|RESPONSE TO LETTER TO THE EDITOR
|Year : 2016 | Volume
| Issue : 3 | Page : 211-212
Mechanism of pulsed and continuous radiofrequency ablation
Pain Clinic of India Pvt., Ltd., Fortis Hospital and Global Hospitals, Mumbai, Maharashtra, India
|Date of Web Publication||10-Jan-2017|
2005/A, Cosmic Heights, Bhakti Park, Wadala East, Mumbai - 400 037, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Kothari K. Mechanism of pulsed and continuous radiofrequency ablation. Indian J Pain 2016;30:211-2
I thank you for writing a letter. Your letter points toward one of the very important questions - what is the mechanism of action of radiofrequency (RF). Is it heat only or it has something to do with electromagnetic fields created around the needle tip. We need to find the answer to the question - is there any other mechanism by which RF is showing its effect.
The queries you raised are thought provoking. I agree that by going for the theory of heat lesion, we cannot explain the effect of RF in the superior hypogastric nerve block. Anatomicaly we know that the superior hypogastric plexus is large plexus and application of RF at single point does not explain how it can block the pain impulses travelling through this large plexus and in turn relieve the pain arising out of pelvic viscera due to various causes including malignancy.
In the late 80's, there were questions raised about validation of the theory of heat as a prime mechanism of RF effect.  There were findings in some experiments that RF applied away from the target nociceptive site could also be effective and pulsed RF (pRF) was invented. Since then, many researchers have found that continuous RF (CRF) and pRF may have more mechanisms then only heat.
In 2005, six cases were treated with intra-articular pRF and pain relief was noted.  These findings gave a new dimension to the researchers.
If PRF has a local anti-inflammatory effect, it might possibly also have a general effect on the immune system if the mode of application could be adapted. The scope of this new method may have large dimensions because the immune system is involved in so many pathological conditions. This goes beyond well-known conditions like the autoimmune diseases. For example, stress and allostatic load are connected to a whole list of serious diseases such as cancer and cardiovascular disease (Sluijter and Imani).
We know now that the RF signal on an electrode produces two types of basic fields in the tissue : 0 electrical fields and magnetic fields. At 500 kHz, magnetic fields are negligible. It is the electric field (E) that is the origin of all effects we see in RF lesioning, in both CRF lesioning (CRFL) and pRF lesioning (PRFL). The E-field produces forces on ions and other charged structures. This produces movement of ions in electrolytes, current densities j, and stresses on cellular substructures and membranes. Currents j, in turn, produces ionic friction and heat, and this then produces the increase in temperature seen in CRFL and PRFL. All of these mechanisms, not just temperature rise, have the potential of producing modifications of neural structures and neuronal behavior when the E-field becomes high enough. All of these mechanisms might be relevant to understanding how RF lesioning produces its effects in pain relief therapy. , The fact that application of pRF in the joint space (Intra-articular) can produce pain relief suggests that the mechanism of pain relief in pRF may be its influence on the immune system.
There were other theories like increased c-fos expression in the dorsal horn. In the fields of molecular biology and genetics, c-fos is a proto-oncogene that is the human homolog of the retroviral oncogene v-fos. It was first discovered in rat fibroblasts as the transforming gene of the Finkel-Biskis-Jinkins murine osteogenic sarcoma virus. Another hypothesis was the long-term depression of the higher afferent synapses which could not be proven till today.
As pointed out by you in your letter, the role of CRF is questionable for the pain relief in these set of patients (superior hypogastric nerve block), but we must keep in mind about probable role of electromagnetic field effects even in CRF treatment groups. Hence, before we label them as placebo effect, we must think in that trajectory.
I conclude with the remark that newer insights are being provided by research on pRF and CRF, and by going with the present evidence, it is better to apply pRF rather than CRF for superior hypogastric nerve block for treating patients.
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Conflicts of interest
There are no conflicts of interest.
| References|| |
Sluijter ME, Imani F. Evolution and mode of action of pulsed radiofrequency. Anesth Pain 2013;2:139-41.
Sluijter ME, Teixeira A, Serra V, Balogh S, Schianchi P. Intra-articular application of pulsed radiofrequency for arthrogenic pain - r0 eport of six cases. Pain Pract 2008;8:57-61.
Cosman ER Jr., Cosman ER Sr. Electric and thermal field effects in tissue around radiofrequency electrodes. Pain Med 2005;6:405-24.
Simopoulos TT, Kraemer J, Nagda JV, Aner M, Bajwa ZH. Response to pulsed and continuous radiofrequency lesioning of the dorsal root ganglion and segmental nerves in patients with chronic lumbar radicular pain. Pain Physician 2008;11:137-44.