Abdominal Acupuncture Changes Cortical Responses to Nociceptive Stimuli in Fibromyalgia Patients

Acupuncture is used by one in five fibromyalgia patients within 2 years of diagnosis and has a moderate effect on pain and stiffness compared with no treatment and standard therapy [1]. The mechanism of acupuncture-induced analgesia is likely based on the activation of different types of mechanical and nociceptive fibers that is induced by the insertion of needles into acupoints [2]. The functional state of nociceptive pathways can be evaluated by multichannel laser-evoked potentials (LEPs) [3]. The aim of this study was to evaluate acute changes in multichannel LEPs induced by abdominal acupuncture in a cohort of acupuncture treatment-na€ıve fibromyalgia patients. Ten fibromyalgia patients were diagnosed according to the criteria of Wolfe et al. [4] and agreed to participate in this study, which was approved by local Ethic Committee of Bari Policlinico General Hospital. No patient had any peripheral or central nervous system disease. In the real acupuncture session, needles (40 9 0.2 mm) were inserted according to the abdominal meridian system and turtle system in CV 12, 10, 6, and 4, Ren 13 and 17, and ST 24 and 26 [5]. In the sham acupuncture session, the needles were inserted 3–5 mm away from the acupoints. In both sessions, the needles were inserted for 30 min. Each patient was submitted to real and sham acupuncture session, and the two sessions were separated by at least 15 days to avoid carryover effects. The order of the real and sham acupuncture sessions was randomized among patients. Before needle insertion (baseline condition) and soon after needle removal, 30 CO2 laser stimuli (duration, 25 ms; interstimulus interval, 10 s; wavelength, 10.6 mm) were delivered to each of three sites: the right abdomen near the umbilicus, the dorsum of the right hand, and the skin over the chest tender point [6]. The order of stimulation was randomized among patients. Stimulus intensity was determined on a subject-specific basis and was above the pain threshold. Electroencephalography was recorded throughout the laser stimulation using 62 scalp electrodes positioned according to the enlarged 10–20 system. At the beginning and end of each session, the pain level at tender points was evaluated according to Okifuji et al. [6]. A preliminary EEG analysis was performed by an examiner blinded to the conditions (baseline, sham acupuncture, and real acupuncture) considering the CZ derivation, referred to nasion, and T3, referred to Fz, to evaluate the N2 and P2 vertex components and the N1 temporal component of each LEP [3]. LEPs were analyzed using standardized low-resolution brain electromagnetic tomography (s-LORETA) software [7]. The N2-P2 amplitude obtained by the abdomen stimulation was significantly increased after acupuncture session (repeated-measures ANOVA with condition baseline, sham, acupuncture as factor F = 13.40, df = 2, P = 0.002), while it was reduced after acupuncture when the chest tender point was considered (F = 7.52; P = 0.012). (Table 1). No change was observed on LEPs obtained by the hand. (F = 2.78, n.s.). The subjective laser pain, measured using a visual analogical scale ranging from 0 to 100, did not change among the experimental conditions (F = 0.34, 1.24 and 0.98 for the hand, chest tender point and abdomen, respectively, df = 2, n.s.; Table 1). The voxel-by-voxel log F ratio, employed to detect the dipolar source of LEPs [7], was computed for real acupuncture versus the baseline condition in the time interval of the N2 LEP component (180–250 ms) for abdomen stimulation and in the time window of the P2 LEP component (290–340 ms) for chest tender point stimulation. The N2 component of the potential evoked by abdomen stimulation was higher after real acupuncture than in the baseline condition in the cingulate gyrus (Brodmann area 24) and the inferior operculum (Brodmann areas 40 and 41; Figure 1A). The P2 component of the potential evoked by chest tender point