Neuroinflammatory effects of radiofrequency

In this issue, you will find a paper by Choi et al. (2014), entitled ‘Inflammatory responses and morphological changes of radiofrequency-induced rat sciatic nerve fibers. ’ The paper describes a preclinical study comparing the anatomical and biological effects of radiofrequency treatment on the sciatic nerve of rats using clinically relevant continuous and pulsed mode protocols. Much has been written about the clinical utility of both techniques and there is a great divide among practitioners regarding the value of pulsed mode radiofrequency treatment for appropriate chronic pain conditions. In the United States, many interventional pain physicians may eschew the use of pulsed radiofrequency because of lack of reimbursement from medical insurance companies compounded by mostly poorly designed or under-powered clinical studies (Bogduk, 2006). Proponents of the pulsed mode laud the potential safety benefits of avoiding high-temperature coagulation of nervous tissue as occurs with continuous mode, theoretically limiting adverse side effects and permitting application of radiofrequency electrical current delivery to treat pain emanating from peripheral nerves with important motor functions as well (Sluijter and van Kleef, 2007). The study by Choi et al., in this issue, adds to the mounting preclinical evidence that pulsed radiofrequency produces quantifiable anatomical and functional effects on nerve function. While there are many other studies that have documented alterations in cellular structure and/or function after both types of radiofrequency protocols, this study is important in that it adds further evidence that (1) although both pulsed and continuous radiofrequency treatments produce alterations in neuroanatomy, disruption of cellular structure is much more severe and persistent after continuous than pulsed delivery of radiofrequency electrical current to the nerve; and (2) the degree and duration of anatomical effects produced by the two distinct types of radiofrequency protocols are paralleled by proportionate levels of immune cell activation and proinflammatory cytokine elaboration in the spinal cord. A logical interpretation of these results is that high-temperature coagulative lesioning of peripheral nervous tissue, as occurs during continuous radiofrequency treatment, leads to a sustained, proinflammatory immune response in the spinal cord that is much diminished in amplitude and duration if pulsed mode is utilized. The extolled safety virtues of pulsed compared with continuous radiofrequency treatment can be measured as both a reduction in motor complications and a reduction in the incidence of deafferentation syndrome (although it has yet to be documented in a head-to-head comparison of both techniques). This study provides further preclinical justification for both propositions, and some of the first evidence that peripheral continuous radiofrequency lesions initiate a robust and sustained glial inflammatory response in the central nervous system. The latter observations are particularly important. Glial activation and cytokine elaboration have recently been implicated as playing pivotal roles in many animal models of chronic pain, most particularly following peripheral nerve injury (Watkins et al., 2007). The activation of this particular proinflammatory and ‘pro-pain’ mechanism by continuous radiofrequency may appear at first glance to be counterintuitive and contrary to the purpose of radiofrequency treatments for chronic pain conditions in general. However, this may be one potential explanation of paradoxical increases in pain seen in patients after radiofrequency treatments. The clinical effect of continuous radiofrequency treatment may therefore reflect a balance between analgesia produced by deafferentation-induced reduction in nociceptive input to the central nervous system and stimulation of proinflammatory, pronociceptive glial activation in the central nervous system as a consequence of deafferentation. Clinical experience indicates that analgesia is more commonly the result; however, central immunemediated inflammation may predominate in patients who experience an increase in pain following the procedure. It is important to note that in this study, no prior intervention was performed to the animals; therefore, the described effects are on naïve animals