Predictors of response to synchronized transcranial magnetic stimulation for major depressive disorder

Background: Synchronized transcranial magnetic stimulation (sTMS) is a new modality to reduce symptoms of major depressive disorder (MDD). sTMS uses rotating neodymium magnets to deliver low-field stimulation matched to the individual alpha frequency (IAF). A previous multisite study showed that sTMS significantly reduced MDD symptoms in the per-protocol sample. To this end, we evaluated clinical features associated with optimal sTMS outcomes.

Methods: Using the per-protocol sample (n = 120) from the parent sham-controlled trial, we performed univariate and stepwise linear regression to identify predictors of response after 6 weeks of sTMS. A subsample (n = 83) that entered a 4-week open/active continuation phase also was examined. Candidate variables included age, sex, comorbid anxiety, number of failed antidepressants in the current depressive episode, MDD severity (17-item Hamilton Depression Rating Scale; HAMD17), anxiety symptom severity (HAMD17 anxiety/somatization factor), and IAF.

Results: We found that greater baseline depressive (p < 0.001) and anxiety (p < 0.001) symptom severity were associated with better response to active sTMS, whereas fewer failed antidepressant trials predicted superior response to sham (p < 0.001). MDD severity and antidepressant resistance predicted outcomes in open/active phase sTMS; lower IAF predicted poorer response in participants who received 10 weeks of active sTMS (p = 0.001).

Conclusions: Participants with greater severity of depression and higher anxiety had superior responses to active sTMS, whereas treatment naïve individuals exhibited a greater response to sham. These results lend support to the primary efficacy findings, and support further investigation of sTMS as a therapeutic noninvasive brain stimulation modality.