From a therapeutic point of view, the treatment of discogenic pain appears to be rather limited. On the one hand, appropriate conservative care (e.g., active physical therapy, pharmacological management) should be expected to yield success in the vast majority of cases. However, failing this, the only other available treatment has been arthrodesis. Clearly, this is a very limited treatment continuum. From a philosophical point
of view, a minimally invasive intradiscal treatment technique is quite attractive in an attempt to extend that continuum. Recent attention has been focused on the use of thermal energy to treat discogenic pain (intradiscal electrothermal therapy, or IDET). Whether the mechanism of action is deafferentative, biomechanical, or both remains to be eluci-dated,65,66 although clinical data suggesting a delayed therapeutic effect after the procedure would suggest the latter. Numerous studies suggest a therapeutic effect.67-70 Although most studies have been prospective cohort controlled, or retrospective, within the limitations of this study design a therapeutic effect comparable to that of arthrodesis has been suggested. One randomized prospective, double-blinded study has been reported to date (at the 2002 annual meeting of the International Spinal Injection Society): Pauza et al. noted a significant effect of treatment at 6 months in the active versus the placebo group.71
In a multicenter study, Wetzel et al.72 reported significant improvement in many functional scales, and a decrease in Visual Analog Scales (VAS). In this particular study, all investigators were surgeons, and all patients who were treated with IDET were considered to be potential surgical candidates. Of the original group, 14 went on to spinal fusion. When this group is compared with those who underwent IDET only (N = 43), similar rates of improvement in terms of functional scores and pain relief were noted. However, when patients were asked specifically whether they felt that the procedure was worthwhile and would consider it again, 61% of the IDET-only group responded positively versus only 27% of the surgical group.
Controversy remains, however, regarding the mechanism of action of intradiscal thermal treatment. Studies investigating the use of thermocouple technology (e.g., IDET) have reported conflicting results. Kleinstueck et al.65 noted variability in outer annular heating, and little or no biomechanical effect acutely, as measured in vitro. The in vitro limitations of this study are apparent, inasmuch as such a study design fails to take into account the ongoing processes of healing. By contrast, Shah et al.66 did demonstrate annular shrinkage, coalescence of collagen, and denaturation in a study of cadaver discs following IDET lesions. Light microscopy demonstrated significant coalescence of collagen, with no evidence of endplate damage. Temperature mapping in this study did suggest that an intradiscal thermocouple raised the temperature significantly across the entire posterior annulus, thereby inducing the observed changes.
From a surgical perspective, the efficacy of intradiscal therapy remains to be proven, although its prospects are encouraging. Clearly, the randomized prospective study methodology such as that of Pauza et al.71 with long-term follow-up will be required to answer this question.
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