Cardiff University, Henry Wellcome Building, Heath Park, Cardiff
University of Oxford, Department of Psychiatry, Warneford Hospital, Oxford, and Andrew Duncan Clinic, Royal Edinburgh Hospital, Edinburgh
Andrew Duncan Clinic, Royal Edinburgh Hospital, Edinburgh
Whitchurch Hospital, Cardiff and Vale NHS Trust, Cardiff
Andrew Duncan Clinic, Royal Edinburgh Hospital, Edinburgh
University of Stirling Department of Psychology, Stirling
Neurostimulation Research Laboratory, Department of Psychiatry, University of Texas Southwestern Medical Center at Dallas, Texas, USA
Division of Brain Stimulation and Therapeutic Modulation, Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York State Psychiatric Institute, New York, USA
Correspondence: Professor Klaus P. Ebmeier, University of Oxford, Section of Old Age Psychiatry, Warneford Hospital, Oxford OX3 7JX, UK. Email: klaus.ebmeier{at}psych.ox.ac.uk
None. Funding detailed in Acknowledgements.
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Magnetic seizure therapy, in which seizures are elicited with a high-frequency magnetic field, is under development as a new treatment for major depressive disorder. Its use may be justified if it produces the antidepressant effects of electroconvulsive therapy (ECT), coupled with limited cognitive side-effects.
Aims
To evaluate the usefulness of a new 100 Hz magnetic seizure therapy device.
Method
We induced seizures with 100 Hz magnetic transcranial stimulation in 11 patients with major depressive disorder during one session of a regular course of ECT. Recovery times after seizures induced by magnetic seizure therapy and ECT were compared.
Results
Seizures could be elicited in 10 of the 11 patients. Stimulation over the vertex produced tonic–clonic activity on 9 out of 11 occasions. Stimulation over the prefrontal midpoint elicited seizures on 3 out of 7 occasions.
The mean duration of magnetically induced seizures was 31.3 s, ranging from 10 to 86 s. All patients had an exceptionally quick recovery of orientation: mean of 7 min 12 s (s.d.=2 min 7 s, range 4 min 20 s to 9 min 41 s). The recovery times were on average 15 min 35 s shorter with magnetic seizure therapy than with ECT in the same patients (paired-samples t-test: P<0.0001). Patients reported feeling less confused after magnetic seizure therapy. Side-effects were confined to myoclonic movements, associated with the use of etomidate.
Conclusions
The new 100 Hz magnetic stimulator elicits seizures in the majority of patients when administered over the vertex. Magnetic seizure therapy was associated with shorter recovery times and less confusion following treatment. Subsequent work will be required to assess the safety and effectiveness of magnetic seizure therapy in the treatment of depression.
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These early trials were a proof of the principle that magnetic seizure therapy could induce therapeutic seizures in a clinical setting, but they also indicated the need for improved magnetic seizure therapy devices (as discussed by Lisanby & Peterchev).16 A new prototype device (Magstim Company Ltd, Whitland, Carmarthenshire, Wales) capable of stimulating continuously at 100 Hz at maximum stimulator output (1.2 T at the coil surface) for up to 10 s became available for animal use in 2004. This device was used for the first time in 2004 in a study of rhesus monkeys.16 Since then, 275 magnetic seizure therapy sessions have been successfully performed in 11 rhesus monkeys. Seizures have been induced in all sessions and 100 Hz magnetic seizure therapy still demonstrates fewer cognitive side-effects in the monkey model than conventional ECT.17 A version of the 100 Hz magnetic seizure therapy device designed specifically for human use (the Magstim Theta; Magstim Company Ltd, Whitland, Carmarthenshire, Wales) became available in the middle of 2006. The current study was designed as a pilot to examine the feasibility of magnetic seizure therapy at 100 Hz in patients, its safety and side-effects, and recovery times compared with ECT.
