RESUMEN
AIM: To compare the efficacy of 0, 5, and 20 sessions of transcranial direct current stimulation (tDCS) for reducing symptoms of autism spectrum disorder (ASD). METHOD: Thirty-six male children with ASD (mean age 2 years 3 months, SD 4 months, age range 1 years 6 months-2 years 11 months) were balanced and stratified by age, sex, and baseline severity of ASD, to: (1) a control group that received 20 sessions of sham tDCS; (2) a 5-session tDCS group (5-tDCS) that received 5 sessions of active tDCS followed by 15 sessions of sham tDCS; and (3) a 20-session tDCS group (20-tDCS) that received 20 sessions of active tDCS. All groups participated in the special school activity of Khon Kaen Special Education Center, Thailand. The primary outcome was autism severity as measured by the Childhood Autism Severity Scale. RESULTS: The 5-tDCS and 20-tDCS groups evidenced greater reductions in autism severity than the control group at days 5 and 14, and months 6 and 12. There were no significant differences in the outcome between the 5- and 20-tDCS groups at any time point. Within-group analysis showed clinically meaningful improvements starting at month 6 for the participants in the control group, and clinically meaningful improvements starting on day 5 in both active tDCS groups, all of which were maintained to month 12. INTERPRETATION: The 5- and 20-session tDCS seems to reduce autism severity faster than sham tDCS. These effects maintained at least for 1 year. WHAT THIS PAPER ADDS: Twenty sessions of transcranial direct current stimulation (tDCS) were not superior to five sessions. Sham tDCS with a special school activity can reduce autism severity starting at 6 months after treatment. The benefits observed for 5 and 20 sessions of tDCS last for at least 12 months.