Danielle de Sa Boasquevisque, MD
Trancranial direct current stimulation (tDCS) is a non-invasive neuromodulation therapy with the potential to enhance recovery after ischemic stroke. This technique uses a weak electrical current that ultimately leads to a polarity specific change in excitability: increasing cortical excitability (anodal tDCS), decreasing cortical excitability (cathodal tDCS), or a combination of both effects (bihemispheric). Many studies demonstrated benefit in chronic aphasia, but research within the early phase after stroke, when the mechanisms of neuroplasticity are more active, are still scarce.
In this article, the authors aimed to investigate the effects of online anodal tDCS applied over the left inferior frontal gyrus on aphasia recovery in the subacute phase after stroke. This study was a multi-center double-blinded clinical trial that enrolled patients with aphasia after ischemic or hemorrhagic stroke between 3 weeks and 3 months poststroke. Participants were randomized to 2 parallel groups: anodal tDCS (1mA, 20 minutes) and sham tDCS. They also received online tDCS while on 2 weeks (5 sessions/week) of 45-min word-finding language therapy session.
The primary outcome was the Boston Naming Test, and the secondary outcome included naming performance for trained/untrained picture item and verbal communication. Intention-to-treat analysis was performed. The authors included 58 participants (26 in the anodal tDCS group and 32 in the sham tDCS group). Baseline characteristics were not statistically different between the two groups, especially to what pertains to demographic variables and type and severity of aphasia.
In addition, the authors did not find any statistically significant differences between the active and sham groups for both the primary and the secondary outcomes, although it was noted that both groups improved markedly on the Boston Naming Test. No adverse effect was reported.
The limitations include, but are not limited to, the application of only one type of montage (anodal tDCS) and only one current intensity, and the lack of information about specific lesion topography.
In conclusion, there was no evidence that applying tDCS to enhance language recovery in aphasic patients during the early phase after stroke is beneficial. The spontaneous recovery seen in the subacute post-stroke period may have played a role in the negative findings of this study. A technique that shows positive results has to overcome the benefit of the natural history of stroke recovery, which has an ascending curve within 3 months.
For future studies, it will be worth addressing different types of montages since the “one site fit all” theory may not be true for neuromodulation therapy. Other parameters that influence different responses on tDCS therapy should be addressed (current intensity, length of treatment, lesion size/site). Using multimodal imaging (for example, Diffusion Tensor Imaging) as a surrogate marker of neurologic recovery should be an interesting approach for future research in early phase recovery after stroke.
