Transcranial Magnetic Stimulation (TMS) for Depression – Review of the Evidence

TMS involves placing a small coil near the scalp that when engaged generates a magnetic field that induces an electrical field in the brain’s outer cortex in regions that are close to the coil.

Over the last 20 years, a method called repetitive TMS (rTMS) has become widely used in clinical practice which occurs in a rhythmic and repetitive form. [3]

rTMS therapy is focused and so can be used to target discrete locations, such as the DLPFC, where it is typically used to deliver magnetic pulses at either a ‘high’ frequency of 10-20 Hertz or a ‘low’ frequency of ≤1 Hertz.

Low-frequency rTMS reduces neuronal excitability, whereas high-frequency rTMS increases cortical excitability.

The most common area targeted in depression is the DLPFC.

A large number (>40) independently conducted sham-controlled trials have evaluated the efficacy of TMS treatment of TRD. These studies have been summarised in multiple meta-analyses that have consistently supported the antidepressant efficacy of repetitive TMS (rTMS).

rTMS has also been evaluated in a number of larger multi-site trials. Several of these will be described in the following section:

Study One – Neuronetics Trial

A multisite study across 23 sites globally (which including our site in Melbourne, Australia) was the first multi-site study to analyse the clinical outcomes of TMS-mediated excitation of the DLPFC. [5]

It included 301 patients with MDD who were diagnosed with a moderate level of resistance to antidepressant medication.

Patients were randomly allocated to one of two groups where they received either TMS therapy or a placebo (sham coil). Treatment was daily and lasted between four and six weeks.

TMS stimulation was set at a frequency of 10-Hertz, which was pulsed for four seconds and had intervals of 26 seconds between pulses. This was repeated 75 times per daily session.

Patients who responded to treatment then had their TMS treatment tapered across three weeks, which was then followed by antidepressant monotherapy and observations over 6 months.

Researchers employed MADRS analysis to score effect of treatment, and this analysis showed that after the initial TMS treatment regime there was an effect size of 0.39.

The primary outcome analysis was not significant although significant benefits were seen on multiple other outcome measures.

There was also benefit shown for those individuals who had previously failed just one depression medication regimen, and this finding led to device approval in the US in late 2007.

Study Two – NIMH Trial

A second multi-site trial (government agency funded) across four sites in the US involved 190 patients who had been diagnosed with MDD and again showed a moderate level of resistance to depression medication. [6]

Patients were randomised to receive either daily TMS to the left DLPFC or placebo, for between 3 and 6 weeks determined by a response. Stimulation was set at a frequency of 10-Hertz with pulses lasting four seconds and intervals of 26 seconds between pulses. This regimen was repeated 75 times per daily session.

To determine the efficacy of TMS treatment, researchers used HAMD24 scoring. Data showed that active TMS was reported to produce a clinically meaningful remission rate that was 4.2 times greater than when using the sham coil.

However, in real numbers, only 15% of patients reached remission with 4% in the placebo group also reaching a similar remission status.

Study Three – Brainsway Trial

This more recent study was across 20 sites globally and included 181 patients with MDD who had previously failed to respond to at most four different antidepressant treatment trials. [7]

Patients were randomly grouped to receive TMS to the left DLPFC or placebo for 5 sessions per week for 4 weeks.

This study used a proprietary ‘deep’ TMS coil that penetrates more deeply but also produces wider cortical stimulation

Stimulation was set at a frequency of 18-Hertz with a pulse duration of two seconds and intervals of 20 seconds between pulses.

This was repeated 55 times per daily session. After four weeks, patients were given a maintenance phase of twice-weekly TMS therapy sessions for 12 weeks.

After 5 weeks of treatment, the change in HAMD21 scores showed an improvement of 6.39 for TMS versus a 3.11 improvement with placebo. The response to treatment rate was a statistically significant 38.4% of patients at week-5 and 44.3% of patients at week-12.