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View this table: [in a new window] | Table 1 Treatment settings, duration of seizures and recovery of orientation during ECT and magnetic seizure therapy |
Magnetic seizure therapy
We used two custom-built Magstim Theta devices (Magstim Ltd, Whitland,
Carmarthenshire, Wales). This stimulator is capable of producing 100 Hz
magnetic stimuli at 1.2 T (at the centre of the coil) with a biphasic waveform
with a pulse width of 340–400 µs for up to 10 s duration (i.e. a
maximum of 1000 pulses). We used a round coil with an 80 mm average diameter
(47 mm inside diameter, 115 mm outside diameter). For positioning of the coil
we used standard 10–20 electroencephalogram (EEG) positions. The middle
of the coil was applied firmly to the head of the patients, and positioned
over Cz for vertical and Fz for frontal stimulation for
up to 10 s. The direction of current induced in the brain was
counter-clockwise. The inside of the coils heats from 20°C to 130°C
after 1000 pulses at 100% output stimulation; therefore, coils were cooled
down to 5–10°C in a refrigerator prior to stimulation and were
changed if a patient required restimulation. All treatments were given at 100
Hz frequency and at maximum stimulator output. When a patient was
restimulated, we allowed at least 20 s between stimulations. Staff and
patients wore ear protectors during magnetic seizure therapy.
Anaesthesia
For anaesthesia we used intravenous etomidate (0.15–0.3 mg/kg) as it
does not cause an increase in the seizure threshold and might even reduce
it.19 Muscle
relaxation was achieved with intravenous succinylcholine; since patients
recover more quickly from magnetic seizure therapy the dose was generally
lower than that routinely used in ECT (0.5–1.0
mg/kg).14
Seizure monitoring
Seizure duration during magnetic seizure therapy was measured from the
start of stimulation to the termination of the observed
seizure.12
Electroencephalogram seizure expression was monitored via bilateral
fronto-mastoid EEG using magnetic resonance image-compatible plastic
electrodes to prevent electrode heating during therapy.
Orientation assessment
Recovery of orientation after magnetic seizure therapy/ECT was assessed by
asking the patient for their name, date of birth, age, place and day of the
week. The point of orientation recovery was defined as the time when a patient
was able to recall four of these five items.
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Orientation was recovered after 4 min 36 s. Immediately upon awakening, the patient achieved a Mini-Mental State Examination20 score of 27/30 points. On the next day, the patients score was at the pre-ECT level of 30 points. A battery of further cognitive tests that included tests for verbal and visual memory, verbal fluency and executive speed was also administered and no relevant changes in performance from baseline were found (results not presented).
We have since treated 10 further patients. In order to explore optimal parameters of stimulation for this new procedure, we applied different numbers of pulses and changed the positioning of the coil between Cz and Fz. The results for each patient and the corresponding settings for their ECTs are presented in Table 1.
Seizures were elicited in 10 of the 11 patients. The one who did not fit was stimulated with only 600 pulses. Vertex stimulation appeared to be more effective in inducing seizure activity (Table 1; see patients 3, 4, 6 and 8). The mean duration of successful seizures was 31.3 s, range 9.5–86 s.
Orientation was recovered much faster after magnetic seizure therapy than after ECT. The mean time to recovery after successful seizures was 7 min 12 s (s.d.=2 min 7 s, range 4 min 20 s to 9 min 41 s). We compared these results with the recovery times of the same patients during their nearest ECT session(s) taking care that the order of ECT and magnetic seizure therapy sessions used for the calculation was approximately balanced. The mean recovery time after ECT was 26 min 35 s. When the recovery times of the nine patients who had both ECT and magnetic seizure therapy were compared in a paired-samples t-test, magnetic seizure therapy was shown to result in 15 min 35 s quicker recovery, and despite the small numbers, this result was highly significant at P<0.0001.
Patients uniformly commented that they felt less confused after magnetic seizure therapy. Side-effects of 100 Hz magnetic seizure therapy were restricted to the usual myotonic movements observed after etomidate anaesthesia. No serious immediate adverse events resulted from the use of magnetic seizure therapy.
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Position of stimulation coil
We also tested whether stimulation at 100 Hz was capable of inducing
seizures over the prefrontal cortex, which had been difficult to achieve at
lower
frequencies.9,12,13
We attempted seven prefrontal cortex stimulations in six patients. Of those,
three were successful (one at 500 and two at 1000 pulses) and four were not
successful (one at 500, one at 600, and two at 1000 pulses). Patients who did
not fit with prefrontal stimulation fitted when stimulated over the vertex
(Table 1). We conclude that
even at the maximum setting of the machine, some patients will only fit if the
coil is positioned over the vertex (i.e. closest to the motor cortex, which
has a lower seizure threshold than the prefrontal or precentral cortices).
