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A case series of a novel 1 Hz right-sided dorsolateral prefrontal cortex rTMS protocol in
major depression
Jean-Philippe Miron 1,2,3,4,5,,*, Helena Voetterl 1,6,, Farrokh Mansouri 1,2,3, Daniel M. Blumberger
3,4,7, Zafiris J. Daskalakis 3,4,7 and Jonathan Downar 1,2,3,4.
1 Krembil Research Institute, University Health Network, Toronto, ON, Canada;
2 Poul Hansen Family Centre for Depression, University Health Network, Toronto, ON, Canada;
3 Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, ON, Canada;
4 Department of Psychiatry, Faculty of Medicine, University of Toronto, Toronto, ON, Canada;
5 Unité de Neuromodulation Psychiatrique (UNP), Centre Hospitalier de l’Université de Montréal
(CHUM), Université de Montréal, Montréal, QC, Canada;
6 Department of Cognitive Neuroscience, Maastricht University, Maastricht, Limburg,
Netherlands;
7 Temerty Centre for Therapeutic Brain Intervention at the Centre for Addiction and Mental
Health, Toronto, ON, Canada.
Equal authorship
* Corresponding author
Word count: 1003
Figures: 1
KEYWORDS: Treatment-Resistant Depression; TRD; Transcranial Magnetic Stimulation; TMS;
circular coil; DLPFC
To the Editor,
Although effective in treatment-resistant depression (TRD) and superior in tolerability to
medication, repetitive transcranial magnetic stimulation (rTMS) is currently burdened by high
costs of equipment acquisition, operation and technical complexity, precluding its widespread
use [1]. Simplifying the treatment technique could facilitate more widespread uptake of rTMS in
community settings. To this end, we investigated a non-cooled parabolic coil that is less
expensive than cooled figure of eight (Fo8) coils and allow simplified positioning because of its
central opening and wide stimulation area.
Between August 2018 and June 2019, 43 TRD patients completed at least fifteen (15)
sessions of 1 Hz right-sided dorsolateral prefrontal cortex (DLPFC) rTMS at our clinic using a
MagPro R30 and a MMC-140 parabolic coil (MagVenture, Farum, Denmark). Patient selection
process is described in our previous reports [2,3]. All patients provided informed consent and
this study was approved by the Research Ethics Board of the University Health Network.
Patients underwent once-daily right DLPFC-rTMS, with the center of the coil over F4
(calculated using a right-flipped adjusted BeamF3 algorithm [4]) for 15-30 sessions, 5
times/week (1 Hz, 60 s on and 30 s off, 6 trains, 8.5 min total stimulation time, 360 pulses/day
[5]), at 120% of resting motor threshold for the hand muscles. Patients completed a Beck
Depression Inventory - II (BDI-II) before every treatment session. Response was defined as an
improvement of ≥50% from baseline; remission was defined as a final treatment score ≤12 [6].
Overall, 43 patients underwent treatment (mean course length 22.4 ± 5.9 sessions) for a
total 979 sessions in this series. Regarding baseline characteristics, mean age was 40.6 ± 13.3,
with 63% female patients. Mean pre-treatment BDI-II was 36.4 ± 10.0. Number of previous
failed medication trials averaged 1.8 ± 1.5, and length of current episode 37.5 ± 54.9 months.
42 patients had a diagnosis of unipolar depression, 1 patient had bipolar depression and 20
(46.5 %) patients had a comorbid anxiety disorder.
No serious adverse events occurred. All patients experienced manageable pain levels,
with reported VAS scores ranging from 1 to 7 (VAS scale 1-10, 10 = maximum tolerable pain).
First-session mean pain rating was 6.5 ± 1.9, decreasing to 5.0 ± 2.4 by the final session. No
patient discontinued prematurely due to pain or any other adverse symptoms such as
headache, fatigue or vertigo. Mean motor threshold (MT) was 37.2 ± 9.0% of maximal stimulator
output. Average treatment intensity (120% of MT) was 44.1 ± 9.0%, with 2.3 ± 3.8 days to reach
target intensity.
Sixteen of the 43 patients (37.2%) achieved response (≥50% improvement from
baseline) and 10/43 (23.3%) achieved remission (mean improvement, 32.9% ± 31.8).
Responders showed steady improvement to maximal effect at their final week of treatment (Fig.
