Shorter duration of depressive episode may predict response to repetitive transcranial magnetic stimulation

We investigated repetitive transcranial magnetic stimulation (rTMS) as a treatment for major depression. The experimental design comprised 15 medication-free subjects with major depressive disorder who were randomly assigned to receive 10 sessions of active or sham 10-Hz rTMS to the left dorsolateral prefrontal cortex at 110% motor threshold. Depression severity was measured by the Hamilton Depression Rating Scale (HDRS) and Beck Depression Inventory (BDI). Nonresponders to sham were allowed to receive active rTMS with the same parameters. Response to treatment was analyzed using a random regression model including episode duration and number of prior antidepressant treatments as covariates. Treatment (rTMS vs. sham) did not significantly predict changes in depression severity. Shorter duration of episode and more lifetime treatment trials significantly predicted improvements in BDI but not HDRS scores. Data from all subjects who received active rTMS (n = 14) showed that those with a depressive episode duration of shorter than 4 years had a mean HDRS decrease of 52% compared to 6% in those with an episode duration longer than 10 years. Active rTMS was well tolerated and was not associated with neuropsychological decrements when compared to sham. No significant antidepressant effects were found for 2 weeks of rTMS compared to sham. Among all subjects receiving rTMS those with a shorter duration of the current episode showed a greater response. Patients may need more than 10 treatments to obtain full benefit from rTMS. The design of future rTMS studies should consider these issues.