Non-Invasive Brain Stimulation for Core Symptoms of Chronic Primary Pain: A Meta-Analysis of RCTs

Background/Objectives: Chronic primary pain (CPP) is a new diagnostic category including chronic pain conditions lacking clinical signs or a clear etiopathogenetic origin. These disorders may share a common neural mechanism known as central sensitization, where nociceptive neurons become hyper-responsive to standard or subthreshold pain stimuli, resulting in pain hyper-sensitivity. In this context, non-invasive brain stimulation (NIBS) appears to be a promising tool for improving CPP symptoms by targeting maladaptive brain activity and connectivity. To date, the effects of NIBS on CPP symptoms remain unexplored. To fill this gap, we conducted a meta-analysis, investigating the effect of NIBS in improving the three core symptoms of CPP, namely pain intensity, emotional distress, and functional disability. Methods: Following PRISMA guidelines, we screened four databases up to February 2025 for English-language, peer-reviewed randomized clinical trials that included CPP patients treated with NIBS and reported pre/post or follow-up scores on validated measures of at least one core symptom. Quality of life was examined as an additional outcome. Results: Fifty-four studies were included, with 1371 participants receiving real stimulation and 1103 sham. Findings highlighted that real stimulation improved CPP symptoms immediately after treatment and at one-month follow-up. Meta-regressions showed that longer CPP duration reduced short-term effects on emotional distress and diminished all outcomes at one-month follow-up. Conclusions: Further research is needed to establish standardized NIBS protocols for CPP management, to investigate the effectiveness at longer follow-up periods, and to test whether combining NIBS with other interventions enhances treatment effectiveness and durability.