Electromyography ( EMG )
Electromyography (EMG) refers to a mandatory study for suspected damage to the neuromuscular system. EMG is a painless procedure, does not require preliminary preparation, and its indicators are informative enough to make a diagnosis. This makes muscle electromyography an indispensable study in neurological practice.
Electromyography: what is it?
Electromyography is a method for diagnosing disorders of the neuromuscular system, based on indicators of the bioelectrical activity of muscles. The study is based on the ability of muscle tissue to create electrical activity with each contraction. Depending on the indicators, taking into account the accompanying clinical picture, the lesion focus and its localization are determined.
An EMG is performed using an electromyograph . The device registers bioelectrical activity, transmitting it to the monitor screens or recording it on paper.
Conducting electromyography allows you to establish:
Localization of the pathological focus.
The nature of the pathology. Damage to muscle or nerve fibers is determined.
Degree of spread of the process.
The stage of the disease.
Damage level. There may be a local or systemic disease. Depending on this, the type of research is selected.
The dynamics of the pathological process.
Types of EMG
There are several ways to perform electromyography. The choice of method is carried out by the doctor depending on the existing pathology.
Stimulation (surface) electromyography
Refers to a non-invasive and painless study. This EMG method allows you to evaluate the bioelectrical activity in a large area of the muscles. Stimulation myography is performed on the lower and upper extremities in order to study weakness, fatigue, numbness, and decreased muscle sensitivity. In addition, surface EMG is performed to diagnose nerve damage. This type of study evaluates the state of masticatory and facial muscles, which is informative for cosmetologists and dentists.
Needle (local) electromyography
Used for more precise research. For this purpose, a needle electrode is inserted into the muscle. In this case, there is a slight soreness, which soon passes. Local electromyography refers to an invasive research method. In this regard, after the procedure, hematomas or infiltrates may occur.
Difference between EMG and ENMG
Often there are two names for the study: “electromyography” ” electroneuromyography “. Electromyography is needle and stimulation . Needle electromyography is called EMG, and stimulation is called ENMG ( electroneuromyography ). There is no significant difference in how the study is called. Neurophysiologists, in order to comprehensively study the pathological process, perform a combined study, which consists of stimulation and needle methods.
Indications for electromyography
High accuracy, painlessness of the procedure make it mandatory in the presence of pathology of the neuromuscular apparatus. Common indications for an EMG include:
The appearance of weakness in the muscles, increased fatigue.
The presence of a convulsive syndrome.
Violation of sensitivity.
Decrease in muscle volume.
Pain in the muscles of varying severity.
Most often, EMG is used in neurological practice. Diseases requiring electromyography include:
Polyneuropathy.
Muscle pathology: inflammation, dystrophy, fatigue.
Degenerative-dystrophic changes in the spine.
Hyperkinesis (involuntary muscle movements).
Tremor in parkinsonism.
Radiculopathy (damage to the nerve roots).
Traumatologists and orthopedists, when choosing a prosthesis, must prescribe electromyography to assess the lost functions of a limb. Diagnosis of muscle conductivity is actively used in cosmetology for the introduction of Botox.
EMG of facial muscles and nerves
Electromyography of facial muscles allows assessing the state of masticatory and facial muscles, suspect brain pathology, identify typical changes in neuromuscular transmission in myasthenia gravis and myasthenic syndrome. Using electromyography, neurologists-neurophysiologists determine the cause of temporomandibular joint dysfunction, obtain important information for prescribing optimal treatment for facial hemispasm and other diseases.
Electromyography of the facial and trigeminal nerve
EMG of the facial nerve helps to determine the cause of weakness or increased excitability of the masticatory and facial muscles, and the trigeminal nerve – to determine the cause of pain, impaired facial sensitivity and function of the masticatory muscles. Neurophysiologists record the electrical activity of facial muscles and the nerves that are involved in controlling these muscles using various types of electrodes.