1A). An Epanechnikov kernel with band width of 15%, probability density estimate of the percent
improvement revealed a trimodal distribution of outcomes (Fig. 1B), with a notch near 50%
improvement, distinguishing a responsive subgroup (50 to 70%) from a non-responsive
subgroup (20 to 30%), similar to our previous reports [3]. Another notch around 0%
distinguished non-responders from a third group having experienced slight deterioration (-10 to
-20%) with treatment. Comparing deteriorating with non-deteriorating patients using
independent-samples t-test and logistic regression analysis wielded no statistically significant
differences (p < 0.05) in baseline characteristics (sex, age, comorbid anxiety, duration of the
depressive episode and number of medication). No association was also found between these
and response (p < 0.05).
To our knowledge, this is the first case series investigating the use of a parabolic coil
with 1 Hz stimulation in patients with MDD. The current results are superior to what was
reported in one of our recently published study [3] and in the classic and highly cited meta-
analysis of high-frequency (HF) rTMS by Berlim et al [7]. While encouraging, those results are
below what was reported in a large randomized controlled trial (RCT) by our group [8].
The main goal of this study was to test the use of this novel coil design. With
conventional Fo8 coils, targeting requires expertise, since scalp landmarks are hidden under the
coil. Due to its central opening, this coil allows for direct visualization of the landmarks, and
hence easier placement (Fig. 1C). This could potentially facilitate the delivery of rTMS in a wider
range of settings. The use of 1 Hz stimulation likewise facilitates more widespread use of rTMS
since it can be delivered on inexpensive stimulators.
Of note, the magnetic field is weaker in the central area of the parabolic coil, where the
opening is located (Fig. 1D). This raises the possibility that centering the coil over DLPFC could
in fact lead to less DLPFC stimulation and more stimulation of adjacent regions such as lateral
orbitofrontal cortex. Notably, stimulation of this area with rTMS [2] and intracortical electrodes
[9] has been shown to decrease depressive symptoms. Another study has also shown efficacy
of larger coils in TRD [10]. Placement of the parabolic coil more medially, to enhance
stimulation of DLPFC proper, may be worth future study.
An interesting and novel observation is the presence of patients who seem to have
experienced a deterioration in their mood with this protocol. This was not seen in previous
studies [2,3]. If replicated, this could warrant another study to determine if there are any
predictors of this trajectory of outcome.
Limitations of this case series include the use of only patient-rated scales, heterogeneity
of comorbidities and medications, and are similar to another case series from our group [3].
In summary, this series suggests that 1 Hz right DLPFC-rTMS delivered with parabolic
coils is safe, well tolerated, and effective in MDD patients with mild to moderate TRD. Although
the positioning of this coil might bear future optimization, the simplicity of the technique and its
applicability via low-cost equipment could greatly expand the reach of rTMS beyond specialized
centers in developed countries. Given the widespread global burden of MDD, more affordable,
scalable, and simplified rTMS techniques could markedly enhance the delivery and overall
impact of the technique on patient health around the world.
CONFLICTS OF INTEREST
HV and FM report no conflicts of interest. JPM reports research grants from the Brain &
Behavior Research Foundation NARSAD Young Investigator Award and salary support for his
graduate studies from the Branch Out Neurological Foundation. JD reports research grants from
CIHR, the National Institute of Mental Health, Brain Canada, the Canadian Biomarker
Integration Network in Depression, the Ontario Brain Institute, the Weston Foundation, the
Klarman Family Foundation, the Arrell Family Foundation, and the Buchan Family Foundation,
travel stipends from Lundbeck and ANT Neuro, in-kind equipment support for investigator-
initiated trials from MagVenture, and is an advisor for BrainCheck, TMS Neuro Solutions, and
Restorative Brain Clinics. DMB has received research support from the CIHR, NIH, Brain
Canada and the Temerty Family through the CAMH Foundation and the Campbell Research
Institute. He received research support and in-kind equipment support for an investigator-
initiated study from Brainsway Ltd., and he is the principal site investigator for three sponsor-
initiated studies for Brainsway Ltd. He received in-kind equipment support from Magventure for
investigator-initiated research. He received medication supplies for an investigator-initiated trial
from Indivior. He has participated in an advisory board for Janssen. In the last 5 years, ZJD has
received research and equipment in-kind support for an investigator-initiated study through
Brainsway Inc and Magventure Inc. His work was supported by the Ontario Mental Health
Foundation (OMHF), the Canadian Institutes of Health Research (CIHR), the National Institutes
of Mental Health (NIMH) and the Temerty Family and Grant Family and through the Centre for
Addiction and Mental Health (CAMH) Foundation and the Campbell Institute.
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