Impact of two or less missing treatment sessions on tDCS clinical efficacy: results from a factorial, randomized,...

Transcranial direct current stimulation (tDCS) is a neuromodulatory intervention with recent clinical trials showing promising results in major depression treatment. Although tDCS has some appealing characteristics (e.g., low cost, ease of use, and relatively benign profile of adverse effects), one important drawback of the technique is the need to deliver consecutive, repeated sessions for several weekdays. However, no study investigated whether absences during this acute treatment phase impact on tDCS efficacy, and, if so, whether absences should be considered dropouts, therefore increasing attrition.

To examine this issue, we used data from a randomized, factorial, sham-controlled tDCS study that recruited 120 depressed patients. In this trial, the acute treatment phase consisted of ten consecutive sessions delivered once daily from Monday to Friday; two nonconsecutive missed visits were allowed, with extra tDCS sessions being performed to complete the original number of sessions.

Our main finding was that the procedure of granting one to two absences during the acute treatment phase did not impact on tDCS antidepressant efficacy. Moreover, out of 103 completers, only 41 (39.8%) patients presented no missing visits and 25 (24.3%) presented two absences. These patients did not differ in clinical and demographic characteristics; thus, absences were probably circumstantial (e.g., traffic congestion, personal obligations).

Absences during the acute tDCS treatment phase are common, which support the use of flexible schedules in future tDCS trials as to minimize attrition. Also, further studies should access whether higher number of absences can compromise optimal tDCS efficacy.