Indications for EMG facial muscles
Violation of sensitivity and pain in the face;
Omission of the upper eyelid and corner of the mouth, smoothness of the nasolabial fold;
Increased fatigue in the muscles of the face;
Muscular twitching in the face;
Dysfunction of the temporomandibular joint;
Atrophic changes in the muscles of the face;
Local muscle spasms in the facial area.
In some cases, EMG can detect changes in the state of nerves and muscles before the onset of symptoms of the disease, which contributes to early treatment and a favorable prognosis of the disease. Electromyography is used to evaluate the effectiveness of therapy and prognosis in idiopathic facial neuropathy (Bell’s palsy).
Contraindications
Contraindications for EMG are common to all diagnostic procedures. These include:
Infectious or non-infectious diseases in the acute stage.
The presence of a pacemaker.
Skin lesions (pustules, cracks, wounds, fungal diseases).
Epilepsy.
Cardiovascular pathology (hypertensive crisis, myocardial infarction, unstable angina).
Mental disorders in which the patient cannot control his actions.
Needle electromyography is contraindicated in violation of blood clotting, as well as increased pain sensitivity.
Electromyography: preparation for the study
EMG does not require special preparation, however, there are several recommendations, the observance of which will provide the most accurate recording of muscle bioelectrical activity. These include:
refusal to take certain medications (tranquilizers, muscle relaxants and other drugs that affect the nervous system)
a few hours before electromyography, it is recommended to stop eating foods that increase nervous excitability (tea, coffee, caffeinated drinks, chocolate, carbonated drinks).
In the case when the cancellation of drugs is not possible, it is necessary to warn the attending physician in advance.
How is electromyography performed?
Electromyography takes 30 to 60 minutes. The time depends on the number of areas to be examined, as well as the severity of the lesion. Electromyography is performed using an electromyograph . It is used to register and record the bioelectric activity of muscle fibers.
The EMG procedure can be performed on an inpatient or outpatient basis. For this, the patient is asked to take a comfortable position (sitting, lying, half-sitting). The area to be examined is treated with an antiseptic. After that, electromyograph electrodes are applied to it . In the case when needle EMG is indicated, a needle electrode is inserted into the muscle under study. This is the only type of electromyography in which a slight pain syndrome is felt. All other methods are painless.
At the beginning of the procedure, the conductance of the muscles at rest is assessed. After that, she is asked to strain, after which the bioelectric activity is recorded again. The results obtained are an electromyogram , which reflects all the changes that occur in the neuromuscular system. Based on the data obtained, a diagnosis is made or an assessment of the treatment is carried out.
EMG decoding
The electromyography technique is based on recording muscle activity. The results obtained form an interference curve reflecting any changes in conductivity.
The following main diseases are distinguished, in which a change in the amplitude of oscillations is recorded on electromyography:
Polyneuropathy. The results of the curve depend on the degree of damage to the nerve fiber. With a mild degree, the frequency of oscillations is significantly reduced. In the case when the pathology of the nerve caused its complete death, “bioelectric silence” is recorded.
Myositis. Inflammation of muscle fibers causes a decrease in their conductivity. Indicators of bioelectrical activity depend on the degree and stage of myositis.
Amyotrophy . Pathology is characterized by loss of muscle mass. At the same time , an increase in the amplitude of oscillations is recorded on the EMG . The curve looks like a “palisade”.
Myasthenia. Muscle fatigue syndrome significantly affects the electrical conductivity of the fibers. On EMG, there is a decrease in the amplitude of oscillations. The values depend on the stage of the disease.
Tremor. A sharp increase in the amplitude of oscillations is registered. Their frequency depends on the localization of the focus.
Myotonia . On EMG, curves with low amplitude and high frequency are determined.
EMG results are interpreted by highly qualified doctors. Based on the data obtained, the specialist is able to establish the localization of the pathological focus, its degree and stage.