Literature Review

Surface Electromyography May Detect Generalized Tonic-Clonic Seizures

Proper device positioning improves accuracy, but some patients may have an excessive number of false alarms.


 

A wearable surface electromyographic (sEMG) monitoring device may help to detect generalized tonic-clonic seizures (GTCS), according to research published in the November 2017 issue of Epilepsia. The monitoring system provides timely detection of GTCS within an average of 7.7 seconds of the onset of bilateral appendicular tonic motor manifestations.

“Since GTCS can cause patient injury and are associated with SUDEP, the [wearable] device should be useful to provide a method for caretakers to check on patient safety shortly after a GTCS,” said Jonathan J. Halford, MD, Associate Professor of Neurology at the Medical University of South Carolina in Charleston.

Jonathan J. Halford, MD

The prevalence of active epilepsy is between 0.4% and 1% worldwide. The prevalence of patients with frequent GTCS is unknown, but is estimated at between 10% and 20% of patients with active epilepsy. These patients have the highest risk for injuries, sudden unexpected death in epilepsy (SUDEP), and mortality from any cause. Early detection of GTCS and intervention may help to decrease morbidity and mortality, cases of status epilepticus, and SUDEP.

Evaluating Device Performance and Tolerability

A previous single-site study of an sEMG detection algorithm in an epilepsy monitoring unit detected 95% of 20 GTCS recorded in 11 epilepsy patients with one false positive. To evaluate the performance and tolerability in the epilepsy monitoring unit of an investigational wearable sEMG monitoring system for the detection of GTCS, Dr. Halford and colleagues conducted a prospective, multicenter phase III trial.

One hundred ninety-nine participants ranging in age from 3 to 72 with a history of GTCS (either primary GTCS or partial onset seizures with secondary generalization) and an upper-arm circumference adequate for proper fit of the device were included in the study. Participants had been admitted to an epilepsy monitoring unit for standard clinical care.

Researchers used a custom-designed device to record sEMG data. Recording electrodes were placed transversely over the belly of the biceps brachii muscle. The reference electrode was positioned proximally. The device was taken off and replaced every 12 hours during battery changes. In addition, patients were questioned once daily about adverse events, and skin in contact with the device was examined. Recorded sEMG data were processed at a central site using a previously developed detection algorithm. Finally, detected GTCS were compared with events confirmed by three expert reviewers.

Device Detected Most GTCS

For all participants, the detection algorithm detected 35 of 46 GTCS (ie, 76%), with a positive predictive value of 0.03 and a mean false alarm rate of 2.52 per 24 hours. When the device was placed over the midline of the biceps, the system detected 29 of 29 GTCS with a detection delay average of 7.70 seconds, a positive predictive value of 6.2%, and a mean false alarm rate of 1.44 per 24 hours.

When the device was placed between the biceps and triceps, it caused in-phase cancellation, significantly weakening the sEMG signal. After this discovery, all staff at all study sites were retrained to place the device over the midline biceps. Sixty-four percent of false alarms occurred during activity, and 62% of false alarms contained signal artifact commonly associated with loose electrodes, said the researchers.

Adverse Events and Study Limitations

Mild to moderate adverse events were reported in 28% of participants and led to withdrawal in 9%. Most adverse events consisted of skin irritation from the electrode patch (eg, skin tears, general discomfort, blisters, and bruising). No serious adverse events were reported.

In all, 23% of respondents said that the device was uncomfortable to sleep with. Forty-two percent of these participants reported that they would ask their physician to prescribe the system, and 26% reported that they would not. Thirteen percent of respondents had no opinion, and 18% did not comment.

One study limitation was the initially improper placement of the device. Furthermore, although this study shows that this system works in the epilepsy monitoring unit, it is unclear whether this device will work in the home environment.

In future research, Dr. Halford intends to study the sEMG signal from the scalp, recorded as part of standard EEG, to determine whether it could be used to detect GTCS during ambulatory or inpatient monitoring. He also plans to investigate ways to improve the tolerability of the sEMG monitoring device.

—Erica Tricarico

Suggested Reading

Halford JJ, Sperling MR, Nair DR, et al. Detection of generalized tonic-clonic seizures using surface electromyographic monitoring. Epilepsia. 2017;58(11):1861-1869.

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