Determinants of adherence and safety in fully autonomous home-based transcranial direct current stimulation for fibromyalgia

Background Autonomous home-based transcranial direct current stimulation (HB-tDCS) is a scalable non-pharmacological intervention for chronic pain, but evidence under fully autonomous use remains limited. Objectives To identify factors associated with adherence to fully autonomous HB-tDCS; to characterize the incidence, severity, and timing of adverse events under active and sham stimulation; and to examine if patient and clinical factors, including adverse events and clinical response, are associated with variability in adherence and safety outcomes. Design Secondary pooled analysis of three double blind, sham-controlled randomized clinical trials. Subjects A total of 234 women with fibromyalgia diagnosed according to the 2016 American College of Rheumatology criteria. Methods Participants received a standardized autonomous HB-tDCS protocol (≥20 sessions). The primary outcomes were adherence and safety. We examined associations with adherence and adverse events using generalized linear mixed-effects models, adjusted for demographic, clinical, and psychosocial factors. We also explored whether the burden of adverse events explained the link between treatment allocation and adherence. Results Overall adherence was 82.6% (95% CI, 81.6–83.6). Adherence rates were similar for the active (84.7%, 95% CI, 83.3–86.0) and sham groups (80.5%, 95% CI, 78.9–82.1). Older age ( β = −0.024 sessions/year; 95% CI, −0.040 to −0.008) and greater central sensitization ( β = −0.025 per point; 95% CI, −0.040 to −0.010) were associated with lower adherence. Higher depressive symptom severity was linked to higher adherence ( β = 0.041 per point; 95% CI, 0.040–0.060). Most participants reported no adverse events (67.0%, 95% CI, 61.0–73.0), with no group differences ( χ 2 = 0.04, p = 0.83). Reported events were mostly mild and brief. Active stimulation led to more frequent tingling and erythema. Higher education ( β = 0.078; 95% CI, 0.023–0.130) and depressive symptoms ( β = 0.037; 95% CI, 0.020–0.050) were associated with more adverse event reports. Greater functional impairment was linked to fewer reported events ( β = −0.003; 95% CI, −0.040 to −0.007). Conclusions Autonomous home-based transcranial direct current stimulation was feasible, safe, and highly adhered to in fibromyalgia, with adherence and safety influenced by clinical and psychosocial factors, supporting scalable implementation in chronic pain.