What to Expect From a Tensilon Test

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A Tensilon test is a diagnostic test used to evaluate myasthenia gravis, which is a neuromuscular condition characterized by muscle weakness. The test involves an injection of Tensilon (edrophonium), after which your muscle strength is evaluated to determine whether your weakness is caused by myasthenia gravis or not.

myasthenia gravis
Verywell / Alexandra Gordon


The most common reason to have a Tensilon test is to differentiate between myasthenia gravis and other conditions that cause weakness. The weakness of myasthenia gravis typically worsens after physical activity and improves after resting.

The most common symptoms of myasthenia gravis include double vision, droopy eyelids, slurred speech, and weakness and tiredness of the arms or legs. The symptoms are generally worse late in the day, and the weakness can affect the muscles that control your ability to breathe as well, which means that you have to exert effort to breathe.

The condition usually starts in adulthood, can affect men and women, but may occur as a childhood form during infancy as well. If you have myasthenia gravis and are not diagnosed and treated, you will continue to experience symptoms.

Other Conditions

Conditions that produce symptoms similar to those of myasthenia gravis include cholinergic crisis, which can occur as a result of toxin exposure or anesthetic overdose, or Lambert Eaton syndrome, a neuromuscular condition caused by underlying malignancy. These are all rare conditions.

How the Test Works

The reason a Tensilon test can help in the diagnosis of myasthenia gravis is that Tensilon biochemically counteracts the effects of the disease. The disease is an autoimmune condition, which means that body attacks itself.

If you have myasthenia gravis, your body’s immune system attacks the region on your muscles that should normally be activated by your nerves. Nerves typically release a neurotransmitter, acetylcholine, which binds to acetylcholine receptors on muscles to activate them.

In myasthenia gravis, your immune system attacks the acetylcholine binding sites on your muscles, which prevents them from responding to acetylcholine. This prevents your muscles from working as they normally should, which manifests as muscle weakness.

Because you still have some intact acetylcholine receptors even if you have myasthenia gravis, the disease does not make you completely paralyzed, and instead, it causes you to become weak after you have used your muscles for a while.

Tensilon reverses the symptoms of myasthenia gravis. It works by preventing your acetylcholine from breaking down. It inhibits the enzyme that normally breaks down acetylcholine, acetylcholinesterase, allowing your acetylcholine to bind to the existing receptors as much as possible. Tensilon works very quickly, and you and your healthcare providers can observe the effects of the injection right away.

What to Expect

This is an interventional test that requires an intravenous (IV) injection of the medication. You will need to participate in some repetitive physical actions and describe your symptoms in order for your healthcare provider, usually a neurologist, to assess the results of your Tensilon test.

The steps of the test include:

  • Preparation: If you are taking other cholinesterase inhibitor medications, they can interfere with the results of a Tensilon test, so your healthcare provider may ask you to stop taking them. Cholinesterase inhibitors Aricept (donepezil) and Excelon (rivastigmine) are used for the treatment of dementia. Do not stop your medications before a Tensilon test without discussing with your healthcare provider first.
  • Initial injection: Your healthcare provider will inject 2 milligrams Tensilon IV at first. This is not the whole dose needed for the test and this initial injection is used to observe for Tensilon side effects.
  • Observation for side effects: After the partial dose is injected, your healthcare provider will observe you for about two minutes for side effects, which can include slow breathing, slowed heart rate, and low blood pressure, before proceeding with the rest of the test.
  • Complete the injection: If you don’t have adverse effects from the initial test dose, your healthcare provider will inject the remaining 8 milligrams of Tensilon for the test.
  • Describe your symptoms: If you notice any changes in your vision, strength, breathing, or sense of balance, you should be sure to describe these effects to your healthcare providers.
  • Engage in physical activity: Your healthcare provider may examine your muscle strength and will ask you to do some physical actions, such as repeatedly standing from a seated position, to assess your muscle strength.
  • Reversal of medication, if needed: If you have an adverse reaction to the test, such as worsening weakness, or a slow heart rate, slowed breathing, or low blood pressure, you can have the effects rapidly reversed with an injection of atropine, which works against acetylcholine.


The results of a Tensilon test can be evaluated by a brief observation of the effects of the medication after injection. There are not generally measured laboratory values, and the effect of Tensilon only lasts for approximately 10 minutes.

If your strength increases in response to Tensilon, then it is likely that you have myasthenia gravis. There are other evaluations that can be done to assess changes with a Tensilon test if myasthenia gravis is suspected, including evaluation of your swallowing function with a test called an endoscopy that evaluates the swallowing muscles. However, not everyone with myasthenia gravis improves with a Tensilon test.

Other conditions such as blepharospasm and cervical dystonia are expected to worsen with a Tensilon test. If you have Lambert Eaton syndrome or a cholinergic crisis, then you should not improve with a Tensilon test, and your symptoms might even worsen.

Next Steps

After your Tensilon Test, if your test is diagnostic of myasthenia gravis, your healthcare provider will likely start you on medication. Treatments for myasthenia gravis include steroids to suppress the immune system, plasmapheresis to counteract the autoimmune process, Mestinon, Regonol (pyridostigmine), which is an anticholinesterase inhibitor, or thymectomy (removal of the thymus), a surgery to reduce autoimmune activity.

If your test was not diagnostic, then your healthcare provider will continue your diagnostic evaluation to identify the cause of your weakness with tests such as electromyography (EMG), nerve conduction studies (NCV), and blood tests.

A Word From Verywell

If you need a Tensilon test, you will need to participate in the required physical activities during the test, and it will help in your diagnosis if you explain how your symptoms change during the test. You do not need to be concerned about long-term problems from the test because the medication only has an effect for 10 minutes, and adverse effects can be rapidly reversed. 

Myasthenia gravis is a chronic disease that requires long-term treatment, but some people notice partial improvement of the disease over time.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

By Heidi Moawad, MD
Heidi Moawad is a neurologist and expert in the field of brain health and neurological disorders. Dr. Moawad regularly writes and edits health and career content for medical books and publications.