|POSSIBLE USES OF PULSED RADIOFREQUENCY |
Radiofrequency (RF) treatment is a minimally invasive procedure that has been used for over three decades in treating various chronic pain syndromes such as trigeminal neuralgia, post-herpetic neuralgia, low back pain (LBP), and complex regional pain syndrome/reflex sympathetic dystrophy. It is a palliative treatment not without complications. Radiofrequency procedures have been reported to be associated with high number of complications compared with other ablative neurosurgical techniques. Furthermore, conventional (continuous) RF treatment occasionally results in worsening and even new onset of pain. The use of pulsed radiofrequency (PRF, also known as cold RF), a non- or minimally-neurodestructive and thus less painful technique, serves as an alternative to conventional RF therapy. Pulsed radiofrequency treatment, performed under fluoroscopic guidance, entails the use of pulsed time cycle that delivers short bursts of RF energy to nervous tissue.
The available evidence on the effectiveness of PRF in the treatment of patients with various chronic pain syndromes is largely based on retrospective, case series studies. Its clinical value needs to be examined in well-designed, randomized controlled trials with large sample size and long-term follow-up.
Pevzner and co-workers (2005) reported the findings in 28 patients (LBP = 20, cervical pain = 8; average age of 56.7 years) who were treated by PRF and followed for 3, 6 and 12 months. The 3-month follow-up revealed the following results: excellent results in 2 cases (7.1 %), good results in 12 cases (42.9 %), fair in 9 (32.1 %), and 5 (17.9 %) reported that their condition have not changed. Results after 6 and 12 months were excellent in 2 (both groups), good in 7 and 6 respectively, 11 fair (both groups), and unresponsive to treatment was noticed in 8 patients after 6 and 9 patients after 12 months. Significant reduction was found in the visual analog scale (VAS) for pain from an average of 8.8 to 4.2 after 3 months, 4.8 after 6 months and 4.9 after 1 year. The authors concluded that PRF is a safe and simple procedure to control radicular pain in the lumbar and cervical regions. Moreover, they emphasized the need for further prospective, double-blind studies to better ascertain the clinical value of this technique.
Bayer and associates (2005) evaluated the effectiveness of spheno-palatine ganglion PRF (SPG-PRF) treatment in patients suffering from chronic head and face pain. A total of 30 patients were observed from 4 to 52 months after PRF treatment. The primary outcome measures were reduction in oral medication use (including opioids), time to next treatment modality for presenting symptoms, duration of pain relief, and the presence of residual symptoms. Secondary outcome measures included the evaluation of adverse effects and complications. All data were derived from patient charts, phone conversations, and clinical follow-up visits. A total of 14 % of respondents reported no pain relief, 21 % had complete pain relief, and 65 % of the patients reported mild-to-moderate pain relief from SPG-PRF treatment. A total of 65 % of the respondents reported mild-to-moderate reduction in oral opioids. None of the patients developed significant infection, bleeding, hematoma formation, dysesthesia, or numbness of palate, maxilla, or posterior pharynx. The authors concluded that these findings suggested that a prospective, randomized, controlled study to confirm the safety and effectiveness of PRF treatment for chronic head and face pain is justified.
Vallejo and co-workers (2006) presented a prospective case series on the treatment of intractable sacroiliac joint (SIJ) dysfunction with PRF denervation (PRFD) of lateral branches from L4 to S3. A total of 126 patients with presumptive SIJ dysfunction based on history and physical examination underwent arthrographically confirmed steroid/local anesthetic SIJ injection. Fifty-two patients (41.3 %) had greater than 75 % pain relief after two consecutive injections, physical therapy, repeated SIJ injections, and/or analgesics. A total of 22 patients failed to respond; these individuals underwent PRFD of the medial branch of L4, posterior primary rami of L5, and lateral branches S1 and S2. Visual analog score (VAS) and quality of life (QOL) assessments were performed before and after treatment. Sixteen patients (72.7 %) experienced "good" (greater than 50 % reduction in VAS), or "excellent" (greater than 80 % reduction in VAS) pain relief following PRFD. Duration of pain relief ranged from 6 to 9 weeks in four patients, 10 to 16 weeks in five patients, and 17 to 32 weeks in seven patients. In addition, QOL scores improved significantly in all measured categories. Six patients (26.1 %) did not respond to PRFD and had less than 50 % reduction in VAS and were considered failures. The authors concluded that PRFD of the lateral branch of the medial branch of L4, posterior primary rami of L5, and lateral branches S1 and S2 is an effective treatment for some patients with SIJ pain unresponsive to other forms of therapy.
