BRAIN STIMULATION: Basic, Translational, and Clinical Research in Neuromodulation
Volume 2, Issue 3 , Pages 163-167, July 2009

The effect of daily prefrontal repetitive transcranial magnetic stimulation over several weeks on resting motor threshold

  • Paul Zarkowski, MD

      Affiliations

    • University of Washington, Seattle, Washington
    • Corresponding Author InformationCorrespondence: Dr. Paul Zarkowski, 325 Ninth Ave, Box 359895, Seattle WA, 98104-2499.
    • ,
  • Rita Navarro, MD

      Affiliations

    • University of Washington, Seattle, Washington
    • ,
  • Martina Pavlicova, PhD

      Affiliations

    • Columbia University, New York, New York
    • ,
  • Mark S. George, MD

      Affiliations

    • Brain Stimulation Laboratory, Medical University of South Carolina, Charleston, South Carolina
    • ,
  • David Avery, MD

      Affiliations

    • University of Washington, Seattle, Washington

Received 24 July 2008; received in revised form 21 January 2009; accepted 4 February 2009. published online 06 April 2009.

Background

The resting motor threshold (rMT) is an important factor in the selection of treatment intensity for patients receiving repetitive transcranial magnetic stimulation (rTMS). In many clinical studies to date, because of the concerns about potential drift, the rMT has been routinely remeasured weekly or every fifth session.

Objective

Our aim is to investigate whether ongoing treatment with rTMS affects the rMT, the degree of change, and whether frequent remeasurement is needed.

Methods

Clinical data were drawn from 50 medication-free patients who were receiving treatment for major depression with rTMS in a large US National Institutes of Health (NIH)-sponsored multisite study. Four measurements of rMT were obtained, including before and after the double-blind phase, followed by weekly measurements during the open phase. Active treatment consisted of 75 four-second trains of 10-Hz stimulation applied over 37.5 minutes with the coil over the left dorsolateral prefrontal cortex (DLPFC) at 120% rMT.

Results

For the group as a whole, there was no significant change in the rMT during a minimum of 2 weeks of treatment with prefrontal rTMS (P = .911, 1-way analysis of variance). The average within-subject coefficient of variation was 6.58%. On average, the last rMT was 2.45% less than the baseline rMT (range: 32.3% increase, 40.6% decrease).

Conclusions

Daily left prefrontal rTMS over several weeks as delivered in this trial does not cause systematic changes in rMT. Although most subjects had less than 10% variance in rMT over time, five subjects had changes of approximately 20% from baseline, raising dosing and safety issues if undetected. We recommend that clinical trials of rTMS have periodic retesting of rMT, especially if the dose is at or near the edge of the TMS safety tables.

Keywords: rTMS, rMT, major depression, safety

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 The OPT-TMS study is supported by grants from the NIMH (5 R01 MH069887-04).

 Dr Avery currently receives funding from 5 R01 MH069887-04 and R21 AR053963-01. He has been a paid consultant to Northstar Neuroscience, Neuronetics, Inc, and Performance Plus. Dr Avery has received honorariums for speaking engagements from Eli Lilly and Takeda. For the past decade, his entire yearly compensation from all companies and speaking engagements is less than 5% of his university salary.

 Dr George currently receives funding from 5 R01 MH069887-04, 5 P20 DA022658-02, 1 R21 MH078046-01. He is a paid consultant to several device manufacturers, including Neuropace (DBS) and Cyberonics (VNS). He is an unpaid consultant to several TMS manufacturers (Neuronetics, Brainsway), and served as head of the DSMB for Aspect Medical. For the past decade, his entire yearly compensation from all manufacturers and speaking engagements is less than 20% of his university salary. He is the editor-in-chief of a new journal published by Elsevier, entitled Brain Stimulation and has written several books in this area. MUSC holds several patents in his name involving brain stimulation and imaging, one using fMRI (not EEG) to determine the best dose of VNS for a patient.

 Drs Zarkowski, Navarro, and Pavlicova have received funding from 5 R01 MH069887-04.

PII: S1935-861X(09)00008-4

doi:10.1016/j.brs.2009.02.001

BRAIN STIMULATION: Basic, Translational, and Clinical Research in Neuromodulation
Volume 2, Issue 3 , Pages 163-167, July 2009

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