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From the *Pain Management Division, Department of Anesthesiology and Critical Care Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland; Anesthesia Service, Department of Surgery, Walter Reed Army Medical Center, Washington, DC; and Department of Orthopedic Surgery, Stanford, Stanford University School of Medicine, Stanford, CA.
Address correspondence and reprint requests to Steven P. Cohen, Johns Hopkins Pain Management Division, 550 North Broadway, Suite 301, Baltimore, MD 21205. Address e-mail to scohen40{at}jhmi.edu.
Abstract
Nine consecutive patients with discogenic low back pain who obtained excellent pain relief from intradiscal electrothermal therapy were treated with a repeat procedure after the beneficial effects had diminished. Although 4 of 9 patients obtained 
50% pain relief and were satisfied with the results, both the degree and duration of benefit were less pronounced than after the first procedure. Prospective studies are needed to identify the best candidates for repeat intradiscal electrothermal therapy.
Internal disk disruption is a common and refractory cause of chronic low back pain (LBP), with an estimated prevalence rate of 39% (1,2). One treatment that has generated intense interest as a minimally invasive treatment for discogenic LBP is intradiscal electrothermal therapy (IDET). In IDET, a navigable electrothermal catheter is inserted along the inner posterolateral annulus, whereby heating purportedly coagulates nociceptors and granulation tissue, and denatures collagen. Although the reported outcomes of IDET vary widely from <10% (3) to upwards of 80% (4), most studies report approximately 50% intermediate-term success rates in carefully selected patients (5–7).
An inherent difficulty in treating chronic LBP is the high long-term failure rate (8), which often requires repeat interventions. No studies have been published for repeat IDET.
METHODS
Permission to conduct this study was obtained from the Department of Clinical Investigation and from all patients who consented to the procedures. Data were gathered from review of a prospective database set-up for intradiscal procedures and from the charts of all subjects. The records of 247 patients who underwent IDET between 1999 and 2006 were evaluated, among whom nine were identified as having undergone a repeat IDET at the same level(s) as the initial procedure. Reasons why patients did not receive repeat IDET included either failure to obtain relief, or persistent benefit from the first procedure; not currently receiving care in the pain clinic; intervening surgical intervention; patient refusal; lack of preauthorization from third party payer; or patient was deemed a poor candidate for repeat IDET. Our criteria used to establish a diagnosis of discogenic LBP have been described (9,10). These include an abnormal radiologic appearance on magnetic resonance imaging (e.g., endplate signal changes or loss of disk height), 6/10 concordant pain at 
50 psi above opening pressure, and at least one adjacent control disk that failed to elicit pain during disk injection with contrast.
Our inclusion criteria for IDET have also been reported (5). These are chronic LBP >6 mo duration, failure to respond to conservative therapy, 1- or 2-level positive discogram, and absence of focal neurological signs or symptoms. Exclusion criteria are age >60 yr, disk height <50% normal, herniated disk, symptomatic spinal stenosis or spondylolisthesis, and an unstable medical or psychiatric condition.
IDET Procedures
All IDET procedures were performed under sterile conditions with IV sedation (11). Using standard discographic practices, a 17-gauge introducer was inserted into the center of the nucleus pulposus. A 30-cm SpineCATH (Smith Nephew, London, United Kingdom) with a 6-cm electrothermal tip was then inserted through the introducer and advanced circuitously around the posterolateral annulus. After the catheter position was deemed adequate, it was connected to a radiofrequency generator and heating begun using the standard IDET protocol (3–6). After completion of the procedure, patients were given a lumbar support brace and instructed to resume normal activities according to recommended post-IDET recovery guidelines (5).
Outcome Measures
Data were recorded during routine follow-up visits conducted at 1, 3, and 6 mo post-IDET. Follow-up visits done after 6 mo were on an "as needed" basis. The primary outcome measure was the average visual analog scale (VAS) pain score measured 6 mo postprocedure, considering pain during activity, at rest, and with exacerbations. Secondary outcome measures included reduction in analgesic intake (designated as a sustained 20% reduction in opioid usage or complete cessation of a non-opioid analgesic), and global perceived effect (GPE). GPE was recorded based on the response to three questions administered to all patients at each visit:
An affirmative response to all three of these questions at 6 mo and all prior follow-up visits was considered a positive GPE. A successful procedure was defined as a 50% decrease in pain score lasting at least 6 mo postprocedure and a positive GPE.