Teixeira and Sluijter (2006) stated that intra-discal RF, with the electrode placed in the center of the nucleus pulposus, has been a controversial procedure in patients with discogenic pain. The authors examined the effect of high-voltage, long-duration intra-discal PRF in patients with 1-level discogenic LBP (n = 8), as confirmed by discography. The pain intensity score on a 0 to 10 NRS was used as outcome measure. The mean duration of pain was 6.3 years (range of 0.5 to 16 years, median of 4 years). The mean NRS score was 7.75 (range of 5 to 9). Disc height was reduced 60 % in one patient and up to 30 % in the remaining subjects. A 15-cm, 20-G needle with a 15-mm active tip was placed centrally in the disc. Pulsed radiofrequency was applied for 20 minutes at a setting of 2 x 20 ms/s and 60 V. There was a very significant drop in the NRS scores over the first 3 months (p = 0.0001). On an individual basis, all patients had a fall of the NRS score of at least 4 points at the 3-month follow-up. A follow-up of 12.8 months (range of 6 to 25 months, median of 9 months) was available for 5 patients. All these patients are now pain-free, except for 1 patient with an NRS score of 2. The authors concluded that this method merits a controlled, prospective study.
Lindner et al (2006) noted that the use of PRF for the treatment of lumbar medial branch for facet pain is controversial. These investigators reported the findings of a retrospective study of PRF treatment of the medial branch in 48 patients with chronic LBP. Patients who did not respond were offered treatment with conventional RF heat lesions. Patients with LBP and greater than 50 % pain relief following a diagnostic medial branch block were included in the study. The mean age was 53.1 +/- 13.5 years; the mean duration of pain was 11.4 +/- 10.9 years. Nineteen patients had undergone surgery. Pain scores on a NRS of 1 to 10 were noted before and after the diagnostic nerve block, before the procedure, and at 1-month and 4-month follow-up. PRF was applied for 2 minutes at a setting of 2 x 20 ms/s and 45 V at a minimum of 2 levels using a 22-G electrode with a 5-mm active tip. Heat lesions were made at 80 degrees Centigrade (C) for 1 minute. A successful outcome was defined as a greater than 60 % improvement on the NRS at 4-month follow-up. In 21/29 non-operated patients and 5/19 operated patients, the outcome was successful. In the unsuccessful patients who were subsequently treated with heat lesions, the success rate was 1/6. The authors concluded that the setup of the study did not allow a comparison with the results of conventional/continuous RF (CRF) for the same procedure, other than the detection of an obvious trend. When comparing these findings with various studies on CRF of the medial branch such a trend could not be found. Based on these retrospective data, prospective and randomized studies (e.g., PRF versus CRF) are justified.
In a case series study, Martin and colleagues (2007) reported the effectiveness of PRF in the treatment of patients with lumbosacral spondylosis. This case series reviewed 22 patients who had been previously treated with PRF with good results. Patients who had been prescribed opioids were excluded from this study. During the PRF application, tissue temperature was limited to 43 degrees C. A minimum of 200 mA of current was delivered in each case. The minimum current (at 50 Hz) necessary to stimulate the involved nerve was recorded. The time from PRF treatment until the patient requested a subsequent application was documented. The effective duration of PRF in patients treated for lumbosacral spondylosis ranged from 5 to 18 months (mean +/- SD: 9 +/- 3.7 months; n = 16). Administrations of PRF to dorsal root ganglion (DRG) were effective from 2 to 12 months (7 +/- 3.8 months; n = 8). Similar results were observed when PRF was applied to cervical medial branch nerves, one suprascapular nerve, and one stellate ganglion. The mean sensory stimulation thresholds obtained before treatment ranged from 0.08 V to 0.14 V. The authors concluded that in this select population of patients who did not receive opioids, and had a favorable response to a previous PRF application, the duration of pain relief supported the use of PRF as an effective pain treatment.
