Transcutaneous electrical nerve stimulation (TENS) is a technique that uses an electrical current to relieve pain. In this sheet, you will discover this practice in more detail, its principles, the different types of neurostimulation, its history, its benefits, how a session takes place, who practices it and what are the contraindications.

Transcutaneous electrical nerve stimulation is a non-drug, non-invasive technique for relieving pain using a low-voltage electrical current transmitted through electrodes placed on the skin. The acronym TENS, by which this therapy is often referred to, comes from its English name Transcutaneous Electrical Nerve Stimulation. The device that generates the desired current and to which the electrodes are connected is called a “neurostimulator”. They can be found in just about all physiotherapy and physiatry clinics. Nowadays, we also make very small ones that run on batteries and that can be carried around like a walkman.

The main principles

The mechanisms by which electric current can relieve pain have not yet been elucidated. Nevertheless, there are currently two main hypotheses to explain this analgesic action: the gate theory and the stimulation of endogenous production of natural analgesics.

The gate theory, or theory of the controlled passage of pain, was first formulated by the creators of transcutaneous neurostimulation, Ronald Melzack and Patrick Wall. According to this hypothesis, the electric current sent to the nerves would help block the passage of painful information to the brain. The gate would thus be closed between the nerves and the spinal cord, the normal route of transmission of nerve impulses to the thalamus and the cerebral cortex.

As for endogenous analgesics, these are pain-relieving substances that the body produces naturally according to its needs. These are endorphins, enkephalins and dynorphins, substances related to morphine. Their production would be stimulated by the passage of electric current through the nerves.

It is also possible that the analgesic effects of transcutaneous neurostimulation are the result of these two mechanisms combined.

La neurostimulation transcutanée

In conventional transcutaneous neurostimulation, a low voltage electric current is typically employed varying in intensity from 10 mA (milliamps) to 30 mA. The frequency of the pulses is between 40 Hz and 150 Hz (Hertz – pulsation per second).

The electrodes, usually two or four in number, are attached to the skin using adhesive tape. They are placed near the painful area or, depending on the case, along the path of a specific nerve or at other strategic locations. The subject is invited to adjust the neurostimulator so as to find the intensity, frequency and duration of the pulsations which give him the best relief while causing the minimum of discomfort.

The settings, as well as the duration and frequency of treatment sessions, can vary widely from person to person. In some cases the analgesic effect is felt immediately, while in others it will take 30 minutes or an hour of treatment before the pain is relieved. In some patients, the analgesic effect wears off as soon as the treatment is stopped; for others, the relief may last for hours or even days.

Percutaneous neurostimulation

Percutaneous Electrical Nerve Stimulation (PENS) is a more invasive technique that involves directly stimulating one or more nerves using electrodes inserted under the epidermis, which may require minor surgery. It is also possible for a competent practitioner to practice this technique using electrodes which are in fact needles of the type used by acupuncturists. However, this is not acupuncture here, since the practitioner does not seek to stimulate the acupuncture meridians, but rather specific nerves located under the epidermis.

Neurostimulation et acupuncture

Electroacupuncture is a technique that connects acupuncture needles to a low frequency neurostimulator. It is more of acupuncture than of transcutaneous neurostimulation. The electrodes are therefore placed on acupuncture points. In these cases, the frequency is reduced (1 Hz to 10 Hz) and the intensity is increased up to the patient’s tolerance limit.

Although transcutaneous nerve stimulation is widely used in hospitals and physiotherapy clinics, the overwhelming evidence for its effectiveness is relatively poor. It is indeed difficult to design a randomized clinical trial protocol with placebo to evaluate it. People may have electrodes attached to their skin, but they can hardly ignore whether the electric current is flowing or not.

We know, moreover, that the placebo effect is relatively large in terms of pain perception, which can easily distort the results of clinical trials. Consequently, despite an abundant scientific literature, only a few applications (osteoarthritis of the knee and anesthesia in dentistry) are solidly documented. This explains why the effectiveness of transcutaneous neurostimulation remains controversial.

