Efficacy and cortical mechanisms of repetitive peripheral magnetic stimulation in non-specific neck and low back pain: a prospective, two-center, randomized, sham-controlled fNIRS study

Non-specific neck (NNP) and low back pain (NLBP) pose significant global health challenges. Current treatment options often result in insufficient outcomes, either due to limited efficacy or adverse side effects. This two-center, randomized, sham-controlled trial utilized functional near-infrared spectroscopy (fNIRS) to explore the immediate analgesic effects and underlying cortical mechanisms of repetitive peripheral magnetic stimulation (rPMS), a non-invasive physiotherapy technique, in patients with NNP and NLBP. A total of 181 patients (75 NNP, 106 NLBP) were randomized to receive either a single session of active or sham rPMS (10 Hz, 100% RMT, 1200 pulses) targeted at the most painful neck or lower back area. The primary outcome measured was the change in pain intensity on the numerical rating scale (NRS), while secondary outcomes included the pressure pain threshold (PPT). Cortical hemodynamic activity was assessed using fNIRS over the dorsolateral prefrontal cortex (DLPFC) and other pre-defined pain-processing regions. Active rPMS resulted in significantly greater analgesia compared to sham stimulation, as indicated by a notable decrease in NRS scores and an increase in PPT (both P < 0.001). fNIRS revealed differential neuromodulatory effects: active rPMS significantly reduced pain-evoked activation in the left DLPFC (L-DLPFC) in NNP patients and bilaterally in NLBP patients. Pooled analysis revealed robust bilateral prefrontal inhibition (L-DLPFC, P = 0.003; R-DLPFC, P = 0.033). There was a significant pre-to-post reduction in DLPFC activation only in the active rPMS group. Interestingly, in the NNP group, ΔNRS were correlated with ΔL-DLPFC (r = 0.313, P = 0.006), and the NLBP group showed bilateral correlations, with ΔNRS associated with both ΔL-DLPFC (r = 0.226, P = 0.020) and ΔR-DLPFC (r = 0.298, P = 0.002). Furthermore, the pooled analysis of all subjects demonstrated a significant bilateral relationship between ΔNRS and ΔDLPFC (ΔL-DLPFC: r = 0.257, P < 0.001; ΔR-DLPFC: r = 0.244, P = 0.001). A single session of rPMS offers rapid and effective analgesia for both NNP and NLBP by modulating DLPFC activity. Our findings underscore a central neuromodulatory mechanism and suggest that the DLPFC may serve as a promising target for non-invasive brain stimulation therapies in the management of NNP and NLBP. The Ethics Review Committee of the Xijing Hospital Affiliated to Air Force Medical University, No. KY-20222009-F-1; www.chictr.org.cn, ChiCTR2200060844, Date of Registration: 12 June 2022.