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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.