement showed around the site of stenosis on enhanced MR imaging. The SI ratio at the site of canal stenosis had a slower increase in the arterial phase when compared with that in the control group and remained high in the venous phase for up to 10 minutes. Finally, abnormal intrathecal enhancement was visible around the site of stenosis on enhanced MR imaging in all patients.

CONCLUSIONS

These clinical data indicate that cauda equina nerve roots in the LSCS patients are pathologic even when symptoms are not elicited in the supine position, suggesting that intraradicular venous congestion and edema themselves do not influence the existence of radicular symptoms.

Pathophysiology, diagnosis and treatment of intermittent claudication in patients with lumbar canal stenosis

Spinal nerve roots have a peculiar structure, different from the arrangements in the peripheral nerve. The nerve roots are devoid of lymphatic vessels but are immersed in the cerebrospinal fluid (CSF) within the subarachnoid space. The blood supply of nerve roots depends on the blood flow from both peripheral direction (ascending) and the spinal cord direction (descending). There is no hypovascular region in the nerve root, although there exists a so-called water-shed of the bloodstream in the radicular artery itself. Increased mechanical compression promotes the disturbance of CSF flow, circulatory disturbance starting from the venous congestion and intraradicular edema formation resulting from the breakdown of the blood-nerve barrier. Although this edema may diffuse into CSF when the subarachnoid space is preserved, the endoneurial fluid pressure may increase when the area is closed by increased compression. On the other hand, the nerve root tissue has already degenerated under the compression and the numerous macrophages releasing various chemical mediators, aggravating radicular symptoms that appear in the area of Wallerian degeneration. Prostaglandin E1 (PGE1) is a potent vasodilator as well as an inhibitor of platelet aggregation and has therefore attracted interest as a therapeutic drug for lumbar canal stenosis. However, investigations in the clinical setting have shown that PGE1 is effective in some patients but not in others, although the reason for this is unclear.

Neurogenic claudication without spinal stenosis arising as a result of lumbar epidural varices

Neurogenic claudication is most frequently observed in patients with degenerative lumbar spinal stenosis. We describe a patient with lumbar epidural varices secondary to obstruction of the inferior vena cava by pathological lymph nodes presenting with this syndrome. Following a diagnosis of follicular lymphoma, successful chemotherapy led to the resolution of the varices and the symptoms of neurogenic claudication.

The lumbar epidural venous plexus may have an important role in the pathogenesis of spinal stenosis. Although rare, epidural venous engorgement can induce neurogenic claudication without spinal stenosis. Further investigations should be directed at identifying an underlying cause.

Changes in blood flow, oxygen tension, action potentials, and vascular permeability induced by arterial ischemia or venous congestion on the lumbar dorsal root ganglia in dogs

It is generally believed that radiculopathy associated with the degenerative conditions of the spine may result from both mechanical compression and circulatory disturbance. However, the basic pathophysiology of circulatory disturbance induced by ischemia and congestion is not fully understood. This study investigated the effect of ischemia and congestion on the dorsal root ganglion (DRG) using an in vivo model. The sixth and seventh lumbar laminae were removed and the seventh lumbar DRG was exposed using adult dogs. The aorta was clamped as an ischemic model in the DRG, and the inferior vena cava was clamped as a congestion model at the sixth costal level for 30 min using forceps transpleurally. Measurements of blood flow, partial oxygen pressure, and action potentials in the DRG were recorded over a period of 1 h after clamp release. Finally, we examined the status of intraganglionic blood permeability under a fluorescence microscope following injection of Evans blue albumin into the cephalic vein to determine the type of circulatory disturbance occurring in the DRG. Immediately after inferior vena cava clamping, the central venous pressure increased approximately four times and marked extravasation of protein tracers was induced in the lumbar DRG. Blood flow, partial oxygen pressures, and action potentials within the DRG were more severely affected by the aorta clamping; however, this ischemic model did not reveal any permeability changes in the DRG. The permeability change in the DRG was more easily increased via venous congestion than by arterial ischemia. The intraganglionic venous flow was stopped with compression at much lower pressures than that needed to impact arterial flow. From a clinical perspective, intraganglionic edema formation, rather than arterial ischemia, may be an earlier phenomenon inducing DRG dysfunction.

Effects of arterial ischemia and venous congestion on the lumbar nerve root in dogs

The development of radiculopathy in patients with lumbar canal stenosis is thought to be closely related to intraradicular edema resulting from compression. However, there is little agreement as to question which is more essential for intermittent claudication: ischemia or congestion. The aim of the present experimental investigation was to examine the effect of ischemia and congestion on the nerve root using dogs. The aorta was clamped as an ischemia model of the nerve root and the inferior vena cava was clamped as a congestion model at the sixth costal level for 30 min using forceps transpleurally. Measurements of blood flow, partial oxygen pressure, and conduction velocity in the nerve root were repeated over a period of 1 h after release of clamping. Finally, we examined the status of intraradicular blood-nerve barrier under fluorescence and transmission electron microscope. Immediately after clamping of the inferior vena cava, the central venous pressure increased by about four times and marked extravasation of protein tracers was induced in the lumbar nerve root. Blood flow, partial oxygen pressure, and conduction velocity of the nerve root were more severely affected by aorta clamp, but this ischemia model did not show any intraradicular edema. The blood-nerve barrier in the nerve root was more easily broken by venous congestion than by arterial ishemia. In conclusion, venous congestion may be an essential factor precipitating circulatory disturbance in compressed nerve roots and inducing neurogenic intermittent claudication.