Effects of Different Stimulation Parameters on the Efficacy of Transcranial Direct Current Stimulation for Post-Stroke Dysphagia: An Updated Systematic Review and Meta-Analysis of Randomized Controlled Trials

Aims/Background: Transcranial direct current stimulation (tDCS) is a promising intervention for post-stroke dysphagia (PSD). However, no consensus has been reached regarding the optimal stimulation parameters. This study aimed to identify the optimal tDCS stimulation protocol for patients with PSD. Methods: Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we systematically searched seven databases (Web of Science, PubMed, Embase, Cochrane Library, WanFang, CNKI, and VIP) for relevant trials, covering the period from database inception to 1 January 2025. Statistical analyses were performed with Review Manager 5.40, with the choice of fixed- or random-effects model guided by I2 values. Results: Overall, tDCS significantly improved swallowing function compared with control conditions for both outcome measures in which higher scores indicate better swallowing function (standardized mean difference (SMD) = 1.16, p < 0.001) and those in which lower scores indicate better swallowing function (SMD = −0.85, p < 0.001). In the subgroup analysis by stimulation intensity, 1.4 mA yielded the largest point estimate among positive-direction outcomes (SMD = 1.91, p = 0.04), whereas 1.8 mA yielded the largest effect estimate among negative-direction outcomes (SMD = –0.82, p = 0.04). Both single-session tDCS lasting 20 minutes and 30 minutes significantly improved swallowing function in patients with PSD (positive outcome indicators, 20 min: SMD = 1.18, p < 0.001; 30 min: SMD = 1.28, p = 0.02, subgroup difference: p = 0.86; negative outcome indicators, 20 min: SMD = –0.69, p < 0.001; 30 min, SMD = –0.70, p = 0.005, subgroup difference, p = 0.89). However, prolonging single-session duration to 30 minutes did not confer superior therapeutic efficacy relative to 20 minutes. tDCS was effective for both supratentorial and infratentorial lesions (positive outcome indicators, SMD = 1.57, p < 0.001; negative outcome indicators, SMD = –0.73, p < 0.001). Compared with the control group, swallowing function was improved in acute, sub-acute and chronic stroke patients treated with tDCS intervention (positive outcome indicators, Acute: SMD = 1.17, p < 0.0001; Subacute: SMD = 1.72, p < 0.0001; Chronic: SMD = 0.59, p = 0.0004; negative outcome indicators, Acute: SMD = –0.78, p < 0.0001; Sub-acute: SMD = –0.91, p = 0.0001; Chronic: SMD = –0.77, p = 0.001). tDCS significantly improved swallowing function in patients with pseudobulbar palsy (SMD = –0.86, p = 0.001), whereas it showed no obvious therapeutic effect on patients with bulbar palsy (SMD = –0.48, p = 0.07). Conclusion: tDCS yields favorable effects on swallowing function in patients with PSD when administered to the lesional hemisphere, the contralesional hemisphere, or bilaterally, and there are no differences in efficacy among the three stimulation modes. An intensity of 1.8 mA represents a potential optimal “sweet spot”, suggesting that higher intensities (2.0 mA) do not necessarily translate to better clinical outcomes. A 20-minute session duration is sufficient for therapeutic effect. Systematic Review Registration: PROSPERO (CRD42022344115).