The effects of pulsed radiofrequency fields applied to the dorsal root ganglion - a preliminary report

While making a radiofrequency (RF) lesion the tissue which surrounds the tip of the electrode is exposed to an electromagnetic field (EMF). This EMF might be instrumental in causing the clinical effect of RF lesions. This article reports two studies which were undertaken to investigate the role of EMF as opposed to the effect of heat. To apply EMF without raising the tip temperature of the electrode, continuous RF can be applied at a low output setting of the generator or alternatively pulsed RF can be used to combine a voltage output which is normally used when making RF heat lesions with a low tip temperature. In the first study the short-term clinical effect of a 42 degrees C lesion was investigated with conventional, continuous RF vs a lesion with pulsed RE It was found that the clinical effect of pulsed RF was superior: 56% of patients had a global perceived effect of more than 75% as compared with 4% when using continuous RF. The second study was undertaken to investigate the usefulness of future double blind studies. It was an open prospective pilot study of the effect of pulsed RF adjacent to the dorsal root ganglion in patients with failed back surgery with unilateral symptomatology. Following diagnostic segmental nerve blocks a maximum of two levels was treated. Out of 20 patients 5 did not respond to any diagnostic block. In the remaining 15 patients treatment was successful in 8 patients at 6 months follow-up. 2 of those patients had a recurrence of pain at 12 months follow-up. It is concluded that the EMF may be instrumental in causing the clinical effect of the RF lesion adjacent to the dorsal root ganglion. Calculations are presented to support the hypothesis that the effect of EMF should be attributed to the electrical field since the magnetic field is of insignificant intensity.