A new approach to assessing blinding for transcranial direct current stimulation treatment in patients with fibromyalgia. A randomized clinical trial

Background. Correct blinding is essential for preventing potential biases. James’ and Bang’s blinding indexes (BIs) are the most widely employed statistical methods for quantifying blinding effectiveness. Up to this date, no randomized clinical trial has assessed the effectiveness of these tools in treatments with transcranial direct current stimulation. The aim of this study was to assess the blinding of participants and therapist following treatment with transcranial direct current stimulation in subjects with fibromyalgia.

Methods. Randomized, triple-blind, sham-controlled, clinical trial. Eighty subjects > 18 years of age and diagnosed with fibromyalgia were enrolled. The intervention lasted two weeks and comprised five sessions of 20-minute stimulation (active or sham). A questionnaire was delivered to both the therapist and patients after the last session to record their guess of which treatment had been applied. To assess the success of blinding, James’ and Bang’s BIs were calculated.

Results. No differences between the groups were noted at baseline in terms of demographic or clinical data. James’ BI was 0.83 (CI 95%: 0.76–0.90) for the patients and 0.55 (CI 95%: 0.45–0.64) for the therapist. Bang’s BI for subjects was -0.08 (CI 95%: -0.24–0.09) and -0.8 (CI 95%: -0.26–0.1) for the active and sham transcranial direct current stimulation groups, respectively. Bang’s BI for the therapist was 0.21 (CI 95%: -0.02–0.43) and 0.13 (CI 95%: -0.09–0.35) for the active and sham transcranial direct current stimulation groups, respectively.

Conclusions. Protocols of active and sham transcranial direct current stimulation applied in this study have shown satisfactory blinding of the therapist and subjects with fibromyalgia.