What to Know About the Tensilon Test
Medically reviewed by Smita Patel, DO
The Tensilon test was discontinued in the U.S. in 2018. It was performed to help diagnose myasthenia gravis (MG), a neuromuscular junction condition characterized by muscle weakness.
The test involved an injection of Tensilon (edrophonium), after which your muscle strength was evaluated to determine whether your weakness was caused by myasthenia gravis or not.
Read on to learn more about how the test worked and what is currently being used to diagnose myasthenia gravis.
Purpose of the Tensilon Test
The most common reason to have a Tensilon test was to differentiate between myasthenia gravis and other conditions that caused weakness. The weakness of MG typically worsens after physical activity and improves after resting.
The most common symptoms of MG 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 and can affect both 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 Similar 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 rare conditions.
How the Tensilon Test Worked
The reason a Tensilon test was used to 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 the 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 in 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 MG, the disease does not make you completely paralyzed, Instead, it causes you to become weak after you have used your muscles for a while.
Tensilon reverses the symptoms of MG. It works by preventing acetylcholine from breaking down. It inhibits the enzyme that normally breaks down acetylcholine (acetylcholinesterase), allowing acetylcholine to bind to the existing receptors as much as possible. Tensilon works very quickly, and the effects of an injection can be observed right away.
How Was the Tensilon Test Performed?
This was an interventional test that required an intravenous (IV) injection of the medication. The person being tested needed to participate in some repetitive physical actions and describe their symptoms to a healthcare provider, usually a neurologist, to assess the results of a Tensilon test.
The steps of the test included:
Preparation: Cholinesterase inhibitors (e.g., Aricept, Excelon) could interfere with the results of a Tensilon test, so a healthcare provider may have directed stopping these medications before the test. Medications should never be stopped unless under a healthcare provider's direction.
Initial injection: Two milligrams of Tensilon IV were initially injected. This was not the whole dose needed for the test and this first injection was used to observe for Tensilon side effects.
Observation for side effects: After administering the partial dose a healthcare provider would check for side effects (which can include slow breathing, slowed heart rate, and low blood pressure) for several minutes before proceeding.
Complete the injection: If no adverse effects were observed, the remaining 8-milligram dose of Tensilon was injected.
Describe symptoms: If any changes in vision, strength, breathing, or sense of balance were noticed by the person being tested, they were described.
Engage in physical activity: The healthcare provider checked muscle strength by observing some repetitive physical actions performed by the person being tested (such as standing from a seated position and crossing and uncrossing legs).
Reversal of medication, if needed: If any adverse reaction to the test was noted, such as worsening weakness, a slow heart rate, slowed breathing, or low blood pressure, the effects of Tesilon were rapidly reversed with an injection of atropine (which works against acetylcholine).
Results of a Tensilon Test
The results of a Tensilon test were evaluated by a brief observation of the effects of the medication after injection. There were no generally measured laboratory values, and the effect of Tensilon only lasted for approximately 10 minutes.
Other conditions such as blepharospasm and cervical dystonia are expected to worsen with a Tensilon test. If Lambert-Eaton syndrome or a cholinergic crisis is suspected, then symptoms might also worsen with a Tesilon test.
Takeaway
If strength increased in response to Tensilon, myasthenia gravis was viewed as the likely diagnosis. The improvement is temporary, lasting only a few minutes. In some types of MG and with other conditions, weakness can be made worse by Tensilon.
Next Steps
If a Tensilon Test was diagnostic of myasthenia gravis, a healthcare provider would likely prescribe 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 the Tensilong test was not diagnostic, then further evaluation to identify the cause of weakness would be used.
Why Was the Tensilon Test Discontinued?
Because the Tensilon test resulted in a high number of false positives, the U.S. Food and Drug Administration discontinued the use of the drug (edrophonium) in 2018.
Alternative Testing
More reliable tests are now used to get an accurate diagnosis of myasthenia gravis. MG can be hard to diagnose because muscle weakness can be a symptom of many disorders. So, a healthcare provider may order more than one type of MG test to make a diagnosis. These tests include:
Neurological exam: Medical history is taken and a physical exam is performed including checking:
Reflexes
Muscle strength
Muscle tone
Coordination
Balance
Sense of touch and sight
Ice pack test: An ice pack is used to help diagnose MG if one or both eyelids are observed to droop.
Antibody test: This blood test looks for certain types of antibodies that are found in people with MG.
Electromyography (EMG): This measures the electrical signals muscles make at rest and during use.
Nerve conduction study: This measures how fast and how well the body's electrical signals travel down nerves.
Imaging tests: Problems with the thymus gland can be a sign of MG. A CT scan (computed tomography) or an MRI (magnetic resonance imaging) may be ordered to check for an enlarged thymus or a thymus tumor.
Edrophonium test: Edrophonium is a drug that briefly relieves muscle weakness (especially in the eye muscles) in people with MG.
Lung function tests: There are several kinds of lung function tests that measure breathing and how well the lungs are working. In some tests, medicine or a type of gas may be inhaled.
Summary
During a Tensilon test, a drug was administered, physical activities were required, and changes in symptoms were noted. Positive and negative changes were both possibilities. Negative changes were not a concern as the effects of the medication only lasted for about 10 minutes and adverse effects could be reversed rapidly. Use of the Tensilon test was discontinued in the U.S. in 2018, but other diagnostic tests are available.
Read Next: What Is Myasthenia Gravis?
Read the original article on Verywell Health.
