Long-term effects of transcranial direct current stimulation (tDCS) combined with speech language therapy (SLT) on post-stroke aphasia patients: A systematic review and network meta-analysis of randomized controlled trials

BACKGROUND: Transcranial direct current stimulation (tDCS) is a noninvasive neuromodulation tool for improving language performance in patients with aphasia after stroke. However, it remains unclear whether it has long-term effects. After consulting a large number of relevant studies, it was found that there are no definitive conclusions about the long-term effects of tDCS on post-stroke aphasia patients. OBJECTIVE: To determine whether tDCS has long-term effects on post-stroke aphasia patients (PAPs) and which type of tDCS has the most beneficial treatment effects on language performance (especially naming ability). METHODS: A network meta-analysis was conducted by searching for randomized controlled trials (RCTs) published until April 2023 in the following databases: Web of Science, Embase, Medline (from OVID and PubMed), PsycInfo and PsycARTICLES (from OVID). We only included RCTs published in English. PAPs treated by tDCS combined with speech-language therapy were selected. Sham tDCS was the control group. Naming ability or other language performance must be assessed at follow-up states. Two reviewers independently used checklists to assess the primary outcome (the long-term effects on naming ability) and the secondary outcome (other language performance, such as communication). Cochrane Collaboration guidelines were used to assess the risk of bias. RESULTS: Seven studies with 249 patients were included for data synthesis. For primary outcomes (naming nous), there was no obvious evidence to show a difference between interventions (C-tDCS vs. S-tDCS SMD= 0.06, 95% CI = -1.01, 1.12; A-tDCS vs. S-tDCS SMD= 0.00, 95% CI = -0.66, 0.65; D-tDCS vs. S-tDCS SMD= 0.77, 95% CI = -0.71, 2.24; A-tDCS vs. C-tDCS SMD= -0.06, 95% CI = -1.31,1.19; D-tDCS vs. C-tDCS SMD= 0.71, 95% CI = -1.11,2.53; D-tDCS vs. A-tDCS SMD= 0.77, 95% CI = -0.84, 2.39). In addition, no evidence showed differences in communication ability (C-tDCS vs. S-tDCS SMD= 0.08 95% CI = -1.77, 1.92; A-tDCS vs. S-tDCS SMD= 1.23 95% CI = -1.89, 4.34; D-tDCS vs. S-tDCS SMD= 0.70; 95% CI = -1.93, 3.34; A-tDCS vs. C-tDCS SMD= 1.15 95% CI = -2.48, 4.77; D-tDCS vs. C-tDCS SMD= 0.62 95% CI = -2.59, 3.84; D-tDCS vs. A-tDCS SMD= -0.52 95% CI = -4.60, 3.56). CONCLUSION: It seems that tDCS has no long-term effects on post-stroke aphasia patients in naming nouns and communication in terms of the results of our network meta-analysis. However, the results should be interpreted with caution. In the future, more RCTs with long follow-up times should be included in the research to conduct subgroup or meta-regression analyses to obtain a sufficient effect size.