Elsevier

Surgical Neurology

Volume 72, Issue 5, November 2009, Pages 496-500
Surgical Neurology

Pain
Ultrastructural evaluation of pulsed radiofrequency and conventional radiofrequency lesions in rat sciatic nerve

https://doi.org/10.1016/j.surneu.2008.11.016Get rights and content

Abstract

Background

PRF treatment has recently been described as minimally neurodestructive alternative to radiofrequency heat lesions. Patients with some pain syndromes in whom the pain could not be controlled by alternative techniques may be treated using PRF. In the present study, our main goal was to evaluate and compare the ultrastructure of peripheral nerve tissue that was heated by PRF, CRF with 42°C, and CRF with 70°C.

Methods

Forty-five male rats were divided into 5 groups. In PRF group and CRF with 42°C group, the sciatic nerve was heated at a temperature of 42°C for 120 seconds. As a positive control, some rat sciatic nerves were treated with CRF lesions at 70°C. The rats were kept alive for 21 days and then killed. Tissue was evaluated with transmission electron microscope, and grading was done to the groups.

Results

The unmyelinated nerve fibers were ultrastructurally normal in all groups. The results of myelinated axons indicated that PRF group had better grades, and CRF with 70°C group had the worst grade. Especially, comparison of the group of PRF and CRF with 42°C revealed significant difference. In PRF group, none of the myelinated axons showed severe degeneration findings, and most of the damaged myelinated axons showed only separation in myelin configuration.

Conclusions

PRF treatment may cause separation in myelinated axons. However, it seems that all changes were reversible. The present study supports the hypothesis that pulsed RF treatment does not rely on thermal injury of neurologic tissue to achieve its effect.

Introduction

RF treatments have been used for more than 30 years for a variety of pain syndromes as follows: occipital neuralgia [7], cervical radicular pain [18], [25], intercostal neuralgia [26], lumbar radicular pain [10], mechanical low back pain because of the zygapophyseal joints dysfunction [6], and discogenic pain [8]. In addition, the CRF is used for computed tomography-guided percutaneous cordotomy, extralemniscal myelotomy, and trigeminal tractotomy [12]. In the application of CRF, heat is produced in the tissues surrounding the RF electrode tip [21]. The result is a coagulative necrosis of the targeted tissue that is not conceptually different from other neurolytic procedures designed to destruct sensory pathways for pain relief [16].

The PRF is a newly defined energy type, in which a relatively high voltage is applied intermittently to the neural tissue. Sluijter et al [20] proposed that the effect of PRF is due to the EMF produced during the application. PRF has recently been introduced as an alternative method of pain intervention and is rapidly gaining acceptance because it is an apparently effective therapy that does not cause extensive tissue injury. It has been suggested that PRF might be suitable for use in patients with neuropathic pain in whom the pain could not be controlled by invasive techniques and oral medication [20]. However, the mechanism of therapeutic effect PRF is still controversial.

The purpose of this study was to investigate the effects of PRF on neuronal histopathologic condition and ultrastructure in rat sciatic nerve and to compare with the effects of CRF and low-temperature CRF.

Section snippets

Surgical procedure

Twenty-five male Wistar rats, weighing between 180 and 220 g were used. The rats were anesthetized with ketamine hydrochloride, 100 mg/kg (Ketalar, Eczacıbası, Istanbul, Turkey), and xylazine, 5 mg/kg (Rompun; Bayer, Leverkusen, Germany). All surgical procedures were performed by the same surgeon with the aid of an operating microscope. The right sciatic nerve was used for the surgical procedures. An ECG pad was used as a return electrode for the RF generator and placed on the rat's chest. A

Results

During the experiment, all rats were alive. None of them developed wound infections and autotomy. In the transmission electron microscopic examination of the unmyelinated axons, they were found to be normal ultrastructurally, in all of the groups (Fig. 2, Fig. 3).

In group 1 (control group), nearly all of the myelinated axons were found to be normal, ultrastructurally (Fig. 1).

In group 2 (sham group), most of the myelinated axons were found to be normal; however, in a few of the myelinated

Discussion

PRF has recently been introduced as a nonneurodestructive or minimally neurodestructive alternative to radiofrequency for the management of chronic pain [2], [20]. In particular, recent manuscripts by Van Zundert et al [28], [29] report no side effects in a series of patients treated with percutaneous PRF for chronic cervical and trigeminal pain syndromes. An editorial reviewing the current literature concludes that PRF stimulation of the DRGs is a valid neuromodulation technique that is not

Conclusion

This is the first experimental study showing the ultrastructural effects of PRF on peripheral nerve tissue quantitatively. Ultrastructural analysis was showed significant differences between the PRF and CRF groups. We think that separation in myelin configuration may result in blockage or interruption of the nerve signal through that nerve pathway that may be responsible for reversible neuronal depression. PRF may be used as a test method to decide to make permanent RF lesions if it works.

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