A new, more sensitive method for diagnosing neuromuscular diseases

Researchers from Brazil and Sweden utilize single fiber electromyography to detect diseases affecting neuromuscular joints, such as myasthenia gravis

By Elton Alisson

Agência FAPESP – Patients who suspect that they may have a neuromuscular disease affecting neuromuscular junctions can now rely on a more sensitive detection technique in Brazil.

Researchers at the São José do Rio Preto Medical School (Famerp), in collaboration with scientists in Sweden, are utilizing single-fiber electromyography (SFEMG) to diagnose myasthenia gravis, a neuromuscular disease that causes rapidly progressing weakness in voluntary muscles and affects 10 to 20 individuals per million annually worldwide.

Developed at the end of 1960s by the neurophysiologist Erik Stålberg at Uppsala University, this very complex  technique has not been utilized in Brazil because of a lack of research specialization.

To learn this technique, Professor João Aris Kouyoumdjian of Famerp attended a specialization course in Uppsala, where he was mentored by Professor Stålberg, and initiated research into using the technique in Brazil.

In the past few years, through a research project funded by FAPESP, Famerp researchers have acquired equipment to begin conducting exams in patients with myasthenia gravis at the Medical School’s Base Hospital under the National Health System (SUS).

The results of the study conducted by Kouyoumdjian in collaboration with Stålberg were published in December in Muscle & Nerve . The group had previously published four other works concerning the utilization of this technique in healthy people to obtain baseline values.

“This work represents a landmark for Brazilian clinical neurophysiology. It is the first academic account of utilization of this technique in myasthenetics in the country,” Kouyoumdjian said in an interview.

He pointed out that the method is very efficient for diagnosing myasthenia gravis, as has been shown in other international studies, noting that  the method identified neuromuscular transmission abnormalities in 18 of 20 patients with the disease. “The sensitivity is almost 90%.”

In the study, the scientists utilized only disposable concentric needles, which are  thinner and safer than those typically employed for single-fiber electromyography. The electrode, which is inserted into a patient’s muscle, is capable of detecting isolated contractions of two close muscle fibers in the same motor unit, which are registered as action potentials on the equipment screen. The screen was acquired with FAPESP funding.

By comparing these registries, it is possible to measure variations in the duration of muscle-fiber contractions, known as jitters, which lasts a maximum of 35 to 40 microseconds, depending on the muscle analyzed, in individuals without the disease. In patients with neuromuscular transmission disorders such as myasthenia gravis, the jitter lasts longer: from 100 to 150 microseconds.

“In myasthenia gravis, the acetylcholine receptors that regulate contractions are partially blocked by antibodies in such a manner that synaptic transmission becomes slower, causing the symptoms,” Kouyoumdjian explained.

According to Kouyoumdjian, there are currently 80 patients with myasthenia gravis under the care of Famerp’s hospital. The treatment is conducted with medication that initially increases acetylcholine release in neuromuscular junctions (anticholinesterase pyridostigmine) and  subsequently increases immunosuppressive release.

Kouyoumdjian estimated that there are currently between 10 and 20 new cases in the São José do Rio Preto region alone. The disease primarily affects young women from 18 to 30 years of age and men around 50 years of age.

The primary symptom of myasthenia gravis is weakness that oscillates during the day. Patients tend to wake up well during the morning but, as the day progresses, feel weak, showing asymmetrical droops in the eyebrows, diplopia (double vision), and difficulty extending their arms or climbing stairs.

The article by Kouyoumdjian and Stålberg, “Concentric needle jitter on stimulated frontalis and extensor digitorium in 20 myasthenia gravis patients,”  can be read by subscribers of Muscle & Nerve at onlinelibrary.wiley.com/doi/10.1002/mus.22203/abstract.