Effect of transcranial Direct Current Stimulation for tinnitus treatment: A systematic review and meta-analysis.

OBJECTIVES: To evaluate the effect of tDCS on tinnitus distress, loudness and psychiatric symptoms. METHODS: A systematic literature search of PubMed, Web of Science, Cochrane Library, VHL, EMBASE, PsycINFO, OVID, and CINAHL databases was carried out on articles published until July 2021. Inclusion criteria were published controlled trials using tDCS intervention with tinnitus patients, using a sham/control group, and measuring tinnitus loudness, distress and/or psychiatric symptoms. A meta-analysis was performed for the overall effect as well as to compare subgroups according to tDCS target (left temporoparietal area (LTA) and dorsolateral prefrontal cortex (DLPFC)). RESULTS: Fourteen articles with 1031 participants were included. Six studies applied tDCS over the DLPFC, six over the LTA and two over both areas. Although the overall meta-analysis showed that tDCS significantly decreased tinnitus loudness (SMD=-0.35; 95%CI=-0.62 to -0.08, p = 0.01) and distress (SMD=-0.50, 95%CI=-0.91 to -0.10, p = 0.02).The subgroup analysis showed a significant effect only for tDCS over LTA for loudness (SMD=-0.46, 95%CI=-0.80 to -0.12, p = 0.009), and no other area resulted in significant change. There was no significant effect of treatment on psychiatric symptoms. CONCLUSION: tDCS may improve tinnitus loudness and distress with a small to moderate effect size. Despite the overall positive effect, only LTA tDCS yielded a significant effect. Further well-controlled studies with larger sample sizes and broader exploration of tDCS montages and doses are warranted.

Comparison of two tDCS protocols on pain and EEG alpha-2 oscillations in women with fibromyalgia.

Transcranial Direct Current Stimulation (tDCS) has been used as an alternative treatment for pain reduction in fibromyalgia. In this study, in addition to behavioral measures, we analyzed oscillations in alpha 2 frequency band in the frontal, occipital, and parietal regions, in response to the application of two neuromodulation protocols in fibromyalgia. The study was a randomized, double-blind, placebo-controlled clinical trial with 31 women diagnosed with fibromyalgia. The participants were allocated to three groups with the anodic stimulation applied on the left motor cortex: Group 1, for five consecutive days; Group 2, for 10 consecutive days; and Group 3, sham stimulation for five consecutive days. Statistical analysis showed a reduction in pain intensity after treatment for groups in general [F (1.28) = 8.02; p = 0.008; η2 = 0.223], in addition to a reduction in alpha 2 in the frontal (p = 0.039; d = 0.384) and parietal (p = 0.021; d = 0.520) regions after the treatment on five consecutive days. We conclude that neuromodulation protocols produced similar effects on pain reduction, but differed with respect to the changes in the alpha 2 frequency band in the frontal and parietal regions.