Magnetic Seizure Therapy (MST)

Magnetic Seizure Therapy (MST)

Magnetic Seizure Therapy (MST)

Primer

Magnetic Seizure Therapy (MST) is a form of brain stimulation performed under general anesthesia, where electromagnetic induction to is used to induce an electric field in the brain strong enough to elicit a generalized tonic-clonic seizure. MST is currently an investigative therapy, and being explored as an alternative to ECT.

Mechanism of Action

MST consists of a neurostimulator and coil that is placed in direct contact with the skull (non-invasively). When an electrical current passes through the coil, this creates a strong focal magnetic field is generated (2 Tesla). This magnetic field crosses the skull to reach brain tissue, and induces an electrical current causing neuronal depolarization and triggering a generalized seizure.^[1]

Delivery Parameters

Most studies have used a coil placement at the vertex of the head with a frequency of stimulation of 100 Hz, pulse width of 0.2 to 0.4 ms, and stimulation duration of 10 seconds.
MST is given on a similar schedule as ECT, between 2 to 3 times per week, with a minimum of of 12 treatments for once course.

Effectiveness

Early studies comparing ECT with MST have found similar rates of improvement of major depressive disorder. There are no studies of depressive relapse following MST or of relapse prevention strategies using MST. As a result, MST continues to be recommended as an investigational treatment.^[2]
A recent randomized clinical trial found no significant difference in response or remission rates between MST and ultrabrief pulse right unilateral (RUL) ECT in the treatment of major depressive disorder.^[3]
- Note that this finding does not mean the two treatments are similar in efficacy.^[4]

Side Effects

MST has lower rates of headaches and muscle aches compared to ECT.
Early studies suggest that there is less impact on anterograde amnesia, retrograde amnesia, and reorientation time (the time it takes after the seizure and emergence from anaesthesia to be fully oriented to person, place, and time).^[5]

Comparison with Other Brain Stimulation Therapies

Depression

Neurostimulation in the Treatment of Major Depressive Disorder

Milev, R. V. et al. (2016). Canadian Network for Mood and Anxiety Treatments (CANMAT) 2016 clinical guidelines for the management of adults with major depressive disorder: section 4. Neurostimulation treatments. The Canadian Journal of Psychiatry, 61(9), 561-575.

Neurostimulation	Overall Recommendation	Acute Efficacy	Maintenance Efficacy	Safety and Tolerability
rTMS	• First line (for patients who have failed at least 1 antidepressant)	Level 1	Level 3	Level 1
ECT	• Second line • First line in some acute clinical situations	Level 1	Level 1	Level 1
tDCS	• Third line	Level 2	Level 3	Level 2
Vagal Nerve Stimulation (VNS)	• Third line	Level 3	Level 2	Level 2
DBS	• Investigational	Level 3	Level 3	Level 3
MST	• Investigational	Level 3	Not known	Level 3