Transcranial magnetic stimulation (TMS)
WHAT IS NEURONAVIGATION?
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What is TMS?
Repetitive transcranial magnetic stimulation (rTMS) is the delivery of intense magnetic pulses (like for an MRI) with the help of a powerful electromagnet (the coil) placed at the surface of the skull. The exact positioning of the coil is determined with a device called a neuronavigator and an MRI of the patient’s brain. The MRI is not essential, even if it greatly improves the accuracy of the positioning of the coil.
The dynamic magnetic field produces a weak electrical current through an electromagnetic induction mechanism, which is imperceptible to the patient in the precise zones and circuits of the brain involved in depression or other psychological and neurological illnesses. The level of activity of the cells in the brain is modified and can be increased or reduced. TMS causes an increase in blood flow, glucose metabolism and the concentration of certain neurotransmitters (GABA, glutamate, dopamine…).
The most frequent location of the coil for the treatment for depression is the left or right dorsolateral prefrontal cortex. Patient characteristics determine the zone and parameters of the treatment.
TMS does not require anaesthesia and is not painful. At most, some mild headaches can occur that respond well to standard painkillers.
TMS is a method of treatment as well as a diagnostic tool for some diseases like neurological conditions.
Who can benefit from TMS?
TMS is indicated for the treatment of depression in patients of all ages who have not benefitted from common antidepressant therapies or who show sensitivity to or cannot tolerate the side effects of medication.
TMS also shows encouraging results in the treatment of addictions (for example to cocaine), certain types of schizophrenia (symptoms of auditory verbal hallucinations, negative symptoms), fibromyalgia, chronic pain, tinnitus and rehabilitation after a stroke.
Is TMS effective?
TMS has been reported to be effective particularly in the treatment of depression in many cases (over forty studies) where previous treatment had not been successful.
One out of two patients receiving TMS reported a 50% decrease in intensity of symptoms and one out of three, complete remission (all symptoms absent) after six weeks of therapy.
Electroconvulsive therapy (ECT) continues to be more effective against depression but it is cumbersome because it requires general anaesthesia at every session and has more side effects than TMS.
TMS has been approved by health authorities in several countries, including the United States and the United Kingdom as a therapy for treatment-resistant depression.
How is the treatment performed?
The patient is seated comfortably in an armchair. Care is taken to remove all metal objects because they are sensitive to magnetic waves (jewellery, credit cards…).
Adhesive marks are placed on the head of the patient and the neuronavigator is used to obtain the optimal position for the magnetic coil. Since magnetic pulses are quite loud, ear protectors are provided.
The “motor threshold” of the patient is determined by a procedure at the start of the first session and on occasion afterwards in order to customise the intensity of the treatment and to determine the optimal energy level required.
The coil is then placed on the target area and treatment starts. In depression therapy, repeated pulse cycles lasting a few seconds are alternated with rest intervals. The duration of the whole treatment can vary, but the most frequent protocol used for depression lasts about 40 minutes. During the therapy, the patient hears a series of noisy “clicks” corresponding to the pulses and feels a tapping on the surface of the skull.
A daily session is required over at least two weeks, five days a week. Four to six weeks are usually needed for the maximum benefit. Afterwards, maintenance sessions, at less frequent intervals, can be advised if necessary.
The first session is always carried out by a medical doctor. Subsequent sessions can be undertaken by a health care specialist trained in TMS.
What are the side effects?
TMS does not have any of the side effects that are usually associated with antidepressants (weight gain, sexual dysfunction, gastric disorders, drowsiness or insomnia, dry mouth, sweating, etc.). It does not cause memory or attention deficit disorders.
The most common side effect reported, in about 10% of cases, is a mild headache or some discomfort during the therapy resulting from the magnetic impulses. These can easily be taken care of with standard analgesics (paracetamol for example). Most of the time, side effects are of light to moderate intensity and diminish over the sessions. It is extremely rare for patients to stop treatment on account of the side effects.
What are the risks and contraindications?
Like MRI, TMS uses a strong magnetic field and therefore cannot be used when there are any metallic devices inside the skull or within 30 cm of the stimulation area (with the exception of dental crowns and fillings). If these precautions are not followed, the metal element may heat, move or degrade, cause injury or even be fatal.
The following preclude treatment by TMS (non-exhaustive list):
– Aneurysm clips
– Implanted brain stimulation devices
– Electrodes for monitoring brain activity
– Metallic implants in ears or eyes
– Bullet fragments or shrapnel inside or near the head
– Face tattoos with metal or ferromagnetic ink
– Pacemakers or implanted defibrillators (in some cases)
The main risk, which is extremely low (0.1% of patients), is an epileptic seizure but this is considerably lessened by scrupulous observation of the recommendations for safety and by using customised stimulation parameters.
Is TMS reimbursed by insurance?
Repetitive transcranial magnetic stimulation, especially with neuronavigation, is still very new in Switzerland as a therapy for the treatment of depression, unlike in the United States and the United Kingdom. TMS is currently not reimbursed by either basic or complimentary insurances schemes. The sessions are therefore paid for entirely by the patient.
More information about costs and payment terms is available upon req
TMS is a treatment that targets a specific zone. Measurements of the surface of the skull of the patient for TMS treatment are generally taken with a measuring tape and are relatively accurate but not as precise as those obtained with neuronavigation.
The neuronavigator is a device equipped with special infrared cameras. Data from the MRI of the patient’s brain is entered. If no MRI is available, external points of reference of the skull are used for modelling. The device positions the magnetic field with accuracy to the millimetre exactly on the zone in the patient’s brain where treatment should be given and maintains the same accuracy from one session to the next.
The probability that the stimulus is delivered to the target area is thus much higher and the treatment likely to be more effective.
The Centre for Interventional Psychiatry is the first private medical practice in Switzerland which uses a neuronavigation system for transcranial magnetic stimulation.
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