In a retrospective study, Abejon and associates (2007) assessed the effectiveness of PRF applied to the lumbar DRG for the treatment of LBP. This study analyzed the findings of 54 patients who underwent 75 PRF procedures. Patients were divided into 3 groups according to the etiology of the lesion: (i) herniated disc (HD), (ii) spinal stenosis (SS), and (iii) failed back surgery syndrome (FBSS). The analgesic effectiveness of the technique was assessed using a 10-point Numeric Rating Scale (NRS) at baseline and, along with the Global Perceived Effect (GPE), at 30, 60, 90, and 180 days. The reduction in pain medications and the number of complications associated with the technique were assessed. A decrease in the NRS score was observed in patients with HD (p < 0.05) and SS (p < 0.001), but not in those with FBSS. The GPE scores confirmed this finding. No complications were noted. The authors concluded that PRF of the DRG was significantly more effective in HD and SS than in FBSS patients. The application of PRF was ineffective in FBSS.
Van Zundert and associates (2007) examined the effect of PRF for the treatment of patients with chronic cervical radicular pain. A total of 23 patients, out of 256 screened, met the inclusion criteria and were randomly assigned in a double-blind fashion to receive either PRF or sham intervention. The evaluation was carried out by an independent observer. At 3-month follow-up, the PRF group showed a significantly better outcome with regard to the global perceived effect (i.e., greater than 50 % improvement) and VAS (i.e., 20 point pain reduction). The quality of life scales also showed a positive trend in favor of the PRF group, but significance was only reached in the SF-36 domain vitality at 3 months. The need for pain medication was significantly reduced in the PRF group after 6 months. No complications were observed during the study period. These findings are in agreement with the results of the authors' previous clinical audit that PRF treatment of the cervical DRG may provide pain relief for a limited number of carefully selected patients with chronic cervical radicular pain as assessed by clinical and neurological examination.
In an editorial that accompanied the study by Van Zundert et al, Jensen (2007) noted that early studies show good short-term results of PRF. However, there is currently insufficient evidence to use PRF routinely for chronic cervical radicular pain. Jensen stated that more research is needed to ascertain the best way to use PRF and its analgesic mechanism. This is in agreement with the observation of Tella and Stojanovic (2007) who stated that more studies are needed to support the routine use of PRF for treating patients with chronic cervical radicular pain.
Cahana and associates (2006) stated that the clinical advantages and mechanisms of PRF remain unclear. These investigators reviewed clinical and laboratory data on PRF. The final analysis yielded 58 reports on the clinical use of PRF in different applications: 33 full publications and 25 abstracts. They also retrieved 6 basic science reports, 5 full publications, and 1 abstract. The authors stated that the accumulation of these data showed that the use of PRF generates an increasing interest of pain physicians for the management of a variety of pain syndromes. Although the mechanism of action has not been fully elucidated, laboratory reports suggested a neurobiological phenomenon altering the pain signaling, which some researchers have described as neuromodulatory. No side effects related to PRF were reported to date. The authors concluded that further research in the clinical and biological effects of this technique is justified.
In a review on PRF treatment, Gallagher (2006) stated that "we should cautiously prescribe this promising intervention following clinical algorithms that are based upon the best clinical evidence available. However, it is critically important to avoid the mistake of creating a "carte blanche" environment for those practitioners who would abuse the privilege and opportunity presented by this new technology, besmirching our credibility and ultimately impeding the opportunity to use this treatment to the benefit of the public. Ultimately, evidence, not reimbursement, should determine whether pulsed radiofrequency finds a place in our clinical toolbox".
It should be noted that the Reflex Sympathetic Dystrophy Syndrome Association (2006) did not recommend PRF for the treatment of patients with complex regional pain syndrome. It stated that future studies may expand on the role of PRF techniques or such unstudied techniques as cryosurgery as alternative therapies to treat patients with sympathetically maintained pain. The Transport Accident Commission, a government-owned organization of the State of Victoria in Melbourne, Australia (2007) does not consider PRF neurotomy/denervation as part of spinal injection therapy.
Malik and Benzon (2007) reviewed the available literature on PRF and determined its clinical efficacy. Their search of the literature yielded 341 citations; and 51 relevant articles were found. There were 4 review articles: 44 articles pertained to the application of PRF by an electrode placed in the vicinity of a neural structure. Of these, only 2 were randomized controlled trials (RCTs). Of the remaining 42 articles, 1 was a non-RCT, 3 were prospective uncontrolled trials: there were 6 retrospective studies, 11 case reports, 8 laboratory studies, 2 position papers, 5 editorials and 7 items of correspondence, while 1 publication reported 2 studies. Three articles pertained to transcutaneous application of PRF. Of the 2 RCTs, 1 reported efficacy of the PRF while the other reported it to be ineffective. The majority of the uncontrolled and observational studies reported clinical efficacy of PRF, however many of these studies had limitations. The authors concluded that further RCTs are needed for pain physicians to clearly understand the role of PRF in the treatment of various chronic pain syndromes. Furthermore, these investigators (Malik and Benzon, 2008) stated that larger RCTs are needed to (i) assess the long-term effects of RF applications (pulsed and continuous mode) to dorsal root ganglia and (ii) determine the precise mode of action of this trechnique.
