Anodal tDCS Improves Poststroke Upper Limb Spasticity, Further Evaluation Needed

Current evidence showed little knowledge about the long-term effects of transcranial direct current stimulation in improving patients poststroke.

A recently published meta-analysis indicated that anodal transcranial direct current stimulation (tDCS), when used as an adjunct intervention, may be an effective and safe method to improving upper limb poststroke spasticity when applied for more than 20 minutes in subacute and chronic stroke survivors aged less than 60 years. However, investigators noted that the evidence was “low-quality,” with little still known about its long-term effects.1

Senior author Ziqi Zhao, DPT, Department of Rehabilitation Medicine, Sichuan University, and colleagues concluded that the results, "do not support the use of transcranial direct current stimulation in isolation; however, it does not compromise its [use in] clinical practice, as transcranial direct current stimulation is usually considered an adjuvant therapy."

The investigators compiled 13 randomized clinical trials, comprising of 924 patients, that explored the effects of tDCS on poststroke spasticity. One randomized trial that compared tDCS combined with virtual reality was not included in the final analysis. Pooled-effect estimates were calculated by comparing the difference in final measurements between the intervention and control groups. When used in combination with other treatment modalities, investigators observed low-quality evidence that tDCS was associated with a decrease in muscle spasticity when compared with the control groups (mean difference, ­–0.91 [95% CI, ­–1.63 to –0.19]).

With the mixed results, Zhao et al concluded, "there is a need for further well-designed research to comprehensively explore the effect of transcranial direct current stimulation on post-stroke spasticity, as well as the function and activities of daily living. Future research is needed to assess patients with stroke using more specific and reliable indicators or methods and to investigate the therapeutic mechanism and find an optimal treatment protocol."1

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The intervention was found to be superior to the control treatments for subacute (standard mean difference, –1.16 [95% CI, ­–1.75 to –0.57) and chronic stroke (standard mean difference, –0.68 [95% CI, –1.13 to –0.22) in patients younger than 60 years (standard mean difference, –1.07 [95% CI, –1.54 to –0.60]). The inclusion of tDCS was not more effective than control treatments for patients older than 60 years.

The superiority of anodal stimulation in improving poststroke spasticity was shown in 6 studies; however, the inclusion of cathodal stimulation in other treatments was not better than that of the control treatments. The remaining 3 studies applied dual stimulation to patients with post-stroke spasticity and did not show a significant difference. Data from the excluded study showed that a combination of tDCS with virtual reality achieved significant improvement in curative effects when compared with the other treatments.

Investigators noted that the strength of the review was that it included the most relevant randomized clinical trials to date based on the most rigorous inclusion and exclusion criteria for the included randomized trials. The results differed from a previous evaluation conducted in 2016, which found moderate-to-low quality evidence for no effect of tDCS on improving spasticity in people with stroke on 5 included trials.2 Zhao et al explained that there may be differences in results because of their inclusion of additional studies that were performed after the time of the prior-published evaluation.

In 2018, a study published found that tDCS has positive outcomes for patients with poststroke aphasia when used in combination with speech therapy. Compared to sham tDCS, patients administered anodal tDCS during outpatient speech therapy were shown to improve in correct naming exercises by 5.7 more words (standard error [SE], 3.3; 95% CI, –0.9 to 12.3), for a relative increase of 70% in correct-naming for anodal tDCS compared to sham.3

REFERENCES
1. Huang J, Qu Y, Liu L, Zhao K, Zhao Z. Efficacy and safety of transcranial direct current stimulation for post-stroke spasticity: a meta-analysis of randomized controlled trials. Clin Rehabil. Published online August 13, 2021. doi:10.1177/02692155211038097
2. Elsner B, Kugler J, Pohl M, et al. Transcranial direct current stimulation for improving spasticity after stroke: a systematic review with meta-analysis. J Rehabil Med.2016; 48(7):565-570. doi:10.2340/16501977-2097
3. Fridriksson J, Rorden C, Elm J, et al. Transcranial Direct Current Stimulation vs Sham Stimulation to Treat Aphasia After Stroke: A Randomized Clinical Trial. JAMA Neurol. 2018;75(12):1470-1476. doi:10.1001/jamaneurol.2018.2287.