Remission from depressive symptoms was a statistically significant 32.6% of patients at week-5. However, the remission rate at week 12 was a non-significant 31.8% when compared to placebo.

One of the major questions posed by researchers and clinicians is whether TMS treatment has long-lasting effects once the patient has been tapered off of TMS therapy and has begun more traditional antidepressant medication.

In one study, 10 out of 99 patients relapsed within a mean time of 23.5 weeks as estimated using a Kaplan-Meier analysis. [8]

Furthermore, 38 patients had worse symptoms although 32 of the 38 re-achieved symptoms benefits after a second round of TMS in conjunction with an adjunct antidepressant.

After 6 months, 50 out of the 99 patients maintained a remission-free status based on patient analysis with MADRS and HAMD24 questionnaires. Also, the majority of the patients who received TMS were also shown to have achieved significant improvements in quality of life.

In a follow-up study of those patients that took part in the NIMH trial, 62% of 120 patients maintained remission free status 12 months after TMS therapy. [9]

Overall most studies have put the durability of TMS to treat depression between 64 – 90 % over a 3 to 12 month period after TMS.

TMS is seen as being a safe procedure however the possibility of a seizure during TMS therapy is a small yet significant safety concern. In a study of 325 patients with an accumulative 10,000 treatment sessions, no seizures were observed. [10]

The most common adverse events with rTMS are headaches and scalp discomfort. Discontinuation rates in clinical trials are usually well below that seen with medication. Switching is possible in patients with bipolar disorder.

Local and international experience has demonstrated that rTMS can safely be provided as an outpatient therapy with no restrictions required of the patient after attendance for treatment.

rTMS is now recommended in all relevant depression treatment guidelines as an approach that should be considered in the standard care of patients with depression.

A recent publication by Perera and colleagues in 2016 outlines the recommended clinical practice essentials for TMS. [11]

The following pre and post-treatment guidelines briefly summarise some of the information regarding good clinical practice.

Pre-Treatment Planning

Pre-treatment involves planning a treatment regime that will provide the symptomatic relief of MDD only in patients who have failed to achieve a satisfactory improvement after receiving antidepressant medication.

Alternatively, TMS therapy can also be applied to patients who have had TMS therapy previously and have either benefitted from treatment or are currently experiencing a recurrence of depressive symptoms.

Safety considerations should include analysis of the chance of a seizure with all staff and physicians ably trained to respond to such an event.

Furthermore, training is device specific and is a compulsory requirement for all staff as well as showing a complete understanding of device-specific standard operating procedures for administering TMS therapy.

Post-Treatment Planning

The cessation of rTMS treatment is likely to ideally involve the provision of a period of weaning off of therapy, usually with a decreasing schedule of sessions over a number of weeks.

Post-treatment planning after TMS therapy includes the requirement to evaluate how to minimise the risk of relapse in successfully treated patients.

This can include relevant antidepressant medication (and consideration of lithium) or additional TMS if depressive symptoms re-emerge. Evaluation should use relevant health questionnaires such as IDS-SRT and the BDI to determine what effect if any, TMS therapy had on depressive symptoms. Maintenance rTMS schedules do seem to have a meaningful benefit in reducing relapse.

Due to the resistant nature of depression, partial and non-responders are likely, and therefore non-responders may have treatment extended by 1-2 weeks.

An alternative approach in non-responders is to switch and conduct a trial of low-frequency stimulation applied to the right DLPFC, something that can be effective in a subgroup of patients.

Partial responders, on the other hand, may have their treatment extended beyond the initial 6 weeks if it is argued that they haven’t quite reached maximal benefit and will do so within 2 weeks.

rTMS treatment is currently being provided on both an inpatient and outpatient basis. Outpatient provision is considered safe and has the benefits of allowing slow weaning of therapy and reduced dislocation of patients from their home environment.

rTMS is an effective treatment for Major Depressive Disorder in people who have comorbid anxiety disorders. [Clarke E et al., 2019]

There is some debate as to the use of rTMS as a substitution treatment under the circumstances of ‘effective electroconvulsive therapy (ECT)’. [Malhi et al., 2019].