Here is the presentation of the benefits of this technique in view of the scientific literature:

Relieve symptoms of osteoarthritis of the knee

Numerous clinical studies have evaluated the potential effects of transcutaneous neurostimulation in patients with osteoarthritis of the knee. In general, the results indicate a decrease in joint stiffness and pain associated with osteoarthritis. However, there was little improvement in the functional capacity of the patients.

Perform anesthetic action in dentistry or dental surgery

Since the 1990s, studies have shown that the use of TENS during dental procedures can reduce the discomfort associated with anesthetic injections, decrease pain during the procedure and reduce medication intake.

Improve memory impairment in patients with Alzheimer’s disease

Clinical studies have concluded that transcutaneous neurostimulation may improve some symptoms in patients with recent Alzheimer’s disease, primarily memory and mood. A placebo study found significant improvement in cognitive function and short-term memory in patients with Alzheimer’s disease after four weeks of TENS. However, after six months, no difference was observed between the two groups.

Relieve pain associated with dysmenorrhea

In 2002, one evaluated the effectiveness of TENS in relieving pain caused by dysmenorrhea. The results turned out to be contradictory. In 2007, two small studies observed that transcutaneous neurostimulation could act in the short term on the pain felt during menstruation.

Relieve pain during childbirth

In a 2007 study, women in both groups (TENS and TENS placebo) were stimulated on two specific acupuncture points. Women receiving true transcutaneous nerve stimulation experienced less pain in the first phase of labor than those in the placebo group. The authors conclude that it could be a useful complementary therapy.

Relieve chronic lower back pain

The effects of transcutaneous neurostimulation or electroacupuncture to treat chronic low back pain have been the subject of several controlled clinical studies to date and the results remain controversial. Experts concluded that TENS could be used as an immediate additional treatment to reduce pain in the short term. However, they would not have had a positive effect on pain reduction in the long term.

In addition, other research has shown that electroacupuncture could decrease the pain of individuals suffering from rheumatoid arthritis of the hand, relieve migraines or even relieve pain related to radiculalgia and various chronic pain (osteoarthritis , pancreatitis, myofascial syndrome, diabetic neuropathy, low back pain).

The specialist

Most of the time, transcutaneous nerve stimulation treatments are given in hospitals by healthcare professionals, or in physiotherapy clinics, usually on the recommendation of a doctor.

Course of a session

The first session is a test session during which the practitioner will try different types of stimulation and settings in order to determine the optimal treatment. Depending on the goal, the session can last from a few minutes to several hours. As for the number of sessions, it will of course depend on the objective, but also on the methods of the electrical stimulation (intensity, type of current, etc.) and the physical conditions of the patient.

When the treatment must be repeated several times a day, it is possible to use a portable neurostimulator that can be used at home or at work. Some hospitals and treatment centers provide it for their patients.

Become a practitioner in electrical neurostimulation

There is no official training in this technique. Generally, hospital staff are trained in this technique by physiotherapists through in-house training. Physiotherapists usually administer transcutaneous neurostimulation treatments as prescribed by a doctor.

Contraindications of electrical neurostimulation

This technique has some contraindications. Thus, people who have had a pacemaker implanted cannot receive transcutaneous nerve stimulation treatment. As for pregnant women, neurostimulation can prematurely trigger contractions.

In general, the electrodes should not be placed near the heart, on the front of the neck, on the head, near the eyes, on a wound or very sensitive areas.

On some stone tablets dating from ancient Egypt (2500 BC), some traces of the use of rays and electric torpedoes to relieve pain have been found. The fish were placed on the painful areas. In Socrates’ day, arthritis pain and headaches were treated like this. However, it was not until 1965 that Ronald Melzack (psychologist) and Patrick Wall (physiologist) systematized the technique and gave it the name of “transcutaneous electrical neurostimulation”. Today, this technique is commonly used in hospitals and clinics to relieve different types of pain, usually in combination with other approaches, drug or physical.