Transcranial Magnetic Stimulation (TMS) is a novel procedure used to treat neurological and psychiatric pathologies. Dr. Lluch, a specialist in Clinical Neurophysiology, explains the benefits of this procedure.
How Transcranial Magnetic Stimulation (TMS) works
Transcranial Magnetic Stimulation is a neurostimulation and neuromodulation technique based on the principle of electromagnetic induction of an electric field in the brain. This field must be of sufficient magnitude and density to depolarize neurons. When pulses are applied repetitively, they can modulate excitability, increasing or decreasing it depending on the stimulation parameters (frequency and intensity), as well as the duration of the trains and the pause between them.
This has potential behavioral and therapeutic consequences. Repetitive Transcranial Magnetic Stimulation (TMS) may become a promising non-invasive treatment in a wide variety of neuropsychiatric disorders.
Utilization of Transcranial Magnetic Stimulation (TMS)
Among the psychiatric disorders of therapeutic application are depression, acute mania, bipolar or panic disorder, OCD, schizophrenia, catatonia and post-traumatic stress syndrome. Also neurological disorders such as Parkinson’s syndrome, dystonia, tics, tinnitus, spasticity, post stroke rehabilitation and pain, either neuropathic or migraine.
Numerous specialists in Clinical Neurophysiology offer this therapeutic alternative in several disorders and it has already been approved in some countries in the treatment of depression refractory to medication. It is reasonable to expect an increasing introduction of this technique in the coming years.
Side effects of Transcranial Magnetic Stimulation (TMS)
The safety of the technique is supported by numerous experts, who state that patients with a history of epileptic seizures or neurosurgical interventions should not undergo TMS. In addition to those who have implanted aneurysm clips or other metallic devices, a pacemaker or hearing aids. Or if you are at risk of being pregnant or at risk of becoming pregnant during the sessions, as well as suffering from serious heart or circulatory diseases.
However, the risk of epileptic seizures in healthy subjects is very low. Transient hearing problems are easily solved by placing ear plugs in the ears during the technique.
The most frequent side effects are vasovagal syncope due to the tension associated with the procedure. Some patients may also experience isolated discomfort in the form of a post-procedure headache without consequences. Discomfort during the test has been described if there are contractions of the facial musculature or neck pain due to the position maintained during the test if the duration is prolonged. Isolated cases of mania, psychotic outbreaks, anxiety, agitation, suicidal ideas and insomnia have been reported.
How does Transcranial Magnetic Stimulation (TMS) work?
TMS involves the production of a very brief electrical current. By passing through a small copper wire coil placed on the scalp, it generates a magnetic field of sufficient intensity to penetrate the skull and depolarize the neurons of the cortex located about two centimeters below. Unlike TEE (Transcranial Electrical Stimulation), it is a painless technique.
TMS can be applied by means of an isolated stimulus, by means of pairs of stimuli separated by a variable interval or in trains, in a repetitive manner. In the latter case, it can be done by isolated pulses at fast frequencies (when the stimulus frequency is more than 1 Hz) and at slow frequencies (when the frequency is 1 Hz or lower). Such classification is based on the different physiological effects and degree of risk associated with the different stimulations. In turn, the application can be performed on a regular basis or in patterns, which refers to the application of short periods of TMS at high frequency separated by intervals of no stimulation.
There is an infinite variety of combinations of such protocols and it is important to note that the effects and safety of such protocols may differ and small changes can have a profound impact.
Transcranial Magnetic Stimulation (TMS), step by step
The patient sits in a reclining chair. He/she will have previously read a questionnaire and signed a consent form indicating and accepting the possible side effects of the technique and stating that there are no contraindications. However, any metallic object in the vicinity of the coil application must be removed and earplugs are provided.
In the first session, the motor threshold should be evaluated, which will consist of the application of the coil at initially subthreshold intensities, which will increase until the motor contraction of the right tenar eminence (thumb) is detected.
Depending on the therapy to be performed, the stimulation point may be this same motor point or, in the case of depressions, it will be displaced to locate the dorsolateral prefrontal cortex. Once in place, the coil arm is fixed and the therapy begins.
During the treatment, a series of taps are felt, which will temporarily cease to be felt. In subsequent sessions it will not be necessary to recalculate the threshold.
The duration of the procedure will be variable and will depend on the pathology of the patient to be treated and the protocol used. A typical protocol for depression usually includes between 10 and 20 consecutive sessions lasting between 30 and 45 minutes. In the case of migraines, the protocol establishes 3 sessions on alternate days of about 7 minutes. Therefore, the treatment must be individualized.
Results Transcranial Magnetic Stimulation (TMS)
In general terms it can be said that TMS produces a selective stimulation of certain areas of the brain which, depending on the protocol applied, will produce an increase or decrease in neuronal excitability.
Often there is no noticeable change in mood or other psychiatric symptoms during the first few sessions. In TMS for therapeutic purposes, long-lasting cognitive changes are related to the cumulative effects of repeated sessions in its application to psychiatric and neurological disorders.
TMS can produce several types of biological effects in addition to the purely neurocognitive ones such as:
– Endocrine effects: A response of pituitary-hypothalamus axis hormones (prolactin, TSH, FSH and cortisol) and increased plasma beta-endorphins have been seen in the treatment of migraine.
– Effects on neurotransmitters, such as dopamine, which could induce beneficial effects in Parkinsonian.
– Effects on the immune system by decreasing the number of lymphocytes.
– Autonomic function, since many brain regions are involved in the control of blood pressure, respiration and heart rate.
Some factors that may also influence the results obtained must be taken into consideration:
– The effects may be variable if these are applied in the acute phase of the disease or for prevention.
– Many variables can theoretically contribute alone or in combination to modify the previous stage of neuronal activity and can affect the effects or risk: menstrual cycle, age, anxiety level, sleep deprivation, hidden substance abuse, thinness of the skull layers or brain atrophy.
– Interaction with other forms of therapy such as psychotherapy, neurorehabilitation or drugs, primarily by exerting synergistic or opposing effects.