Introduction: Primary Progressive Aphasia (PPA) presents a challenging decline in language function with limited treatment options. Emerging evidence suggests that transcranial direct current stimulation (tDCS) may offer targeted improvements in language abilities. This meta-analysis examines the impact of tDCS versus sham treatment in PPA patients, aiming to clarify its potential in enhancing language function and its limitations in broader cognitive outcomes.
Methods: PubMed, Embase, Cochrane Library, and Web of Science were searched up to June 2024 to identify randomized controlled studies (RCTs) comparing tDCS vs sham procedure in patients with PPA.
Results: Our analysis encompassed nine RCTs comparing the efficacy of tDCS against sham treatment, with a total of 146 participants. Due to the crossover design implemented in several studies, 94.5% of participants received active tDCS, while 91.1% received the sham intervention. The findings demonstrated significant improvements immediately post-tDCS (SMD 0.43, 95% CI 0.10; 0.76, p = 0.01) and sustained benefits after two months or more (SMD 0.51, 95% CI 0.10; 0.92, p = 0.01) in the untrained naming task. Similarly, for the trained naming tasks, significant improvement was observed more than one day after tDCS (SMD 1.04, 95% CI 0.28; 1.80, p < 0.01), which persisted up to two months (SMD 0.64, 95% CI 0.15; 1.13, p = 0.01). However, no significant improvements were observed in cognitive tasks, either immediately following tDCS (MD 0.27, 95% CI -0.48; 1.01, p = 0.40) or beyond one day but within two months (MD 1.81, 95% CI -1.18; 4.79, p = 0.24).
Conclusion : Our findings suggest that tDCS may be efficacious in augmenting naming tasks both acutely and over a prolonged period of up to two months. However, its effects on overall cognitive performance remain inconclusive. Further robust trials are warranted to elucidate its impact on cognitive function.
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