Simopoulos and colleagues (2008) prospectively evaluated the response and safety of pulsed and continuous RF lesioning of the dorsal root ganglion/segmental nerves in patients with chronic lumbosacral radicular pain. A total of 76 patients with chronic lumbosacral radicular pain refractory to conventional therapy met the inclusion criteria and were randomly assigned to 1 of 2 types of treatment, PRF lesioning of the dorsal root ganglion/segmental nerve or PRF followed immediately by continuous RF. Patients were carefully evaluated for neurological deficits and side effects. The response was evaluated at 2 months and was then tracked monthly. A Kaplan-Meier analysis was used to illustrate the probability of success over time and a Box-Whisker analysis was applied to determine the mean duration of a successful analgesic effect. Two months after undergoing RF treatment, 70 % of the patients treated with PRF and 82 % treated with pulsed and continuous RF had a successful reduction in pain intensity. The average duration of successful analgesic response was 3.18 months (+/- 2.81) in the group treated with PRF and 4.39 months (+/- 3.50) in those patients treated with pulsed and continuous RF lesioning. A Kaplan-Meier analysis illustrated that in both treatment groups the chance of success approached 50 % in each group at 3 months. The vast majority of patients had lost any beneficial effects by 8 months. There was no statistical difference between the 2 treatment groups. No side effects or neurological deficits were found in either group.
The authors concluded that pulsed mode RF of the dorsal root ganglion of segmental nerves appears to be a safe treatment for chronic lumbosacral radicular pain. A significant number of patients can derive at least a short-term benefit. The addition of heat via continuous radiofrequency does not offer a significant advantage. A RCT trial is now required to ascertain the effectiveness of PRF.
Byrd and Mackey (2008) stated that the mechanism by which PRF controls pain is unclear, but it may involve a temperature-independent pathway mediated by a rapidly changing electrical field. Although much anecdotal evidence exists in favor of PRF, there are few quality studies substantiating its utility.
In a pilot study, Misra et al (2009) evaluated the effectiveness of PRF of spermatic cord in the treatment of chronic testicular pain. A total of 10 patients with chronic testicular pain were treated with PRF stimulation of the spermatic cord. A RF probe placed percutaneously into the spermatic cord was used to deliver four 120-second cycles of 20-millisecond pulses at 2 Hz. Test stimulation was first used to confirm the precise placement of the probe. The short-form McGill Pain Questionnaire was used to assess pain before treatment and at 3 months. Patients who had experienced improvement were followed-up by telephone, to determine if pain relief was sustained. Ten patients were entered into the study but 1 was lost to follow-up. Of the 9 patients evaluated, 4 had complete resolution of pain, while 1 had partial pain relief. Three patients experienced no change and 1 reported that his pain was worse. All patients who experienced complete and partial pain relief continued to do so at a mean long-term follow-up of 9.6 months (range of 3 to 14 months). There were no complications observed immediately or during the follow-up period. The authors reported that pain scores improved in 5 out of 9 patients. They concluded that PRF of spermatic cord appears to be a safe minimally invasive outpatient procedure that should be investigated further with placebo-controlled trials.
In a case series study, Tamimi and colleagues (2009) examined the use of PRF in the treatment of myofascial trigger points and scar neuromas. A total of 9 patients were treated over an 18-month period. All patients had longstanding myofascial or neuromatous pain that was refractory to previous medical management, physical therapy, and trigger point injections. Eight out of 9 patients experienced 75 to 100 % reduction in their pain following PRF treatment at initial evaluation 4 weeks following treatment. Six out of 9 (67 %) patients experienced 6 months to greater than 1 year of pain relief. One patient experienced no better relief in terms of degree of pain reduction or duration of benefit when compared with previous trigger point injections. No complications were noted. The authors stated that these findings suggested that PRF could be a minimally invasive, less neurodestructive treatment modality for these painful conditions and that further systematic evaluation of this treatment approach is needed.
