Purpose of reviewMyofascial pain syndrome is a chronic pain condition characterized by the presence of myofascial trigger point, a hyperirritable painful spot involving a limited number of muscle fibers. The literature suggest that myofascial trigger points should be considered peripheral pain generators and this critical review will summarize recent findings concerning the clinical evaluation and the treatment of myofascial trigger points. Recent findingsThe clinical features of myofascial trigger points and their contribution to the patient pain and disability have been detailed in several recent studies, which support the clinical relevance of the condition. Recent studies reported that manual palpation to identify MTrPs has good reliability, although some limitations are intrinsic to the diagnostic criteria. During the last decade, a plethora of treatments have been proposed and positive effects on pain and function demonstrated.

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AimsIt is hypothesized that dorsal root ganglion stimulation (DRGS), sharing some of the mechanisms of traditional spinal cord stimulation (SCS) of the dorsal columns, induces γ‐aminobutyric acid (GABA) release from interneurons in the spinal dorsal horn.MethodsWe used quantitative immunohistochemical analysis in order to investigate the effect of DRGS on intensity of intracellular GABA‐staining levels in the L4‐L6 spinal dorsal horn of painful diabetic polyneuropathy (PDPN) animals. To establish the maximal pain relieving effect, we tested for mechanical hypersensitivity to von Frey filaments and animals received 30 minutes of DRGS at day 3 after implantation of the electrode. One day later, 4 Sham‐DRGS animals and four responders‐to‐DRGS received again 30 minutes of DRGS and were perfused at the peak of DRGS‐induced pain relief.ResultsNo significant difference in GABA‐immunoreactivity was observed between DRGS and Sham‐DRGS in lamina 1‐3 of the spinal levels L4‐6 neither ipsilaterally nor contralaterally.ConclusionsDorsal root ganglion stimulation does not induce GABA release from the spinal dorsal horn cells, suggesting that the mechanisms underlying DRGS in pain relief are different from those of conventional SCS. The modulation of a GABA‐mediated “Gate Control” in the DRG itself, functioning as a prime Gate of nociception, is suggested and discussed.

Summary Aims Conventional dorsal root ganglion stimulation (DRGS) is known to achieve better pain‐paresthesia overlap of difficult‐to‐reach areas like the feet compared to dorsal column spinal cord stimulation (SCS). As in painful diabetic polyneuropathy (PDPN) pain is mostly present in the feet, we hypothesized that DRGS is more effective in relieving pain in PDPN when compared to SCS. Methods Diabetes was induced in female Sprague‐Dawley rats with an intraperitoneal injection of 65 mg/kg of streptozotocin (STZ; n = 48). Rats with a significant decrease in mechanical paw withdrawal response to von Frey filaments 4 weeks after injection were implanted with DRGS electrodes (n = 18). Rats were assigned to DRGS (n = 11) or sham‐DRGS (n = 7). Mechanical paw withdrawal thresholds (WT, measured in grams) in response to DRGS (50 Hz, 0.18 ± 0.05 mA) were assessed with von Frey testing. The results of the experiments on these animals were compared to the results of a previous study using exactly the same model on PDPN animals selected for SCS (n = 8) (40‐50 Hz, 0.19 ± 0.01 mA) and sham‐SCS (n = 3). Results In the SCS group, the log10 (10 000 × 50% WT) increased from 4910 to 5211 at t = 15 minutes (P < 0.05) and 5264 at t = 30 minutes (P = 0.11). In the DRGS group, the log10 (10,000 × 50% WT) increased from 4376 to 4809 at t = 15 minutes (P < 0.01) and 5042 at t = 30 minutes (P < 0.01). Both DRGS and SCS induced a similar and complete reversal of mechanical hypersensitivity. After cessation of stimulation (t = 60), the return of the log10 (10 000 × 50% WT) response was significantly faster with DRGS than that of SCS (P < 0.05). Conclusions We conclude that conventional DRGS is as effective as SCS in reduction of PDPN‐associated mechanical hypersensitivity in STZ‐induced diabetic rats. The wash‐in effect of DRGS and SCS was similar, but DRGS showed a faster washout course. Long‐term efficacy should be studied in future animal research.