Transcranial magnetic stimulation: the essence of the method, indications, contraindications, research methods

Transcranial magnetic stimulation (TKMS) is a relatively "young" treatment and diagnostic technique. It was proposed in 1980 and was initially used rather narrowly, mainly as one of the additional methods of examination in neurology. But in recent decades, such stimulation has been used to treat various diseases.

What is TKMS and how does it work?

The technique is based on non-invasive action on the central nervous system with the help of a rhythmically changing (in other words, variable) magnetic field. It is created around an electric coil applied to the scalp, when a high-power electric current flowing through it is cycled and switched off by the discharge of capacitors.

The magnetic field used in this technique has a value of about 2-3 T-about the same as in a magnetic resonance imager. This is almost 400 times greater than the natural level of the Earth's magnetic field. The electromagnetic pulse passes through the skin, subcutaneous tissue, aponeurosis and skull bones unhindered, without deviations and fading. It penetrates through all the meninges and overcomes the liquor spaces. In this case, the main changes under the action of an alternating magnetic field appear in the brain tissue. But the walls of venous plexuses and arteries do not react to it practically.

Under the influence of the magnetic field, the cell membranes of neurons are reversibly depolarized, so that nervous impulses are induced in the brain. They are parallel and counter-directed to the current flowing in the coil of the device. The stronger the applied magnetic field, the deeper it is able to penetrate into the brain tissue and the more noticeable the changes that arise. But a significant increase in the power of exposure can be accompanied by the occurrence of a transient headache. This does not pose a health hazard, but it reduces the comfort of treatment.

The average effective penetration depth of the magnetic field is about 2 cm from the surface of the brain. So the zone of induced depolarization captures mainly the cortical substance and only a small part of the underlying white matter. It is this feature that determines the possible clinical effects on the background of therapy using transcranial magnetic stimulation.

What can you expect from TKMS?

When TKMS on the scalp impose an electric coil - a source of magnetic field. The electromagnetic pulse penetrates into the brain tissue, where it exerts its positive effects

The main effect of transcranial magnetic stimulation of the brain is the formation of evoked potentials. The resulting clinical effects may include:

• Motor manifestations in the form of the reaction of certain skeletal muscles. Moreover, motor evoked potentials can be registered in the zone of central paralysis, which is used in medical and rehabilitation programs.
• Activation of associative zones. The consequence of this can be improved learning, increased ability to concentrate, increasing the efficiency of learning, storing and reproducing information.
• Secondary (mediated) changes in the activity of cortical-subcortical connections and deep structures of the head the brain, which can be used to correct motor, behavioral and affective disorders.
• Appearance of sensory-colored sensations and even hallucinations, which is associated with stimulation of cortical areas of analyzers. But this effect is currently of no clinical significance.

Motor effects of TKMS

The impact on the muscular system is one of the most sought after directions of TKMS. This effect is due to local stimulation of motoneurons in the anterior precentral gyrus and the motor pathways starting from them. It should be noted that the additional activation of these structures in a magnetic field arises indirectly. Initially, the work of interneurons is stimulated, followed by synaptic excitation to large motor neurons. And this leads to the activation of the pyramidal tract with the development of motor evoked potentials.

With a local transcranial action of the magnetic field, only the response of those skeletal muscles is induced, whose zone of topographic cortical representation has been stimulated. This makes it possible to have an impact on the muscle groups. This version of TKMS allows to solve a number of problems:

• reduction of pyramidal muscle tone (spasticity) of various etiologies;
• decrease in the severity of extrapyramidal disorders of hyperkinetic and hypokinetic registers;
• increased muscle strength in paralysis of central and peripheral origin (including the facial nerve).

The induced motor potentials during the magnetic stimulation session of the brain can be registered if necessary. This is the basis for the diagnostic technique for determining the functional state of conducting paths. In this case, TKMS is combined with EEG, EMG.

Indications

Transcranial magnetic stimulation has been introduced into clinical practice recently. Currently, there is an active search for new therapeutic and diagnostic capabilities of this technique.

Currently, the indications for TKMS application include:

• ONMK (acute, recovery and long-term periods). In the early stages after a stroke, TKMS can be used for predictive evaluation of the possibility of restoring motor function. As a therapeutic technique helps reduce the severity of paralysis and soften spasticity of muscles. It is also used in post-aphasia aphasia and cognitive decline.
• Multiple sclerosis - mainly to affect motor impairment. But it can also be used as an auxiliary diagnostic technique.
• Post-traumatic (including postoperative) motor disorders.
• Alzheimer's disease and dementia of another etiology. There is evidence that TKMS can slightly improve cognitive functions with their initial and moderate decline.
• Attention Deficit Hyperactivity Disorder in Childhood.
• Radiculopathy and myelopathy.
• Bell's paralysis.
• Autism and autism spectrum disorders.
• Delay in verbal and psychomotor development.
• Parkinson's disease. TKMS in this pathology is used to activate neurons of black substance in order to stimulate the production of dopamine.
• Depressive syndrome. In the US, Israel and a number of European countries, TKMS is used in the therapy of "large" endogenous monopolar depressive episodes and neurogenic anxiety-depressive conditions. There are data on the use of this method to overcome the resistance to the antidepressants used.
• Pituitary disorders. In the Russian Federation, from 29.12.2012 TKMS is included in the standards of specialized medical care for neoplasm neoplasm and primary health care for children with a delay in sexual development. This is regulated by the Order of the Ministry of Health of the Russian Federation No. 1705n "On the order of organization of medical rehabilitation".

