Swallowing Muscle Test May Help Diagnose MG

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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The flexible endoscopic evaluation of swallowing-tensilon test (FTT), a new diagnostic tool for myasthenia gravis (MG), can be used to distinguish people with swallowing difficulties due to MG from those having similar symptoms caused by other conditions, according to a new study.

The study, “Detecting myasthenia gravis as a cause of unclear dysphagia with an endoscopic tensilon test,” was published in the journal Therapeutic Advances in Neurological Disorders.

As many as two-thirds of people with MG will experience dysphagia, or difficulty swallowing, as a symptom of their condition. However, diagnosing MG can be difficult when dysphagia is the primary — or only —  symptom.

A classic test used to diagnose MG is the edrophonium test, though it is no longer used in the U.S. It involves administering edrophonium chloride to see if it leads to an improvement in muscle strength.

Edrophonium prevents the breakdown and increases the levels of acetylcholine, a signaling molecule that plays a key role in muscle contraction and whose receptors often are impaired in MG. As such, a temporary increase in muscle strength following edrophonium administration might indicate the presence of MG.

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Performing the edrophonium test in someone whose main symptom is dysphagia is complicated, however, since it is difficult for a person to feel whether the muscles used for swallowing are any stronger.

FTT basically involves using an endoscope — a flexible tube with a camera at the end — to observe the muscles in the throat while a person is swallowing, with or without edrophonium. Essentially, the goal is to perform a version of the edrophonium test that specifically focuses on the muscles that are impaired in people with dysphagia.

Now, a team led by researchers in Germany set out to determine whether FTT could be used to distinguish people with dysphagia due to MG from those with swallowing difficulties for other reasons.

In total, 100 people with dysphagia of unknown origin underwent FTT. The test was administered without any noteworthy problems or complications, according to scientists.

After FTT, patients underwent a battery of additional diagnostic tests. These tests revealed that 51 patients had MG; the rest ultimately were diagnosed with other conditions. About two-thirds of patients in the MG and non-MG groups were male, with a mean age in the early 60s.

In the FTT assessment, 88.2% of patients ultimately diagnosed with MG showed an improvement in swallowing muscle function after the administration of edrophonium. By contrast, only 4.1% of patients in the non-MG group experienced an improvement following edrophonium administration.

Based on these data, researchers concluded that FTT had a sensitivity (ability to detect true-positive cases) of 88.2%, and a specificity (ability to identify true-negative cases) of 95.9% for distinguishing MG from other conditions that also can cause dysphagia.

Notably, the FTT showed similar diagnostic accuracy as testing for the presence of autoantibodies — the self-reactive antibodies that cause MG — in the bloodstream, and it outperformed another diagnostic test called repetitive nerve stimulation, which evaluates a nerve’s ability to send a signal to a muscle.

“The results of this study indicate that the FTT is a useful tool to diagnose MG in patients with unclear dysphagia,” the researchers wrote.

In addition to its accuracy for diagnosis, researchers noted that FTT can be completed more quickly than some other tests, offering yet another advantage. For instance, antibody testing usually requires sending a blood sample to a lab for analysis, which can take days or weeks.

“In contrast, the FTT provides immediate results also at an early disease stage and can facilitate urgent therapy decisions while other diagnostics are pending,” the team wrote.

A noted limitation of this study is that, because the team was specifically looking at people whose main symptom was dysphagia, FTT’s potential usefulness in diagnosing MG in people with different predominant symptoms remains unclear. Investigators also noted that FTT requires expertise to perform and interpret properly, which could limit its use.