Efficacy, safety, and tolerability of bilateral transcranial direct current stimulation combined to a resistance training program in chronic stroke survivors: A double-blind, randomized, placebo-controlled pilot study

Background: Transcranial direct current stimulation (tDCS) is a promising tool for stroke rehabilitation. Yet, so far, results from the available clinical trials are inconclusive. Objectives: The primary objective of the present work was to test the efficacy of multiple sessions of tDCS combined with a highly standardized and progressive resistance training program of the affected upper limb in individuals in the chronic phase of recovery after a stroke. Secondary objectives were to test the safety and tolerability of these combined interventions. Methods: This two-arm parallel pilot trial recruited participants that were >= 18 years old, community-dwelling, and had sustained a supratentorial stroke >= 6 months prior to the study. They were allocated using a stratified randomization into two groups: 1) real tDCS + resistance training and 2) sham tDCS + resistance training. The resistance training program targeted the affected upper limb and consisted in 60 minutes of exercises, 3 times/week over 4 weeks. During each session, participants received either real- or sham-tDCS, using a bi-hemispheric montage for the first 20 minutes, and were blinded to the tDCS intervention. Outcome measures of clinical efficacy (Fugl-Meyer Assessment, Box and Block Test, Wolf Motor Function Test, grip strength, modified Ashworth scale and Motor Activity Log) were assessed by a blinded evaluator before and after the 4-week training program. Safety and tolerability were evaluated, respectively, by the number and characteristics of tDCS adverse events and dropout rates with their reasons. Results: From the 147 individuals screened for eligibility, 14 participants (68.9 +/- 10.0 years old; 70.9 +/- 57.6 months post-stroke) met the selection criteria and were allocated to real-tDCS (n = 7) or sham-tDCS (n = 7) groups. Both groups improved on the clinical outcome measures, but these changes were not significantly different between groups (p > 0.17). No dropout occurred throughout the study. Participants frequently reported mild skin tingling during the administration of both real- and sham-tDCS, and no group difference was noted for its frequency and intensity (p > 0.38). One participant having received real-tDCS complained about a mild skin burning sensation after two sessions. The a priori sample size analysis performed on the Fugl-Meyer Assessment scores revealed that 56 participants would be required in a future clinical trial to reach 80% power at a significance level of 0.05. Conclusions: In this pilot study, repeated sessions of bi-hemispheric tDCS coupled with resistance training were found safe and tolerable for individuals at the chronic phase post-stroke. However, the use of tDCS did not result in additional sensorimotor improvements when compared to sham-tDCS. Further research is needed to better assess the clinical benefits of combining non-invasive transcranial stimulation with rehabilitation after a stroke.