Specialists of some foreign clinics are attempting to use transcranial magnetic stimulation of the brain for the treatment of psychotic disorders in schizophrenia.

When TKMS can not be done

Patients in whom the pacemaker is implanted are not allowed to carry out TBCs

Absolute contraindications for carrying out magnetic transcranial stimulation include:

• The presence in the body of the patient (in the head, neck, chest) implanted non-removable devices with metal elements. It can be pacemakers, pacemakers, pumps and pumps, cochlear implants, hearing aids, devices for deep stimulation of brain structures.
• The presence of foreign bodies and implanted metal medical implants in the zone of electromagnetic waves.

It is also not recommended to stimulate the brain if the patient's disease is associated with a high risk of convulsive syndrome. At the same time, many doctors who use TCM in their practice consider this contraindication to be relative. There are even reports of the beneficial effect of such therapy on the functional state of the brain in patients with epilepsy. And yet, the presence in the history of craniocereberal trauma (especially with local damage to the brain tissue and hematomas), meningoencephalitis, abscesses brain and a number of other diseases requires an individual solution of the question of the possibility of using transcranial magnetic stimulation.

Pregnancy is also referred to as relative contraindications. After all, the zone of action of the therapeutic magnetic field is at a considerable distance from the fetus. But at the same time, a change in the functional activity of the brain can lead to hormonal changes, which potentially can become a risk factor for abortion.

Treatment is postponed with the development of a febrile state, the appearance of signs of any intoxication and an infectious disease.

How to conduct TKMS

Transcranial magnetic stimulation of the brain does not require special preparation. The general recommendations include the refusal to take alcohol, potent and narcotic drugs, it is also necessary to avoid physical overload and overheating. It is undesirable to conduct a session in the first few days after a radical change in the treatment regimen.

Stimulation is carried out using a specially designed apparatus. For the transcranial effect, inductors (coils) of various designs are used. They come with an additional (forced) cooling system and without it. And in form - annular, double and double angular (in the form of a straight and curved figure 8). The choice of the inductor depends on how powerful and focused it is to obtain a magnetic field.

Coyle is placed above the skin (hair) in the projection of the zone chosen for stimulation. At the same time avoid touching them to the body in order to avoid a burn. The effect on the brain tissue can have a different intensity and is carried out in several modes:

• monophasic when the current is fed in one direction and has the form of a rapidly increasing and exponentially decreasing curve;
• monophase pair, consisting of two paused monophasic stimuli, each of which can have its own parameters;
• biphasic with current in the form of a single damped sinusoid;
• burst-bi-phase - in the form of a series of biphasic stimuli.

The treatment session usually lasts 20-40 minutes. It includes 1-3 sessions for 100-200 high-frequency or low-frequency rhythmic stimuli. The impact zones and modes can be combined with each other, with differences in the hemispheres and points of application. The program is selected individually, depending on the therapeutic tasks, the etiology of the disease, the clinical response to ongoing stimulation.

TKMS sessions can be conducted daily or once every few days. On average, the course requires 7-10 visits to the doctor. Most often it is recommended to repeat treatment in 1-3 months.

Possible side effects

Serious side effects in TKMS are rare and rarely require withdrawal of treatment. The most likely undesirable consequences are:

• Development of generalized convulsive syndrome. The risk of its occurrence is associated with the presence in the brain of foci with increased electrical activity, general convulsive readiness. It occurs very rarely, but it is the most serious potential complication of TKMS.
• Headache. They are usually transient and are not accompanied by aggravation of the existing neurological symptoms.
• Tics of mimic muscles, trigeminal pain. In most cases, they are eliminated after changing the position of the inductor and the force of the impact.
• Hearing loss.
• Discomfortable sensations in the place of application of the coil.
• Dizziness.
• Feeling of fatigue, total frustration.

But in most cases, TKMS does not provoke the appearance of significant discomfort and is well tolerated even by young children and patients with several concomitant diseases. Therefore, this technique is considered promising and is increasingly used in neurology, rehabilitation, child psychoneurology. And the testimony to its application is actively expanding.

A cognitive video about transcranial magnetic stimulation:

Transcranial magnetic stimulation of the brain. Center for Radiation Diagnostics.

Watch this video on YouTube