Acupuncture is a complex multi-component treatment that has shown promise for the treatment of Fibromyalgia (FM), however, clinical trials have shown mixed results, possibly due to heterogeneous methodology and lack of understanding of the underlying mechanism of action. We sought to understand the specific contribution of somatosensory afference to improvements in clinical pain, and the specific brain circuits involved.
76 FM patients were randomized to receive 8 weeks (2 treatments/week) of electroacupuncture (EA, with somatosensory afference) or mock laser acupuncture (ML, with no somatosensory afference). Brief Pain Inventory (BPI) Severity, resting state functional MRI (rs-fMRI), and proton magnetic resonance spectroscopy ( H-MRS) in the right anterior insula (aINS) were collected at pre- and post-treatment.
FM patients receiving EA experienced a greater reduction in pain severity compared to ML (mean difference, EA=-1.14, ML=-0.46, Group x Time interaction, p=0.036). Participants receiving EA, as compared to ML, also displayed increased resting functional connectivity between the primary somatosensory cortical representation of the leg (S1 ; i.e. S1 subregion activated by EA) and aINS. Increase in S1 -aINS connectivity was associated with reductions in BPI severity (r=-0.44, p=0.01) and increases in aINS gamma-aminobutyric acid (GABA+) (r=-0.48, p=0.046) following EA. Moreover, increases in aINS GABA+ was associated with reductions in BPI severity (r=-0.59, p=0.01). Finally, post-EA changes in aINS GABA+ mediated the relationship between changes in S1 -aINS and BPI severity, bootstrapped CI=[-0.533, -0.037].
The somatosensory component of acupuncture modulates primary somatosensory functional connectivity in association with insular neurochemistry to reduce pain severity in FM.

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