What's an Edrophonium Test and What is it for?

An edrophonium test helps to diagnose myasthenia gravis. It also helps to choose the most appropriate dose of treatment and to follow up. We'll explain how it works in this article!
What's an Edrophonium Test and What is it for?

Last update: 03 August, 2021

An edrophonium test, also called Tensilon® test, is a pharmacological test. It consists of injecting edrophonium bromide or edrophonium chloride, which are substances that react with the transmission of nerve impulses at the muscular level.

The objective’s to study a patient’s muscular fatigue. Therefore, doctors prescribe it to diagnose and assess the response to treatment in myasthenia gravis.

This test is considered effective and is the most commonly used test for this disease. However, it must be performed with several precautions. In this article, we’ll explain what the edrophonium test is and what it involves.

What is the edrophonium test?

The edrophonium test, in addition to being called the Tensilon® test, is also called the Anticude® test. These names vary because they refer to the brand name of the drug.

Tensilon® is edrophonium chloride, while Anticude® is edrophonium bromide, as a publication of the Agència Valenciana de Salut explains. These drugs act at the neuromuscular level and prevent the breakdown of acetylcholine, which is a neurotransmitter that acts in the neuromuscular plate.

That is, in the area where neurons bind to muscle fibers to stimulate them. By inhibiting the breakdown of acetylcholine, what happens is that a more marked muscle stimulation occurs.

Therefore, the edrophonium test consists of observing what response takes place at the muscular level. There are diseases, such as myasthenia gravis, in which there are changes in the muscle fibers due to acetylcholine. Therefore, it’s useful in diagnosing and monitoring this disease.

A woman with a sore calf muscle.
Neuromuscular diseases, such as myasthenia gravis, can manifest themselves with weakness or pain in the affected areas, such as the lower limbs.

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When is the edrophonium test necessary?

Doctors usually order the edrophonium test when there’s suspicion that the patient has myasthenia gravis. They also use it to control the dose of anticholinesterase drugs when a diagnosis of the disease has already taken place and the patients taking these drugs as treatment.

As explained in the previous section, the neuromuscular plate is the site where nerves and muscle fibers communicate. In this area, the nerve secretes a neurotransmitter called acetylcholine, which binds to muscle receptors.

In myasthenia gravis, the immune system produces antibodies that block or destroy the acetylcholine receptors. As a result, the muscle receives less stimulation. Therefore, there’s weakness and rapid muscle fatigue.

In myasthenia gravis, the weakness worsens with the use of the affected muscle. According to Mayo Clinic specialists, symptoms improve with rest.

As the years go by, symptoms progress, and periods of rest no longer compensate for the weakness. More than half of the patients begin with signs in the eye muscles. Therefore, two very typical symptoms are drooping of the eyelid and double vision.

What does edrophonium do for myasthenia gravis?

The edrophonium test causes no breakdown of acetylcholine. An enzyme called acetylcholinesterase is responsible for this breakdown. As it’s not broken down, there is more concentration. Therefore, muscle stimulation is greater.

When a patient with myasthenia gravis undergoes the edrophonium test, the muscles are more powerful. In addition, this test also makes it possible to evaluate which is the most suitable treatment in terms of dosage.

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Previous preparation

Before performing the edrophonium test, it’s important to take certain aspects into account. The physician must know what medications the patient is taking, including supplements or other herbal remedies.

The reason is that many of these substances can interfere with the result. For example, the ones that most often alter the edrophonium test are acetylcholinesterase inhibitors. These are drugs used to treat dementia, such as donepezil and rivastigmine.

The idea is that the physician will advise whether or not the patient must discontinue their use before undergoing the test. It’s also possible that the doctor may impose some dietary restrictions during the days leading up to the test.

How is the edrophonium test performed?

A physician performs the edrophonium test and it usually takes place in a specialized neurology office. First, a specialist places an intravenous needle into the patient’s arm or hand.

Then, they inject a small amount of edrophonium through the needle. To begin to study whether myasthenia gravis is present, the physician asks the person to make repetitive movements.

As an article by Servizo Galego de Saúde explains, the movements can be with different parts of the body. For example, getting up from a chair, crossing and uncrossing the legs, keeping the arms raised. The test also studies the voice, asking the patient to count backward from 100.

During the edrophonium test, several doses of the drug are injected. This tests whether the muscle regains strength after each injection. If it does, then the doctor will make a diagnosis of myasthenia gravis.

What does the result mean?

The results of the edrophonium test are usually immediate. As we explained in the previous section, the patient receives a diagnosis of myasthenia gravis if, after each edrophonium injection, the muscle regains some strength.

However, in some cases, other tests are necessary to confirm the diagnosis. In this case, if edrophonium produces a transient stimulation, it means that the disease has worsened. On the other hand, if injecting the drug weakens the muscle, the test points to an overdose of anticholinesterases.

A doctor preparing an injection.
The test takes place in a neurology office, with strict control of the doses.

Risks and recommendations

Experts consider the edrophonium test to be effective and safe. However, there are several side effects that occur frequently. However, they’re brief and don’t usually last more than a few minutes.

Nausea and stomach pain are two of the most common effects. Shortness of breath, sweating, dizziness and blurred vision may also occur. Other patients experience eyelid twitching, increased salivation, and even fainting.

As with any injection, the site of the injection may bruise. Ideally, the patient should apply pressure or ice during the first 24 hours to reduce swelling.

There are few cases in which the edrophonium test has serious repercussions. Therefore, experts don’t recommend it for people with baseline arrhythmias, low heart rate, or arterial hypotension.

The same is true for patients with sleep apnea and asthma. Although there are indeed limited side effects, in cases where discomfort persists, a specialist can administer an atropine injection to reverse the effects.

Myasthenia gravis is the main reason for this test

An edrophonium test is a useful test to diagnose myasthenia gravis. It’s also useful for monitoring the treatment of this condition.

Problems with drug dosage are common. It’s important to test these patients regularly to avoid serious complications. In addition, experts consider this test to be safe and effective, as long as it takes place in a controlled environment.

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