Numerous studies have investigated the effects tDCS on cortical excitability in healthy subjects. However, the relationship of physiological changes due to tDCS stimulation in individuals with SCI remains unclear. As such, two studies recently investigated the effects of tDCS in chronic SCI patients for rehabilitation of upper extremity motor function.
In one RCT, Cortes and colleagues investigated the effects of one session of 1 mA, 2 mA and sham anodal tDCS on upper extremity motor performance (hand grasp and release) in patients with chronic cervical SCI. Although clinical assessment of hand function using the box and blocks test showed no difference between groups, a significant improvement in hand grasp was observed in the 2 mA group. This suggests that a single session of 2 mA tDCS may improve hand motor function, although future studies are necessary to determine whether tDCS may be an effective long-term rehabilitation strategy. Correspondingly, Potter-Baker et al. investigated the effects of pairing tDCS with massed practice rehabilitation training for several sessions over two weeks. Significant improvements in muscle strength were observed in weak proximal, wrist and hand muscles; however, no difference was observed between groups in clinical assessments. The lack of statistical significance may be due to the relatively small sample size. Despite this, the relative ease of integrating tDCS into routine clinical training for upper extremity rehabilitation in SCI patients, and the associated improvements in hand grasp/muscle strength, suggest further research is warranted. Future clinical trials should evaluate the efficacy of multiple tDCS sessions, as well as robotic-assisted training combined with tDCS.
There is level 1b evidence (from one RCT; Cortes et al., 2017) that a single session of tDCS significantly improves hand grasp in patients with chronic SCI, however, larger clinical trials are necessary to determine the effectiveness of tDCS as a long-term rehabilitation strategy.
There is level 2 evidence (from one cohort study; Potter-Baker et al., 2018) that tDCS paired with massed practice training may provide some advantage in improving the strength of proximial/hand muscles, however, larger clinical trials are necessary.
tDCS may provide some advantage in improving upper extremity muscle strength and hand grasp, however, larger clinical trials are necessary to determine the effectiveness of tDCS as a long-term rehabilitative therapy.