RESULTS
The mean age of the nine patients was 46 yr (sd, 8.8), and the duration of pain from onset to the first IDET was 6.4 yr (sd, 4.8). Six were male, and three were female. Five patients underwent single-level IDETs, and four had two levels heated (Table 1).
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Overall, four patients (44%) achieved 50% pain reduction lasting at least 6 mo coupled with a positive GPE after their second IDET (Table 2). These successes were equally divided between single and two-level repeat procedures. The mean VAS pain scores before and after the second IDET were 7.1 (sd, 1.2) and 4.6 (sd, 2.4), respectively. Plugging in "0" as the value for patients who obtained <10% pain reduction, the average duration of pain relief after the second IDET was 7.7 mo (sd, 7.7). Two of eight patients who were taking non-opioid analgesics were able to discontinue them. Both active duty personnel remained on active duty through their final follow-up.
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In the five patients who underwent a repeat single-level IDET, the mean VAS pain scores before and after the second procedure were 7.2 (sd, 1.1) and 4.4 (sd, 2.4), respectively. In the four patients who underwent a 2-level IDET, the mean preprocedure pain score was 7.0 (sd, 1.4), which declined to 4.8 (sd, 2.8) 6 mo after the procedure. The average time intervals between the first and second IDETs were 1.9 yr (sd, 0.8) for single-level procedures and 2.6 yr (sd, 2.0) for bi-level treatments.
Despite the significant pain reduction with the second IDET, both the degree and duration of pain relief tended to be less pronounced than after the initial procedure (Figs. 1 and 2). The mean duration of pain relief after the second procedure was 5.4 mo (sd, 7.5) in single-level cases and 10.5 mo (sd, 7.9) for patients who had two discs heated. However, after the first procedure, the mean duration of pain relief was 15.6 mo (sd, 8.3) after one-level IDETs and 23.8 mo (sd, 24.2) after 2-level therapy. No complications were reported during the procedures.
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The results of this case series are mixed. Although four of nine patients achieved significant improvement lasting at least 6 mo, both the degree and duration of pain relief after the repeat IDET were less than after the initial procedure.
The mechanisms by which IDET ostensibly exerts its analgesic effects include nociceptor denervation, collagen denaturation, and the sealing of annular tears (12–14). However, the basic science evidence is conflicting. In a cadaveric study by Bono et al. (12), the authors found that temperatures sufficient to alter collagen architecture (>60°C) were consistently achieved between 2 and 4 mm from the catheter, and temperatures sufficient to coagulate nociceptors (>45°C) were obtained between 9 and 14 mm from the catheter. Yet, in an earlier study, Kleinstueck et al. (15) noted that temperatures needed to induce collagen shrinkage were reliably obtained only 1–2 mm from the electrode. Inconsistent findings have also been noted for post-IDET spinal stability assessments (16,17).
Clinical studies have yielded similarly mixed results. Most studies have demonstrated at least moderate benefit from IDET (7), whereas the two published controlled studies were evenly split between success and failure (3,6). Most, but not all, review articles have concluded that there is moderate-to-strong evidence supporting IDET for discogenic LBP (7,18).
The results of this study indirectly support multimodal mechanisms of action for IDET. If nociceptor coagulation were the sole mechanism for the analgesic effects of IDET, one would not expect any decrement in pain relief from successive procedures, similar to what is observed with facet denervation (19). Alternatively, if collagen denaturation were the sole mode of action for IDET, one might anticipate seeing minimal benefit from repeat procedures. Whereas protein denaturation can in some instances be partially reversible, in most cases the effects are permanent.
Several flaws in this study need to be addressed. First, because data were collected from patient records and a prospectively maintained database, some of the clinical variables analyzed were selected post hoc. Second, this series contained no objective documentation of functional improvement. Although a perfect correlation was found between our main outcome measure and GPE, none of these questions have been validated in formal studies. Our modest results should thus be viewed cautiously, given the high expectation bias that accompanies any invasive procedure, especially one that was previously deemed successful.
In conclusion, the results of this study show that although some patients may benefit from repeating the IDET procedure, the pain reduction may be less pronounced and shorter-lived than after the initial procedure. Prospective studies are necessary to confirm our results and to identify the best candidates for repeat IDET.
Footnotes
Accepted for publication April 10, 2007.
Funded in part by the John P. Murtha Neuroscience and Pain Institute, Johnstown, PA, through the Army Regional Anesthesia and Pain Management Initiative.
The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.
REFERENCES
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