Basal et al (2010) noted that premature ejaculation (PE) is the most common sexual problem experienced by men, and affecting 20 to 30 % of them. Pulsed radiofrequency neuromodulation has been stuided as a treatment for various pain conditions. These researchers used PRF to treat PE by desensitizing dorsal penile nerves in patients resistant to conventional treatments. A total of 15 patients with a lifelong history of PE, defined as an intra-vaginal ejaculatory latency time (IELT) of less than 1 min that occurred in more than 90 % of intercourses and resistant to conventional treatments, were enrolled in this study. Patients with erectile dysfunction were excluded. The mean age of the patients was 39 +/- 9 years. Before and 3 weeks after the treatment, IELT and sexual satisfaction scores (SSS) (for patients and their partners) were obtained. The mean IELT before and 3 weeks after procedure were 18.5 +/- 17.9 and 139.9 +/- 55.1 seconds, respectively. There were no side effects. Mean SSS of patients before and after treatment were 1.3 +/- 0.3 and 4.6 +/- 0.5 and mean SSS of partners before and after treatment were 1.3 +/- 0.4 and 4.4 +/- 0.5 respectively. In all cases, IELT and SSS were significantly increased (p < 0.05). None of the patients and their wives defined any treatment failure during the follow-up period. The mean follow-up time was 8.3 +/- 1.9 months. The authors stated that it is early to conclude that this new treatment modality might be used widely for the treatment of PE, however being an innovative modality, placebo controlled studies (e.g., sham procedure), with larger number of patients, including assessment of penil sensitivity (e.g., biothesiometry) are needed.
Pudendal neuralgia (PN) involves severe, sharp pain along the course of the pudendal nerve, often aggravated with sitting. The ideal management for PN has not been determined. Rhame and colleagues (2009) presented a case of a female with 1.5 years of sharp, burning pain of the left gluteal and perineal regions. She could not sit for longer than 10 to 15 mins. Sacroiliac joint, epidural, and piriformis injections did not improve her pain. She had tried acupuncture, massage, occupational therapy, and physical therapy but the pain persisted. Medication treatment with amitriptyline, gabapentin, extended release morphine sulfate, and oxycodone-acetaminophen provided only minor relief and she had failed other multi-analgesic therapy. She had been unable to work at her desk job for over 1 year. She had a positive response to 2 diagnostic pudendal nerve blocks with lidocaine that provided pain relief for several hours. This patient elected to undergo PRF of the left pudendal nerve in hopes of achieving a longer duration and improved pain relief. Pulsed RF was performed at a frequency of 2 Hz and a pulse width of 20 milliseconds for a duration of 120 seconds at 42 degrees Celsius. After the procedure, she reported tolerating sitting for 4 to 5 hrs. Her multi-analgesic therapy was successfully weaned. At 5 months follow-up, she felt motivated to return to work. One and a half years after the procedure the patient is only taking oxycodone-acetaminophen for pain relief and still has good sitting tolerance. There were no procedure-related complications. To the authors'r knowledge PRF for the treatment of PN has not been reported elsewhere in the literature. It is a relatively new procedure and is felt to be safer than continuous RF. Current literature suggests that PRF delivers an electromagnetic field, which modifies neuro-cellular function with minimal cellular destruction. The authors concluded that PRF of the pudendal nerve offers promise as a potential treatment of PN that is refractory to conservative therapy.
Vanelderen et al (2010) reported on the results of a prospective trial with 6 months of follow-up in which PRF treatment of the greater and/or lesser occipital nerve was used to treat occipital neuralgia. Patients presenting with clinical findings suggestive of occipital neuralgia and a positive test block of the occipital nerves with 2 ml of local anesthetic underwent a PRF procedure of the culprit nerves. Mean scores for pain, quality of life, and medication intake were measured 1, 2, and 6 months following the procedure. Pain was measured by the visual analog and Likert scales, quality of life was measured by a modified brief pain questionnaire, and medication intake was measured by a Medication Quantification Scale. During a 29-month period, 19 patients were included in the study. Mean VAS and median Medication Quantification Scale scores declined by 3.6 units (p = 0.002) and 8 units (p = 0.006), respectively, during 6 months. Approximately 52.6 % of patients reported a score of 6 (pain improved substantially) or higher on the Likert scale after 6 months. No complications were reported. The authors concluded that PRF treatment of the greater and/or lesser occipital nerve is a promising treatment of occipital neuralgia. They stated that this study warrants further placebo-controlled trials.
In summary, there is currently insufficient evidence to support the use of PRF in the treatment of various chronic pain syndromes. Well-designed studies (prospective, randomized, placebo-controlled trials with large sample size and long-term follow-up) are needed to ascertain the clinical value of this approach.
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