Stroke is an acute compromise of cerebral perfusion or vasculature; it is considered the second-highest cause of death globally and a main cause of disability. Stroke compromises the normal course of many activities of daily living (ADL). At hospital admission, the majority of patients have problems carrying out ADL, and only one out of three patients attain normal neurological function after rehabilitation treatment. Furthermore, working memory impairment is a frequent issue causing executive dysfunction. In this scenario, rehabilitation aims to help the recovery and to increase functional independence in ADL. Particularly, it plays a main role in the improvement of cognition, which is highly relevant for people who experience a decrease in cognitive abilities, such as memory impairment or neglect. Moreover, modern concepts of rehabilitation place improving cognition as the first research priority in stroke medicine.
Present rehabilitation interventions have limited impact on the above-mentioned impairments. Transcranial direct current stimulation (tDCS) could be used to enhance the effects of those interventions; however, its effects are still unknown.
tDCS is a non-invasive method that modulates cortical excitability employing a direct current to the central nervous system.
This review investigated whether tDCS may reduce impairment in ADL; improve arm and leg function, muscle strength, and cognitive abilities; and reduce the occurrence of dropouts and adverse events.
This review is important for
People with post-stroke impairment in cognitive abilities and who experience limitations in their ADL, their loved ones/caregivers, health professionals caring for this population, general practitioners, researchers, and policymakers.
Outcomes of this review
This is an update of Cochrane Systematic Reviews (CSRs) published in 2013 and in 2016. The outcomes analysed were improvement in ADL, upper and lower limb function, muscle strength, cognitive activity, and safety. The CSR included 67 studies published and/or registered up to January 2019, with 1,729 adult participants. Results showed that, compared to any active or passive intervention or placebo, tDCS might improve ADL. Upper and lower limb function was not increased, and the same results were observed for muscle strength and cognitive abilities. The number of adverse events and dropouts were comparable between groups.
These results must be interpreted with caution because: (i) The included trials were heterogeneous for type, location, and duration of treatment; (ii) The treatment also differed for electrode dimensions and placement and the amount of current delivered; (iii) The participants differed for the location of stroke as being cortical or subcortical, which could have produced a false-negative finding; (iv) The studies involved mostly patients with first-time stroke, and most of those patients had an ischaemic type of stroke. This could limit the applicability of the results for patients with recurrent and haemorrhagic strokes. Lastly, evidence is inadequate for lower limb function, cognition, and the reporting of adverse events.
Author’s conclusion of the review
People after stroke who receive tDCS may improve ADL outcomes compared to control (very low to moderate quality of evidence), but these results could not be confirmed after including only trials with appropriate concealment allocation in a sensitivity analysis. Furthermore, tDCS treatment had no effect on upper and lower limb function, muscle strength, and cognitive abilities (low to high-quality evidence). The authors were uncertain whether tDCS improves hemispatial neglect as the evidence has been assessed as very low quality. tDCS probably does not increase the occurrence of dropouts or adverse events (moderate quality of evidence).
Future recommendations
The authors recommended that further large-scale randomized controlled trials (RCT) with parallel-group design and sample size evaluation are necessary. These studies should focus on (a) the methodology specifically regarding allocation concealment and intention to treat analysis, (b) adherence to CONSORT recommendations, and (c) reporting the number of dropouts and adverse events. Cross-over RCTs should also include (d) information on the order of treatment. In conclusion, further studies should examine (e) the effects of tDCS in general application.
Comment by Robin Kuruvila Sentinella