Clinical, neurophysiological and neurochemical effects of non-invasive electrical brain stimulation in fibromyalgia syndrome -a systematic review and metaanalysis

Christine Winterholler¹Maria Helena Coura²Pedro Montoya^1*

• ¹University of the Balearic Islands, Palma de Mallorca, Spain
• ²Universidade Nove de Julho, São Paulo, São Paulo, Brazil

Anodal tDCS led to significant reductions in pain intensity and improvements in mood, particularly when applied over the M1 or DLPFC. However, these effects were often short-term, highlighting the need for further research on durability.Longer interventions (e.g., ≥4 weeks) and repeated sessions produced stronger and more lasting effects. However, variability in stimulation parameters and outcome measures limited comparability across studies.Both subjective (e.g., VAS, NRS) and objective assessments (e.g., QST) indicated pain reduction following tDCS, supporting its impact on both sensory and affective pain components.Some studies showed improvements in executive function and memory-mainly when paired with cognitive training-but overall effects on quality of life were mixed.Modulation of β-endorphins, Glx, cortical excitability, and thalamocortical connectivity suggest that tDCS may influence neuroplasticity and central sensitization. However, findings were inconsistent and require further validation.Differences in methodological quality, small sample sizes, and inconsistent use of intention-to-treat analysis limit the strength of conclusions and underscore the need for greater rigor in future research.Future studies should adopt larger samples, harmonized protocols, and longer follow-up periods to better assess long-term efficacy and generalizability.While statistically significant effects were found, most studies did not evaluate whether improvements met thresholds for clinical significance (e.g., Minimal Clinically Important Difference). This limits interpretation of practical benefits and highlights a key gap for future research.