a set of arms doing the tensilon test for myasthenia gravis, each arm has growing muscle

What Is the Tensilon Test?

The Tensilon test is a procedure once used to help diagnose myasthenia gravis (MG). It has not been used in the United States in years. Other types of tests are considered more accurate, but you may still hear about it today.

The Tensilon test is a diagnostic tool used to help decide whether someone has MG or not, not a treatment for MG. It may also help differentiate between MG and other brain and nervous system conditions.1,2

How is performed?

The test must be done in a healthcare setting – usually at the bedside – so that you can be closely monitored by your doctor. The test is usually done in incremental doses.

First, a small amount of the drug Tensilon (edrophonium chloride) is injected into your arm or hand via an IV needle. Once injected, the drug usually kicks in within 30 to 45 seconds.1,3

Your doctor will then ask you to perform a series of movements over and over again to see if the drug is working. Some of these movements may be:4

  • Crossing and uncrossing your legs
  • Standing up and sitting down
  • Raising your arms above your head until they get tired
  • Taking a series of deep breaths
  • Repeating the same sentence several times

The small amount of Tensilon that is injected only lasts in the body for about 5 to 10 minutes. So, during the span of the procedure, multiple, smaller doses of the drug (usually about 2 milligrams) are given. After each subsequent dose, your doctor will have you repeat the movements again.1,3

What is the drug doing?

Tensilon prevents the breakdown of a chemical in the body called acetylcholine. When working properly, nerve cells release acetylcholine in order to activate muscles.3

But people with MG do not have normal reactions to acetylcholine. This is why their muscles tire more easily.

What do the results mean?

If a person begins to feel a sudden improvement in muscle strength, it could mean that they have MG. However, not everyone with MG will improve with a Tensilon test.1

Whether the Tensilon test shows results or not, additional testing is recommended to get an accurate diagnosis. This typically includes blood tests and imaging tests such as a magnetic resonance imaging (MRI).1

Are there any side effects?

Some people may experience an upset stomach or increased heart rate after a Tensilon injection. These are usually mild and go away once the dosage has worn off.4

In rare cases, side effects can include worsening muscle weakness, a drop in heart rate, slowed breathing, or low blood pressure. A drug called atropine is typically given to reverse these side effects. They are why Tensilon tests are closely monitored by a doctor.3

Why is it no longer used in the United States?

The Tensilon test had been used to help diagnose MG since the 1930s. But because of the high number of false positives, the U.S. Food and Drug Administration discontinued the use of the drug. As of 2018, it is no longer used in the U.S. and many other countries.1,3

More reliable tests like serological antibody tests and repetitive nerve stimulation (RNS) tests are now used to get an accurate diagnosis of MG.1

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