Study design

We planned a double-blind, randomized, prospective, controlled study. A total of 80 MS patients with CI will be recruited.

Participants

Participants will be recruited from the outpatient services of the Department of Neurology, ASL3 Genoa, the AISM Liguria Rehabilitation Service, and the Neurorehabilitation Unit of IRCCS Ospedale Policlinico San Martino, Genoa. Inclusion criteria are: (1) diagnosis of MS according to McDonald’s criteria [16]; (2) age between 18 and 60 years (to minimize potential age-related CI); and (3) Expanded Disability Status Scale (EDSS) score ≤7.5 [17]. Exclusion criteria include major psychiatric disorders, epilepsy, previous brain surgery, MS relapse requiring steroid therapy within the past two months, and bilateral visual acuity <6/10.

Outcome measures

Cognitive status will be assessed using the Brief International Cognitive Assessment for MS (BICAMS) and the Paced Auditory Serial Addition Test (PASAT) with 3- and 2-second intervals. The BICAMS battery includes the Symbol Digit Modalities Test (SDMT), the California Verbal Learning Test, 2nd edition (CVLT-II), and the Brief Visuospatial Memory Test-Revised (BVMT-R). All instruments are widely used in cognitive assessment of PwMS. Patients scoring below the 5th percentile of age-, sex-, and education-adjusted norms in at least two of these tests will be eligible. Additional secondary outcomes will include self-reported measures of mood, fatigue, and quality of life: Multiple Sclerosis Quality of Life (MSQoL) [18], Beck Depression Inventory (BDI) [19], and Fatigue Severity Scale (FSS).

Methodology

Participants will be randomized into two groups: 40 in the experimental group (EG) and 40 in the control group (CG), matched for demographic characteristics (sex, age), EDSS score, and disease duration. All participants will undergo cognitive training using the Neurotablet system, a virtual-reality–based platform incorporating exergames for motor and cognitive rehabilitation. The system includes exercises with adjustable difficulty levels, enabling tailored treatment plans based on individual disability. The rehabilitation program will consist of 10 sessions (1 hour each), delivered 5 days per week for 2 consecutive weeks.

Intervention treatment

In addition to exergame training, EG participants will receive A-tDCS over the DLPFC, while CG participants will receive sham stimulation (S-tDCS) at the same site. Stimulation will be delivered using a battery-driven constant current stimulator with an LCD touchscreen (HDC progr), a portable stimulator (HDC stim), two cellulose sponge electrodes (7 × 5 cm) in saline bags, and conductive silicone electrodes. The anodal electrode will be placed over the left DLPFC (Brodmann area 46) using a positioning cap, and the reference electrode over the right shoulder. The DLPFC was chosen based on its established role in top-down cognitive control [20], conflict monitoring through anterior cingulate cortex connections [21], and evidence of improved working memory and executive function after A-tDCS in both healthy subjects [22] and PwMS [23]. Conductive gel will be applied under the electrodes to minimize impedance, which will be maintained below 5 kΩ. Only the tDCS operators will know the stimulation condition; participants and neuropsychological assessors will remain blinded. During each exergame session, A-tDCS will be applied online (concurrent with training) at 1.5 mA for 20 minutes, with a current density of 0.06 mA/cm², within established safety limits [4].

Placebo treatment

In the sham condition, stimulation will be delivered for 30 seconds at the beginning and end of each 20-minute session, producing the typical tingling sensation under the electrodes while preventing sustained cortical modulation. This procedure makes sham indistinguishable from active stimulation, ensuring participant blinding.

Timeline

Outcome measures will be administered at baseline, after the 10 treatment sessions, and at 1-month and 6-month follow-ups. The study duration is estimated at 2 years (Fig 1).

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Fig 1. Participant timeline according to the SPIRIT 2025 guidelines.

https://doi.org/10.1371/journal.pone.0337405.g001

The schedule displays enrollment, randomization, interventions (A-tDCS + exergames; sham tDCS + exergames), and timing of cognitive and secondary outcome assessments at baseline, end of treatment, 1-month, and 6-month follow-ups. Figure adapted from Chan et al., BMJ 2025 (Creative Commons Attribution License).

Patient enrollment began in September 2024 and is expected to be completed by January 2026. Data collection should be finalized by July 2026, and data analysis is anticipated to be completed by September 2026.

