Efficacy of Transcranial Direct Current Stimulation in Patients with Primary Progressive Aphasia: A Systematic Review...

Primary progressive aphasia (PPA) is a group of dementias characterized by progressive loss of specific language functions with relative sparing of other cognitive domains. Transcranial direct current stimulation (tDCS) has been introduced as a potential therapeutic option for PPA. We aim to evaluate the efficacy of tDCS in improving cognitive and language functions in patients with PPA.

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.

Our analysis encompassed ten RCTs comparing the efficacy of tDCS against sham treatment, with a total of 167 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 0.29, 95% CI 0.003-0.57, p = 0.05, I2 = 19%) and sustained benefits after two months or more (SMD 0.51, 95% CI 0.10-0.92, p = 0.01, I2 = 11%) in the untrained naming task. Similarly, for the trained naming tasks, significant improvement was observed (SMD 0.96; 95% CI 0.27 to 1.65; p < 0.01; I2 = 0%), even after the end of the tDCS treatment, with effects persisting for up to two months. (SMD 0.64; 95% CI 0.15 to 1.13; p = 0.01; I2 = 8%). However, no significant improvements were observed in cognitive tasks, untrained comprehension, language, and trained semantic tasks.

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.