Transcranial magnetic stimulation for pain control. Double-blind study of different frequencies against placebo, and correlation with motor cortex stimulation efficacy

To assess, using a double-blind procedure, the pain-relieving effects of rTMS against placebo, and their predictive value regarding the efficacy of implanted motor cortex stimulation (MCS). Three randomised, double-blinded, 25 min sessions of focal rTMS (1 Hz, 20 Hz and sham) were performed in 12 patients, at 2 weeks intervals. Effects on pain were estimated from daily scores across 5 days before, and 6 days after each session. Analgesic effects were correlated with those of subsequent implanted motor cortex stimulation (MCS). Immediately after the stimulating session, pain scores were similarly decreased by all rTMS modalities. Conversely, during the following week, 1 Hz stimulation provided significantly less analgesia than 20 Hz and placebo, and was pro-algesic in some patients. Placebo and 20 Hz rTMS were effective on different patients, and only 20 Hz rTMS predicted the efficacy of subsequent MCS, with no false positives. While 1 Hz rTMS should not be used with analgesic purposes, high-frequency rTMS may become useful to select candidates for MCS. Placebo effects are powerful and should be controlled for. Immediate results after a single rTMS session are misleading. Defining rTMS parameters is a crucial step before proposing rTMS as predictive test of SCM efficacy in clinical practice.