Statistical analysis and sample size

Descriptive characteristics of the included patients will be presented as mean ± standard deviation (SD) or median and interquartile range (IQR) for continuous variables and as absolute frequencies and percentages for categorical variables. Baseline characteristics of the patients will be also shown splitting the patients into the two groups of treatments and comparisons will be performed using Chi-squared test of Fisher’s exact test (for categorical variables) and Mann-Whitney U test or t-test (for continuous variables). Results of the SDMT and PASAT tests will be presented over time as Mean ± SD by showing separately the two groups of treatment. The repeated measures ANOVA will be used to assess the effect of treatment, the effect of time, and the interaction effect between time and treatment on the performance of the SDMT and PASAT tests. The sample size was calculated fixing a power of 0.80 and a significance level of 0.05 and we calculated the sample sizes required for between effect, for within effect and for the between–within interaction effects for both the neuropsychological tests, planning of picking as our final sample size the largest one. To calculate sample sizes, means of measurements over time and covariance matrix for the repeated measures were defined for the SDMT and PASAT tests based on clinical expectations and on previous findings [24]. The largest sample size was the one required for the between effect in the analysis of PASAT test, leading to a sample size of 33 patients in each group to detect the treatment effect of magnitude δ = 0.35. This sample size is even more satisfactory for the SDMT test, where a smaller sample size was required. However, assuming a drop-out rate of 20%, we finally need to enroll in 80 subjects with 40 patients per treatment group. After performing the repeated measures ANOVA, in case of presence of differences, we also plan to compare means using paired t-test, adequately adjusting for multiple testing. In case of missing data over follow-up, a multiple imputation by chained equations approach will be used with 10 imputations. Additionally, we will also perform the same analyses, using complete data to check the robustness of the results. A p value less than 0.05 will be considered significant. All the analyses will be conducted with the Statistical Software Stata version 16.0 (Stata Corporation, College Station, TX, USA). Randomization will be performed using computer-generated random numbers.

Oversight and monitoring

The IRCCS Ospedale Policlinico San Martino, Genoa, will act as coordinating center, responsible for trial oversight, central randomization, data management, monitoring, and communications with the ethics committee and trial registry. Participants will be recruited at three sites (ASL3 Neurology Department, AISM Liguria Rehabilitation Service, and IRCCS Policlinico San Martino). Each site will have a principal investigator responsible for local conduct. A Steering Committee (PI, site PIs, statistician, data manager) will oversee scientific and operational aspects, including protocol amendments, recruitment, adherence, and data quality. Data will be entered into password-protected eCRFs stored on a secure institutional server, with anonymization, restricted access, and regular back-ups. Given the low-risk nature of the trial, no Data Monitoring Committee is planned; safety will be overseen by the PI and site PIs and reported to the ethics committee.

Participants will be withdrawn in case of intolerable adverse events, clinical worsening requiring treatment changes, participant request, or investigator decision for safety. Stimulation parameters will not be modified during the trial. Adherence will be promoted through flexible scheduling, continuous support, and the engaging use of exergames.

Unblinding is not anticipated but may be authorized by the PI in exceptional safety-related circumstances. In case of discontinuation or deviation, all scheduled outcome data (clinical, neuropsychological, and patient-reported) will continue to be collected and included in intention-to-treat analyses.

All adverse events (AEs), whether solicited or spontaneous, will be documented; minor AEs will be managed immediately, while serious/unexpected AEs will be reported promptly to the PI and ethics committee. Any important protocol modifications will be submitted for ethics approval and updated in the trial registry.

Personal data will be collected only for study purposes, stored securely, and anonymized for analysis/publication. The final dataset will be accessible to the PI and study team only; the sponsor has no restrictions on access. No specific ancillary or post-trial care is planned; clinical needs will be managed as per standard practice. Given the minimal risk profile of tDCS and exergames, no specific compensation beyond national regulations is planned.

Results will be disseminated via peer-reviewed journals, conference presentations, and trial registries. A lay summary of findings will be made available to participants upon request.

Assessment of capacity to provide consent

All participants will be adults (aged 18–60 years) with a diagnosis of multiple sclerosis but without clinical evidence of severe cognitive or psychiatric impairment preventing autonomous decision-making. Before enrollment, the investigator will ensure each participant’s capacity to provide informed consent through a brief clinical interview and review of recent neuropsychological evaluations. Only individuals who demonstrated adequate understanding of the study’s aims, procedures, and potential risks were included.

The informed consent process, including capacity assessment, was reviewed and approved by the Comitato Etico Regionale della Liguria (Ethics Committee approval No. 447/2023 – DB id 13376). As all participants were deemed capable of providing informed consent, no surrogate consent procedures were required.