Seizure duration and recovery
We measured seizure duration during magnetic seizure therapy starting from
the onset of stimulation. This is because we observed that the seizures in
magnetic seizure therapy start during the stimulation train. In contrast, in
ECT the convulsion typically does not start during electrical stimulation and
a latent phase is usually seen immediately after
stimulation.21
The mean duration of successful magnetic seizure therapy seizures was 31.3 s, range 10–86 s. Four patients had short seizures of 10, 18, 15 and 11 s (Table 1), which would not be considered therapeutic if evoked by ECT. Two of these patients were stimulated with only 600 pulses, raising the possibility that they may have had adequate seizures if stimulated at the maximum duration output (10 s) of the device.
In line with previous results,12 the recovery of orientation after magnetic seizure therapy was much faster than after ECT. Despite the small sample size, this difference was highly statistically significant and, more importantly, clinically meaningful. The ability to combine antidepressant efficacy with low neurocognitive adverse effects would be invaluable for patients who require neurostimulation therapies.22 All patients felt less confused after magnetic seizure therapy. Many patients felt as if they had received no treatment and remembered details of what had happened immediately prior to the therapy. For instance, patients were able to continue conversations after recovery that had begun just prior to therapy.
EEG changes during seizures
It has been noted that the EEG after magnetic seizure therapy differs
markedly from that after ECT, with a lower amplitude and relative absence of
post-ictal
suppression.12,14
We confirmed these differences after stimulation at 100 Hz.
Electroencephalogram traces during ECT showed high amplitude, synchronised EEG
activity and clear post-ictal suppression which were markedly different from
the EEG recorded after magnetic seizure therapy (traces available on request
from the authors). The observed differences between ECT and magnetic seizure
therapy ictal expression on EEG could be due to the more focal stimulation
achieved with magnetic seizure therapy, which spares deeper brain regions such
as the hippocampus that may be implicated in the cognitive side-effects of
ECT.6 Differences in
patterns of seizure expression might also explain the much faster recovery
after magnetic seizure therapy. Another explanation for differences in ictal
EEG expression between magnetic seizure therapy and ECT may stem from the fact
that we were not recording EEG from directly under the magnetic coil, where
the induced currents and seizure expression should be at its strongest.
Specifically, our scalp EEG recordings were collected from bilateral
prefrontal cortex, whereas the most effective coil placement was over the
vertex. We have since observed that placing the electrodes over the motor
cortex during magnetic seizure therapy produces clearer seizure activity,
confirming our impression that these seizures are more localised (S. H.
Lisanby, personal communication, 2008).
Outlook
Limitations of this work include the small sample size, open design and
non-randomised nature. Nevertheless, this initial pilot study found that
magnetic seizure therapy delivered with the new Magstim Theta device was
well-tolerated and reliably produced seizures in the majority of patients,
while resulting in much less post-ictal confusion. These encouraging initial
results beg the question of the efficacy of this new investigational
intervention for severe major depression. Previous open studies using 40 Hz
and 50 Hz magnetic seizure
therapy4,14
showed promising results, although magnetic seizure therapy did not reach the
effect size of optimal ECT. The ability to provide higher-dosage seizures
relative to seizure threshold may narrow the gap in efficacy. This will be
tested in the context of new trials now underway using the 100 Hz device to
assess the effectiveness and safety of high-dose magnetic seizure therapy
relative to ECT.
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Support for this work came from the Cardiff and Vale NHS Trust (to G.K., N.K. and M.A.) for the purchase of the Magstim Theta at Cardiff; and from a Trial Platform Grant of the UK Medical Research Council (G0401083) and the Gordon Small Charitable Trust (to K.P.E., R.E.OC and A.S.) for the magnetic seizure therapy trial in Edinburgh. The Magstim Company supported travel for S.H.L. and M.M.H. to attend the first magnetic seizure therapy treatments at Cardiff and Edinburgh. The development and preclinical testing of the prototype 100 Hz magnetic seizure therapy device were supported by a US National Institute of Health Grant (NIH R01 MH60884 to S.H.L.). S.H.L. and M.M.H. received a grant from the Stanley Medical Research Foundation for a randomised controlled trial of magnetic seizure therapy v. ECT. S.H.L. has also received grants to support magnetic seizure therapy development from National Alliance for Research on Schizophrenia and Depression, the American Federation for Aging Research, and New York State Foundation for Science, Technology and Innovation. For other work not the focus of this report, S.H.L. and M.M.H. have received funding from Neuronetics Inc. and Cyberonics Inc. Columbia University has submitted a patent on a novel transcranial magnetic stimulation technology developed in the laboratory of S.H.L. (not the topic of this report). None of the authors hold patents, office, or stock in magnetic seizure therapy or magnetic seizure therapy-related companies.
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