Therapeutic Effect and Optimal Electrode Placement of Transcutaneous Neuromuscular Electrical Stimulation in Patients with Post-Stroke Dysphagia: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: To date, there is no conclusive evidence that transcutaneous neuromuscular electrical stimulation (TNMES) benefits patients with post-stroke dysphagia (PSD). In addition, the optimal TNMES electrode placement has not been well-established. This systematic review and meta-analysis were conducted to investigate these two research gaps. Methods: Five major databases were systematically searched for randomized controlled trials (RCTs) through January 2022. Effect sizes were computed using Hedges' g statistic, which were then entered into the random-effects model to obtain pooled effect estimates. Results: Twenty-four RCTs met the eligibility criteria. On the improvement of swallowing function, TNMES alone was not superior to conventional swallowing therapies (CSTs); combined therapy of TNMES and CSTs significantly surpassed CSTs alone (standardized mean difference (SMD) = 0.91, 95% confidence interval (95% CI): 0.68 to 1.14, p < 0.0001; I-2 = 63%). Moreover, significant pooled effect sizes were observed in subgroups with horizontal electrode placement above the hyoid bone (SMD = 0.94, 95% CI: 0.72 to 1.16; I-2 = 0%) and horizontal electrode placement just above and below the hyoid bone (SMD = 0.87, 95% CI: 0.59 to 1.14; I-2 = 0%). The largest pooled effect size was observed in the subgroup that individualized electrode placement according to dysphagia evaluation (SMD = 1.65, 95% CI: 0.38 to 2.91; I-2 = 90%). Conclusion: TNMES should be used in combination with CSTs for PSD. Horizontal electrode placement should target suprahyoid muscles or both suprahyoid and thyrohyoid muscles.