Slow Oscillatory Transcranial Direct Current Stimulation for Refractory Focal Epilepsy

tudy Design This was a prospective, open-label, single-arm pilot study conducted at the First Hospital of Hebei Medical University, China. Ten patients with refractory focal epilepsy (ILAE 2017 criteria) were enrolled. All patients completed the full treatment and follow-up protocol.

Participants Inclusion criteria: age 6-60 years, focal epilepsy, failed ≥2 anti-seizure medications, stable medication for ≥4 weeks, ≥2 seizures during 4-week baseline. Exclusion criteria: psychogenic nonepileptic seizures, progressive neurological disease, implanted electronic devices, pregnancy/lactation.

Intervention Slow-oscillatory tDCS (so-tDCS) was delivered using a constant-current stimulator (Hypnos Tech, China). The cathode was placed over the neuroimaging-defined epileptogenic zone (using MRI, FDG-PET, MEG, and scalp EEG). The reference anode was placed at FP1 or FP2 (contralateral). Stimulation parameters: 1 Hz sinusoidal oscillatory current, 2 mA peak-to-peak, delivered for 20 minutes per session, twice daily, with a 20-minute interval between sessions, for 14 consecutive days (total 40 minutes/day). Each session included a 20-second linear ramp-up and ramp-down. Sponge electrodes (13.68 cm²) soaked in 0.9% saline were used.

Outcome Measures Primary outcome: Percentage change in seizure frequency during treatment (14 days) and follow-up (8 weeks) compared with baseline.

Secondary outcomes: Change in interictal epileptiform discharges (IEDs) per hour on long-term EEG; change in alpha power (8-13 Hz) at Pz, CZ, P3, and C3 electrodes; safety and tolerability (adverse events); exploratory analysis of etiology (e.g., encephalomalacia vs. FCD) and treatment response.

Assessments Seizure diaries were kept daily. Long-term EEG (~16 hours) was recorded at baseline, post-treatment (week 2), and follow-up (week 10). Epileptiform discharges were quantified by two blinded electroencephalographers. EEG spectral analysis (FFT) was performed for theta, alpha, beta, and gamma bands.

Statistical Analysis Wilcoxon signed-rank test was used for seizure frequency changes. Repeated-measures ANOVA was used for IEDs. For alpha power, Wilcoxon signed-rank test with Bonferroni correction (12 electrode sites, α=0.00417) was applied. Effect sizes (Cliff's delta, Cohen's d) were calculated where appropriate. No imputation was made for missing data (none occurred).

Results Summary Seizure frequency significantly decreased during treatment (median reduction 95.65%, p=0.0020) and follow-up (median reduction 76.35%, p=0.0122). Six of ten patients achieved ≥78% reduction. IED frequency decreased significantly (p=0.0434). Alpha power increased significantly at Pz, CZ, and P3 (Bonferroni-corrected). The most pronounced seizure reduction occurred in the first week. No serious adverse events were reported; only mild transient skin itching/erythema in two adults, which resolved without treatment.

Limitations Small sample size, open-label design (no sham control), and heterogeneity in etiologies limit generalizability. The results are hypothesis-generating; sham-controlled randomized trials are needed to confirm efficacy.

Conclusion This pilot study provides preliminary evidence that so-tDCS is safe, well-tolerated, and associated with seizure reduction in refractory focal epilepsy, with a rapid onset and sustained effect. Further studies with sham control and larger cohorts are warranted.