Impact of Transcranial Magnetic Stimulation on Functional Movement Disorders: Cortical Modulation or a Behavioral Effect?

Abstract

IntroductionRecent studies suggest that repeated transcranial magnetic stimulation (TMS) improves functional movement disorders (FMDs), but the underlying mechanisms are unclear. The objective was to determine whether the beneficial action of TMS in patients with FMDs is due to cortical neuromodulation or rather to a cognitive-behavioral effect.MethodConsecutive patients with FMDs underwent repeated low-frequency (0.25 Hz) magnetic stimulation over the cortex contralateral to the symptoms or over the spinal roots [root magnetic stimulation (RMS)] homolateral to the symptoms. The patients were randomized into two groups: group 1 received RMS on day 1 and TMS on day 2, while group 2 received the same treatments in reverse order. We blindly assessed the severity of movement disorders before and after each stimulation session.ResultsWe studied 33 patients with FMDs (dystonia, tremor, myoclonus, Parkinsonism, or stereotypies). The median symptom duration was 2.9 years. The magnetic stimulation sessions led to a significant improvement (>50%) in 22 patients (66%). We found no difference between TMS and RMS.ConclusionWe suggest that the therapeutic benefit of TMS in patients with FMDs is due more to a cognitive-behavioral effect than to cortical neuromodulation.

Repetitive transcranial magnetic stimulation for functional tremor: A randomized, double‐blind, controlled study

“…Our hypothesis predicted that if rTMS exerts its effect mainly through a cognitive-behavioral-suggestion mechanism, as previously argued, 17,22 we would not find any differences in outcome measures between the real rTMS and control groups. Moreover, given that there is no evidence that placebo interventions have a long-term benefit, any placebo-induced decrease in tremor would probably be transient, 23 as 42% and 57% of the patients included in the 2 consecutive studies by Garcin and colleagues 17,22 relapsed during follow-up. By contrast, any longer lasting changes induced by a real rTMS intervention applied with suitable parameters able to induce excitability changes would be prolonged by using hypnosis as an add-on therapy.…”

“…In all of these studies, TMS was instead used as a suggestive tool to induce a nonspecific cognitive-behavioral effect that was clearly demonstrated by Garcin and colleagues. 22 The benefit induced by the first intervention was maintained across the study's time course in almost all of the patients in the active group, whereas only 1 patient in the control group had an improved Tremor subscore at M12 when compared with baseline, and 2 of them had worse PMDRS or Tremor subscores at M6 and or M12 when compared with baseline. These poor M6 to M12 results for the control group were unexpected given the encouraging results described in previous uncontrolled studies using single suprathreshold rTMS sessions to improve FMD.…”

“…These TMS parameters were clearly not expected to cause long‐lasting cortical neuroplasticity changes. In all of these studies, TMS was instead used as a suggestive tool to induce a nonspecific cognitive‐behavioral effect that was clearly demonstrated by Garcin and colleagues …”

“…Their results do not, therefore, allow any firm conclusions to be drawn about the mechanism by which TMS may exert its potential therapeutic effect in FMD. Recently, Garcin and colleagues failed to find any significant differences between the therapeutic efficacy of one session of a magnetic spinal root stimulation and one session of a magnetic motor cortical stimulation in a large group of patients with mixed FMD. The authors concluded that in FMD, magnetic stimulation acts mainly through a cognitive–behavioral effect rather than by cortical neuromodulation.…”

Neurostimulation for Functional Neurological Disorder: Evaluating Longitudinal Neurophysiology

“…Proposed therapeutic mechanisms of neurostimulation for FND include neuromodulation, placebo, and cognitive behavioral effects . A recent study comparing cortical to spinal root stimulation favored the latter, but did not assess neurophysiological measures . Previous research has also shown that FND patients may have abnormal suppression of cortical excitability during movement imagination tasks .…”