Electromyogram: everything you need to know

Electromyography can be defined as the graphic recording technique of electrical activity produced by skeletal muscles. This electrical activity is known as electromyogram (EMG). At a diagnostic level, the test allows detecting muscle or neurological damage, degenerative diseases and diabetic neuropathy, among others.

For informational purposes, we are going to use the concepts electromyogram and electromyography interchangeably, since there does not seem to be an exact consensus in medical portals on which is the most indicated. Even so, it seems that the term "electromyography" is used to designate the technique used, while the electromyogram is the test and the result.

Beyond details at the linguistic level, it is clear that these procedures are very useful for measure the electrical activity of muscles and nerves. If you want to know everything about the test and in which patients it is indicated, continue reading.

What is an electromyogram (EMG)?

As indicated by the US National Library of Medicine, electromyography and nerve conduction studies are used to measure muscle and nerve activity. Nerves send electrical signals to skeletal muscles to contract And when they react, they emit signals that can be quantized.

The electrical source recorded is the muscle membrane potential, that is, the difference in potential between the inside and outside of the muscle cells. The potential ranges measured by the EMG are from 50 μV to 20-30 mV, depending on the type of muscle being observed.

The electromyogram is used to find out if a patient has a muscle, nerve, or both types of problem. However, it is usually done in conjunction with a nerve conduction study. Both differ between them by the following premises:

  • The EMG examines the electrical signals from muscles when they are at rest and at work.
  • Nerve conduction studies measure how quickly and effectively nerves transmit electrical signals.

We are facing 2 complementary processes, but they are not measured in the same way. For example, EMG requires the use of a needle electrode, while nerve conduction studies are done with discs attached to the skin.

To know more: 7 steps to interpret an electrocardiogram

Why is an electromyogram performed?

According to the World Health Organization (WHO), approximately 1.710 million people worldwide have some type of musculoskeletal disorder. This makes musculoskeletal problems leading cause of disability on the planet, the main culprit being lumbago.

These disorders limit the mobility, dexterity, work capacity and autonomy of patients who present them in their most severe forms. Therefore, making a proper diagnosis and acting quickly is essential.

Here we present the group of symptoms that may indicate the need for an electromyogram.

Evaluating muscle pain of doubtful origin may require the use of an electromyogram.

1. Muscle weakness

Muscle weakness or myasthenia, as the name implies, It is characterized by the lack of strength of the patient's musculature. This can be true or acquired, that is, it can be caused by dystrophies in the muscle tissue or by emotional conditions.

There are a total of 5 degrees of muscle weakness, the fifth being a normal force contraction and the first a total absence of it. The electromyogram can help place the patient on some of the values ​​on this scale.

2. Tingling and numbness of extremities and face

Numbness and tingling are often caused by staying in one position too long, but if these are continuous or too recurrent, a pathology can be suspected. Among them we find lesions on the nerves, pressure on the spinal nerves, herpes zoster infection and lack of blood supply.

3. Muscle cramps, spasms and contractions

As indicated in the MSD Manuals, a cramp is a brief, involuntary and painful contraction of a muscle or group of muscles. Most of them are benign, as they occur for unknown causes at night or during times of demanding physical activity.

However, some nervous and metabolic disorders, such as hypothyroidism, low levels of electrolytes in the body, dehydration and other conditions can cause spasms to appear more than normal.

4. Muscle paralysis

Paralysis is the loss of muscle function in one part of the body. This symptom is serious and requires an immediate medical approach. From severe injuries to strokes, paralysis is an entity that does not bode well for a very positive prognosis.

How is an electromyogram performed?

For the test, the following steps are followed in the relevant hospital:

  1. The patient should sit or lie down on a table or stretcher. The professional will thoroughly clean the area to be examined.
  2. After that, a needle electrode is inserted into the muscle area of ​​interest. The patient may feel mild pain or discomfort at this point.
  3. When the electrodes are in place, the machine used records the activity of the muscle at rest. The practitioner will then ask the patient to contract the muscle tissue of interest. This is how changes in the membrane potential and hence the electrical intensity are recorded.
  4. The needle electrode can be inserted into other muscle tissues to quantify its activity.
  5. Electrical activity is seen in the form of wavy, pointed lines on the video screen of the machine. It can also be heard through a loudspeaker.

An electromyogram can last approximately 30 to 60 minutes. It should be noted that this test is usually accompanied by a nerve conduction study that will last from 15 minutes to more than 1 hour, depending on the muscles and nerves being studied.

How to prepare for the test?

If the patient has a pacemaker or a cardiac defibrillator, it should be clearly communicated to the professional. In general, these people have electrical stimulation avoided in the neck area.

On the other hand, it is recommended to wear loose clothing and easy handling to allow the professional to access the muscle group to be analyzed more quickly. It is also essential not to use lotions, perfumes and other substances on the affected area a couple of days before the test.

The study allows to approach almost all the superficial muscles, although it is more common to do it in the limbs.

Possible risks

The risks of this test are almost nil, as it is a minimally invasive diagnostic method. In any case, the Mapfre Health portal shows us some small adverse effects that must be taken into account:

  • Minimal bleeding at the electrode application point.
  • Infection in the area of ​​application.
  • Local allergic reaction after needle insertion.

Depending on the sensitivity of each patient, the electromyogram is a study that can be annoying and painful. Anyway, in most cases the discomfort is tolerable and the only side effect is the appearance of a small bruise.

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A simple and easy test to perform

As you can see, the electromyogram is a simple and easy test it won't take more than an hour of your time in almost no setting. In addition, no special preparation is required to perform it. At most, keep the skin naturally sanitized and go to the consultation with loose clothing.

It is very useful for detecting failures and dysfunctions at the muscular and neurological level. Many of these pathologies are treatable if they are detected early, so if you feel that your muscles are weak or you have problems when making efforts, do not hesitate to go to the medical consultation.