Effects of home-use transcranial direct current stimulation on clusters of depressive symptoms: an ancillary analysis of the PSYLECT study.

Objective: Major depressive disorder (MDD) is heterogeneous. While transcranial direct current stimulation (tDCS) is an effective treatment, its impact on symptoms remains underexplored. This ancillary study investigated home-use tDCS effects on depression symptom clusters.

Methods: Data were from the Psylect study, where 210 depressed patients were randomized to active (n = 137) or sham tDCS (n = 73) for six 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, established with a bigger sample, was also evaluated.

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), while other clusters exhibited no differences (emotional: P = 0.707, d = 0.07, atypical: p = 0.537, d = 0.12).

Conclusions: Associations of tDCS with sleep improvements warrant further study. tDCS may be more effective for specific symptom clusters.