Optimized transcranial direct current stimulation for post-stroke dysphagia with small electrodes: a double-blind, randomized, feasibility study protocol.

Rationale: Dysphagia affects approximately 78% of post-stroke patients. Transcranial direct current stimulation (tDCS) has demonstrated potential for the treatment of this condition. However, its effectiveness is influenced by individual brain anatomical structure. Also, small-sized electrodes offer significant advantages over conventional larger electrodes by providing increased focality of the electrical field, allowing for precise targeting of cortical regions. Studies that consider both factors are necessary to understand the tDCS effects on this population. Aims: The present study aims to assess the safety and feasibility of using focalized, optimized tDCS electrode montages in post-stroke dysphagia while considering individual brain anatomy variables improve swallowing function. Method and sample size estimates: The present study is set to recruit 30 participants, who will be randomly assigned into an active or sham group. Both groups will utilize optimized tDCS electrode positions, determined through computer modeling based on individual magnetic resonance imaging (MRI). Electrode positioning will be calculated to maximize the electric field (E-field) strength within the target region in the swallowing motor cortex, as designated by the investigator on the patient's MRI. The tDCS will be applied for 30 min at 2 mA for 20 sessions using sponge-coated disk electrodes (R = 1.5cm) designed to enhance focality. Study outcomes: The primary outcome measurements are the Functional Oral Intake Scale (FOIS) and the Penetration-aspiration Scale (PAS) together with various secondary outcomes, that include the Videofluoroscopic Dysphagia Scale (VDS) and other ancillary parameters that include voice quality and cough strength. Discussion: We hypothesize that the active tDCS group will demonstrate significant improvements in swallowing function compared to the sham group, establishing the feasibility of personalized, focal-electrode interventions for post-stroke dysphagia rehabilitation. Clinical trial registration: https://clinicaltrials.gov/ct2/show/NCT06305949, identifier: NCT06305949.