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A Less Invasive Technique to Measure Extraocular Movement in Myasthenia Gravis

A novel technology for assessing eye movements may provide a less invasive alternative to repetitive nerve stimulation for diagnosing myasthenia gravis, a research team suggested in a presentation at the American Association of Neuromuscular & Electrodiagnostic Medicine 2020 Virtual Annual Meeting.

The scientists used videonystagmography (VNG)—video goggles with mini-cameras—to record voluntary eye movements in patients with myasthenia gravis and healthy controls. They found that patients with MG had a decrement in extraocular muscle activity compared with healthy controls.

The change was only a few seconds, but the scientists believe that the technology is accurate enough to help in the diagnosis of MG.        

"When we encounter patients with ptosis in the outpatient clinic, ocular MG is one of the diagnoses," said Goknur Kocak, MD, a neurology resident at the Istanbul University-Cerrahpasa Faculty of Medicine, who with colleagues at her institution collaborated with Andrea Corse, MD, associate professor of neurology and neurosurgery at Johns Hopkins University School of Medicine.

"However, sometimes we cannot find any evidence to support the diagnosis other than anamnesis. Ocular myasthenia gravis is characterized by ptosis and oculomotor paresis, but a technique to directly evaluate the extraocular movement activity hasn't been used. Developing a non-invasive tool led us to use VNG to record eye movement."

The research team recruited 13 patients with ocular MG and 21 with generalized MG as well as 23 healthy volunteers. All were asked to wear video goggles while the scientists recorded the velocity of their eye movements as they followed a moving target. They put visual targets in the horizontal planes so that the eye excursion of a person three feet away would be 20 degrees from the primary gaze (center gaze). All participants sat in an upright position three feet away from the visual display. The recording lasted for 60 seconds per eye, and the investigators administered the test to the two eyes separately.

Dr. Kocak told Neurology Today that she fixed the eyelids with medical tape to prevent ptosis that might occur during the test.                             

The MG patients showed significant eye muscle fatigue during the exercise, but the patients quickly recovered. By contrast, there was no decrement in fatigue in the healthy volunteers.

An increment response started within one to two seconds, which "is critically important for neuromuscular junction disorders," Dr. Kocak said, adding: "It was so similar to the so-called U-shaped decrement that is demonstrated in diagnostic repetitive nerve stimulation studies."

She said that VNG is used as a primary diagnostic tool for investigating the source of vestibular disorders such as vertigo and balance disturbances.               

"During the VNG assessment, the patient only wears goggles, which is more comfortable, and VNG is less operator-dependent compared with other tests, increasing test reliability. You can achieve a diagnosis in less time than other techniques as it takes one minute per eye to carry out the test." 

Dr. Kocak, whose abstract earned her the AANEM 2020 Golseth Young Investigator Award, said that this is the first study to utilize VNG to demonstrate extraocular movement activity indirectly. "Further research is necessary to confirm the diagnostic accuracy of VNG compared with currently used diagnostic tests," she said.

Robert L. Ruff, MD, PhD, FAAN, professor emeritus at Case Western Reserve University of Medicine, said that other studies have measured velocity of eye movements in MG patients and identified abnormalities unique to MG.

"What the researchers did that was new was to use easily available technology to record eye movements," said Dr. Ruff, who was not involved with the study. "They used current, inexpensive, and readily available technology to be able to detect abnormalities in eye movements associated with MG."

Dr. Ruff noted that the technology could be used without needing special labs or expensive equipment. The advance implements and applies available engineering technology to enable people to perform diagnostic noninvasive procedures, he said.

He added: "If I were a patient with MG, I would much prefer undergoing a video study of my eye movements rather than any form of EMG."

Drs. Kocak and Ruff had no relevant disclosures.

AANEM 2020 Abstract 1: Kocak G, Dolek B, Tutuncu M, et al. A novel diagnostic method for myasthenia gravis.