Tensilon test remains a reliable tool for diagnosing MG, per real-world data
Researchers say test, no longer used in US, is still safe, effective
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- Use of the Tensilon test, though discontinued by the FDA, is still safe and effective for diagnosing myasthenia gravis, a new study suggests.
- The diagnostic tool, also known as an edrophonium test, was found to accurately identify people with MG versus those without the autoimmune disease.
- The researchers suggest the test may be useful for ocular MG or when antibody results are pending.
The Tensilon test, though no longer used in the U.S., is generally safe and can accurately identify people with myasthenia gravis (MG) versus those without the autoimmune disease, according to a large study in Austria that assessed the effectiveness of the diagnostic tool.
Also known as the edrophonium test, it’s a so-called bedside test — meaning it’s easily used in a hospital or clinic — that’s used to discriminate people who have MG from those who don’t. In this study, using real-world cases, scientists in Austria evaluated how well the test works.
“We provide data on the diagnostic performance and safety of the edrophonium test, supporting its use as an adjunctive diagnostic test for the diagnosis of MG,” the researchers wrote.
Their findings were detailed in a study titled “Diagnostic performance and safety of the edrophonium test in myasthenia gravis: a retrospective case-control study,” which was published in the journal Neurological Research and Practice.
An immune sytem condition, MG is usually caused by self-reactive antibodies that target proteins, most commonly acetylcholine receptors (AChRs), involved in nerve-muscle communication. Because its symptoms overlap with those of many other diseases, several tests may be needed to identify MG.
Common symptoms make an MG diagnosis challenging
Diagnosis typically involves an assessment of symptoms, blood tests to measure self-reactive antibodies, and a neurophysiological examination.
“Together with antibody testing, repetitive nerve stimulation (RNS) or single-fibre electromyography (SFEMG) are recommended as the standard neurophysiological tests for the diagnosis of MG,” the researchers wrote.
RNS is used to identify changes in nerve-muscle communication with multiple rounds of stimulation, while SFEMG assesses responses of individual muscle fibers.
“However, RNS and SFEMG are not available in all centres … [and] are associated with various limitations, such as a lower sensitivity of RNS in ocular MG [when the disease affects only eye-related muscles] or lower specificity of SFEMG for the diagnosis of MG,” the researchers wrote.
A test’s sensitivity refers to its ability to correctly identify people with a given disease, while specificity refers to its ability to correctly rule out those without the condition.
Given these diagnostic challenges, assessments such as the Tensilon test may serve as complementary diagnostic tools, the researchers noted.
The test, used since the early 1930s to diagnose MG, requires injecting patients with edrophonium chloride, a compound that blocks the enzyme that rapidly breaks down acetylcholine, a key protein for nerve-muscle communication. The compound’s use is expected to temporarily ease MG symptoms, thus allowing for a diagnosis by clinicians.
Its use was discontinued by the U.S. Food and Drug Administration in 2018 due to safety concerns and the availability of better diagnostic methods. Still, the test continues to be used in some regions of the world.
However, despite its longtime use, there remain limited data on its diagnostic performance and safety.
Evaluating the safety and effectiveness of the Tensilon test for MG
To learn more, a team of researchers retrospectively analyzed data from 182 MG patients and 324 people without the disease who underwent the Tensilon test at the Medical University of Vienna between 1991 and 2024. Those without the condition served as controls.
When the test was performed, about 60% of the patients had ocular MG and approximately 40% had generalized MG, when the disease affects several muscles throughout the body. Most patients (80%) had anti-AChR antibodies. Seven patients (4%) had antibodies against less common targets, including the anti-muscle-specific kinase (MuSK) protein, while 29 (16%) had no detectable self-reactive antibodies.
Data showed that the Tensilon test could distinguish between people with MG and those without with a sensitivity of 83.5%, and a specificity of 87.7%.
There were no significant differences in the test’s sensitivity related to the presence and type of self-reactive antibodies, age at disease onset, MG type, and treatment with pyridostigmine (sold as Mestinon, with generic available).
However, its sensitivity was significantly higher in patients with a decrease in nerve signals transmitted to muscles after RNS, a hallmark of MG, relative to those without such response (88.4% vs. 66.7%).
Still, the fact that about two-thirds of MG patients with a negative RNS result still had a positive Tensilon test highlights its potential as an adjunctive diagnostic test, according to the researchers.
Further statistical analysis indicated that MG patients with signal decrease after RNS were nearly four times more likely to respond to the Tensilon test. In contrast, patients with anti-MuSK antibodies were 92% less likely to have a positive Tensilon test compared with those with anti-AChR antibodies.
Overall, these results indicate that “combining RNS and the edrophonium test might therefore increase their diagnostic performance in patients with suspected MG while antibody results are pending,” the researchers wrote.
Adverse events seen for 1 in 10 patients given test
About 10% of all participants experienced adverse events with the test, which were generally mild to moderate in severity. The most commonly reported adverse events included vertigo, or a sensation of spinning, affecting slightly more than 3% of patients, and muscle cramps or twitches, experienced by nearly 3%. Eexcessive sweating was seen in slightly more than 2% of patients, as was lacrimation, or excessive tearing of the eyes, and nausea. No cases of breathing problems were observed.
One patient without known heart-related conditions developed a severely low heart rate, which rapidly reversed with appropriate treatment.
The researchers concluded that the Tensilon test may be useful as an adjunctive diagnostic tool, particularly in people with ocular MG, “where RNS has lower sensitivity” and in patients without known self-reactive antibodies, “as well as in cases where rapid information is needed to guide treatment decisions in severely affected patients.”
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