Abstract
OBJECTIVE: Major depressive disorder is heterogeneous. While transcranial direct current stimulation (tDCS) is an effective treatment, its impact on symptoms remains underexplored. This ancillary study investigated the effects of home-use tDCS on depression symptom clusters. METHODS: Data were used from the Portable Transcranial Electrical Stimulation and Internet-Based Behavioral Therapy for Major Depression Study (PSYLECT) study, in which 210 depressed patients were randomized to active (n=137) or sham tDCS (n=73) for 6 weeks. Items from the Hamilton Depression Rating Scale were grouped into symptom clusters using hierarchical clustering. Treatment effects were analyzed with mixed regressions. An alternative clustering solution was also evaluated using a larger sample. RESULTS: Four clusters were identified: emotional, sleep, psychomotor, and psychosomatic symptoms. None showed significant group differences (sleep: p = 0.058, Cohen's d = 0.36, emotional: p = 0.976, d = -0.01, psychosomatic: p = 0.157, d = 0.27, psychomotor: p = 0.944, d = 0.01). The alternative clustering solution produced a similar sleep cluster, where tDCS led to significant reductions (p = 0.033, d = 0.41), but no differences were observed in other clusters (emotional: p = 0.707, d = 0.07, atypical: p = 0.537, d = 0.12). CONCLUSION: The association between tDCS and sleep improvement warrants further study. tDCS may be more effective for specific symptom clusters.