Intensive Home-based Transcranial Direct Current Stimulation for Long COVID

The goal of this clinical trial is to learn if home-based transcranial direct current stimulation (tDCS) works to treat fatigue and other symptoms in adults with Long COVID. It will also learn about the safety and home adherence of this intervention. The main questions it aims to answer are: Does active tDCS lower fatigue severity (FAS score) compared to sham treatment? What are the effects of the treatment sequence on cognition, pain, anxiety, depression, and quality of life? Researchers will compare a sequence of active tDCS followed by sham tDCS to a sequence of sham tDCS followed by active tDCS in a crossover design to see if the intervention works. Participants will: Receive a tapered schedule of home-based tDCS over 3 weeks per intervention period (totaling 42 sessions per intervention, separated by a 4-week washout period) Complete symptom evaluations and cognitive/clinical tests at baseline, after Phase 1, and after Phase 2 Log their daily sessions to track home adherence and report any potential side effects

Participants were recruited from the specialised Long COVID Unit at Basurto University Hospital (Bilbao, Spain) Inclusion Criteria: * Met the World Health Organization clinical case definition for post-COVID-19 condition * Suffered severe fatigue (Fatigue Assessment Scale \[FAS\] score ≥42). Exclusion Criteria: Exclusion criteria included age younger than 18 years or older than 65, pregnancy, recent initiation or modification of antidepressant or analgesic treatments within the previous month, major neurological or systemic disorders potentially explaining the symptoms, active substance abuse, and contraindications to tDCS such as metallic cranial implants, cochlear implants, ventricular shunts, or cardiac pacemakers. Patients unable to correctly self-administer the intervention at home were also excluded.