Left handedness and response to repetitive transcranial magnetic stimulation in major depressive disorder

Objectives: Considerable research has demonstrated the efficacy of repetitive transcranial magnetic stimulation treatment (rTMS) in patients with major depressive disorder (MDD) with differences in effects related to laterality of stimulation. However, no systematic research has explored whether left-handed subjects respond in the same way as right-handed subjects. Methods: Data from 6 clinical trials (n = 310) were pooled and we explored whether left-handed patients with MDD responded in a similar manner to rTMS, including how they responded to both high-frequency left and low-frequency right-sided forms of treatment. Results: Overall, patients with MDD who were left-handed responded to a greater degree than right-handed patients to rTMS therapy. On subgroup analysis, notably limited by small numbers in the left handed groups, this effect was seen with high-frequency left-sided treatment but not with low-frequency right-sided treatment. The overall effect of a greater response in left-handed patients was not attributable to other clinical or study variables. Conclusions: Standard forms of rTMS treatment appear to be effective in patients with MDD who are left-handed and there seems no justification for modifying the laterality of treatment application in these patients.