Linguistic effects of transcranial Direct Current Stimulation (tDCS) in patients with primary progressive aphasia: A systematic review and meta-analysis of randomised controlled trials.

INTRODUCTION

Transcranial Direct Current Stimulation (tDCS) has shown promising language improvements in patients with primary progressive aphasia (PPA). Yet, individual studies have not been sufficient to yield strong conclusions on its efficacy.

METHODS

We performed a systematic review and meta-analysis of randomised controlled trials (RCTs) comparing tDCS against sham stimulation in patients with PPA. We searched PubMed, Embase, and Cochrane Central databases for eligible studies up to July 2024. Outcomes of interest included a performance in a range of language and cognitive tests. Summary data was extracted from published reports and pooled with a random-effects model using standardized mean differences (SMD) and 95 % confidence intervals (CI). The protocol was registered in PROSPERO, CRD42024499012.

RESULTS

We included 10 parallel and cross-over RCTs with 178 patients and 218 observations. tDCS yielded significant improvements for general naming (SMD 0.37; 95 % CI 0.07-0.67; p < 0.01) and spelling ability (SMD 0.65; 95 % CI 0.10-1.20; p = 0.02) There were no differences between groups regarding naming performance for trained (p = 0.76) and untrained items (p = 0.11), global language (p = 0.28), working memory (p = 0.15), semantic fluency (p = 0.38), and comprehension (p = 0.32).

CONCLUSION

In this systematic review and meta-analysis, tDCA showed benefits for performance in general naming ability and spelling in PPA patients. However, there was no significant evidence to supporting any effect of tDCS on other language functions.