54 Korean J Pain Vol. 25, No. 1, 2012 medial branch, or peripheral nerves. However, it has been rarely used to treat myofascial pain [1]. Myofascial pain is a common pain syndrome. However, long-term treatment of this pain is difficult [2]. Traditional treatment includes using local anesthetics (including ste- roids) injection at trigger points, dry needling, physical therapy, and behavior modification. However, the duration of pain relief is often less than a few days or weeks. Thus, although various methods have been suggested for pro- longed analgesia, none has been found to perform signi- ficantly better than another [2]. Pulsed RF treatment was performed at muscles trigger points to produce prolonged analgesia. Significant an- algesia was obtained for three months after the patient received pulsed RF treatment at both trapezius regions. There is no explanation exists as to why pulsed RF treat- ment has a longer pain relief effect. In case of TPI or dry needling, analgesic effects are brought by a complex mechanism of a stimulus to cutaneous Aδ nerve fiber by needling, a stimulus to C-fiber by local anesthetics in- jection, and an alteration of around the trigger point vari- ous chemical environments (cytokine, substance P, etc.,) which induces pain [2]. Pulsed RF is known to be involved in the expression of the c-fos gene at lamina I and II in the dorsal horn at the neurobiological level [3,4]. The c-fos gene expression encourages the formation of prepro- dinorphin, which is the second RNA messenger. This re- sults in an increased production of endorphin that modu- lates analgesic action [5]. Thus, the change in the gene expression caused by pulsed RF may reflect an inherent change in the dorsal horn, which may cause a prolonged analgesic effect [6]. Additionally, the strong magnetic field formed during pulsed RF treatment might reduce the transmembrane potential of the micro-nerves (Aδ fiber or C-fiber) in or around the muscle, which might have also affected the neuronal environment and thereby influenced the analgesic effect and duration by means of the thermal field effect in tissue [7]. Further studies need to be con- ducted to compare the analgesic effect and duration of TPI and pulsed RF treatment to the muscles in the same regions. In conclusion, pulsed RF treatment has the advantage of not destroying neurons and producing less pain. It can also give a longer analgesic effect than conventional treat- ment methods when applied to myofasical pain. Pulsed RF treatment is cost-effective in view of its use in repeated outpatient visits. More prospective randomized controlled trial studies are necessary to compare its effectiveness with TPI treatment. REFERENCES 1. Tamimi MA, McCeney MH, Krutsch J. A case series of pulsed radiofrequency treatment of myofascial trigger points and scar neuromas. Pain Med 2009; 10: 1140-3. 2. Bevacqua B, Fattouh M. Pulsed radiofrequency for treatment of painful trigger points. Pain Pract 2008; 8: 149-50. 3. Higuchi Y, Nashold BS Jr, Sluijter M, Cosman E, Pearlstein RD. Exposure of the dorsal root ganglion in rats to pulsed radiofrequency currents activates dorsal horn lamina I and II neurons. Neurosurgery 2002; 50: 850-5. 4. Van Zundert J, de Louw AJ, Joosten EA, Kessels AG, Honig W, Dederen PJ, et al. Pulsed and continuous radiofrequency current adjacent to the cervical dorsal root ganglion of the rat induces late cellular activity in the dorsal horn. Anesthe- siology 2005; 102: 125-31. 5. Hunter JC, Woodburn VL, Durieux C, Pettersson EK, Poat JA, Hughes J. c-fos antisense oligodeoxynucleotide increases formalin-induced nociception and regulates preprodynorphin expression. Neuroscience 1995; 65: 485-92. 6. Chao SC, Lee HT, Kao TH, Yang MY, Tsuei YS, Shen CC, et al. Percutaneous pulsed radiofrequency in the treatment of cervical and lumbar radicular pain. Surg Neurol 2008; 70: 59-65. 7. Cosman ER Jr, Cosman ER Sr. Electric and thermal field effects in tissue around radiofrequency electrodes. Pain Med 2005; 6: 405-24.