Two small case series [Cristancho et al., 2013] , [Noda et al., 2013] have found that rTMS may be successfully substituted (such that it maintains or improves clinical status) for maintenance ECT terminated due to tolerability issues.

Benzodiazepines are known to reduce response to rTMS while psychostimulants may enhance response. [Hunter et al., 2019]. The case to reduce benzodiazepines before rTMS is not clear. [Pridmore S, 2019]

In another small study, long-standing treatment-resistant depression patients underwent 3 sessions per week deep (d) TMS added to a previously failed SSRI. 35.3% of patients remitted after 4 weeks with just 12 dTMS sessions and no dropouts. The only side effect was a headache. [Tendler A et al., 2018]

According to the recent RANZCP guidelines,

The availability of rTMS should not interfere with the delivery of effective psychological and/or pharmacological treatment strategies and it should not delay the administration of ECT. [Malhi et al., 2021]

High Frequency vs Low-Frequency rTMS

LF-rTMS sessions are shorter, possibly better tolerated and with fewer side effects.

LF-rTMS to the right DLPFC is emerging as an even superior treatment alternative to HF-rTMS over the left DLPFC in MDD, particularly in bipolar patients with a higher anxiety degree. [Escribano B et al., 2019]

Systematic reviews and meta-analyses of sham-controlled studies of rTMS for depression show statistical superiority of active treatment over sham. However, the clinical significance of this difference has been questioned (Health Quality Ontario, 2016), and overall, greater efficacy is reported for high-frequency left DLPFC and low- frequency right DLPFC stimulation, and for longer treatment courses using higher numbers of stimuli per session. [RANZCP Guidelines, 2020]

rTMS plus Psychotherapy

A study of 196 patients combining rTMS and psychotherapy [Donse L et al., 2018] based on principles of cognitive-behavioural therapy for 10 sessions resulted in

• 66% response
• 56% remission rate at the end of the treatment
• 60% sustained remission at follow-up

Augmentation of rTMS with Behavioral Activation therapy shows promise. [Escribano B et al., 2019]

Augmentation of rTMS with antidepressants may help in the treatment of the acute phase and prevent relapse and recurrences. [Escribano B et al., 2019]

Predictors of response may be linked to illness characteristics, nature of depression and severity which is relevant to the use of rTMS in melancholic depression. [Trevizol A et al., 2020]

Positive predictors of response:

• Psychomotor retardation
• Younger patients with cognitive and affective symptoms (< 45 years)
• A low score of treatment resistance
• High levels of sleep disturbance
• Short duration of episode (<4 years)
• Employment
• Higher levels of extraversion

Negative predictors:

• Higher baseline severity of both depressive and anxiety symptoms was associated with a lower chance of achieving remission
• Feelings of guilt
• Depressed mood
• Somatic symptoms
• Greater number of treatment failures
• Non-response to ECT [Kar S., 2019]
• Psychotic depression

A more recent systematic review and meta-analysis investigating the effects of rTMS on the left dorsolateral prefrontal cortex on neuropsychiatric symptoms presenting across diagnoses showed: [Kan et al., 2023]. 

Large effect size:

• Craving

Moderate effect Size:

• Depressive symptoms

Small Effect Size: 

• Anxiety
• Obsessions or compulsions
• Pain
• Global cognition
• Declarative memory
• Working memory
• Cognitive control and;
• Motor coordination

Non-significant:

• Attention
• Suicidal ideation
• Language
• Walking ability
• Fatigue and;
• Sleep

TMS is a safe and effective computerised medical device that delivers non-invasive and focal magnetic stimulation to the DLPFC over a brief duration of time.

The pulsing magnetic fields induce electrical currents in these brain regions and over the course of 4 to 6 weeks can significantly increase a patient’s chances of achieving remission from depression.