Comparative benefits of transcranial direct current stimulation (TDCS) treatment in patients with mild/moderate vs. severe depression

Objective: Major depressive disorder (MDD) is a psychiatric condition with high prevalence and poor treatment outcomes. Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation method with pilot trials showing promising results; however, it is still unclear the profile of patients in which tDCS is better indicated. Therefore, the aim of this study is to compare tDCS efficacy according to depression severity. Method: Thirty-two hospitalized patients (24 women) aged 30-70; with MDD according to DSM-IV.TR criteria were included. Drug treatment was not changed during the study. Mood was evaluated using the Hamilton Depression Rating Scale (HDRS) and Beck Depression Inventory (BDI). Patients were divided into two groups according to MDD severity, as measured by BDI (mild/moderate vs. severe). Anodal tDCS was bilaterally delivered to the Dorsolateral Prefrontal Cortex (DLPFC), using a stimulating current of 2 mA intensity for 20 minutes, twice a day, for 5 days consecutively. Depression was measured at baseline and after 5 (Tl), 12 (T2) and 35 (T3) days from the start of tDCS treatment. Results: Treatment was well tolerated without side effects. tDCS was effective in ameliorating depressive symptoms, with a significant mean BDI reduction of 11.1 (p<0.01) and HDRS of 7.1 (p<0.01) after one month of treatment (T3). Our mixed ANOVA model also showed significant time, depression severity, and time vs. depression severity effects for BDI (F 1203 = 11.0, p<0.01) and HDRS (F 1193= 8.1, p<.01) scales, indicating a greater tDCS effect for severe MDD. Similar results were found when depression severity was managed as a continuous variable. We observed no gender differences in tDCS effects. Conclusions: tDCS is especially effective in patients with severe MDD, providing sustained antidepressant effects after one month of intervention. These initial findings suggest tDCS could target this subgroup of patients to maximize clinical efficacy.