Optically pumped magnetometer magnetomyography (OPM-MMG) can record pathological voluntary muscle activity, and contactless recording might be of value to patients with conditions like Pompe disease (PD) that require periodic recordings for therapeutic monitoring, according to a recently published study in Frontiers Neuroscience

Electromyography (EMG) is currently the gold standard for measuring electrophysiological changes in neuromuscular diseases. Although EMG has proven to be a reliable technique, many patients consider it uncomfortable or painful, and it is impossible to perform in many children. 

OPM-MMG can measure the magnetic fields produced by the flow of electrical current in the muscles and, unlike EMG, does not require contact with skin surfaces. Although evidence suggests OPM-MMG could be more representative of muscle activity than traditional EMG, most available studies focus only on its capacity to measure physiological muscle activity.


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“To demonstrate for the first time that OPM-MMG is capable of being a new modality for clinical application, we performed a proof-of-principle study on 3 patients with neuromuscular disease performing an isometric contraction of the left rectus femoris muscle,” the authors wrote. 

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The 3 patients included in the study had myotonica congenita (MC), transthyretin amyloidosis (ATTR) in combination with PD, and Charcot-Marie-Tooth disease, type 2 (CMT2). The patient with MC had no clinical or electrophysiological signs of neurogenic muscle damage and practically served as a control patient together with 7 healthy controls.

Comparison between patients with neuromuscular disease and healthy controls revealed a reduced variability of the MMG signal, indicative of the loss of motor neurons and decreased possibility of motor unit recruitment in these patients. Furthermore, patients with neuromuscular disease had dispersed interference alongside high amplitudes that were not present in healthy controls- Results were confirmed using simultaneous surface electromyography EMG.

“In this proof-of-principle study, we introduced OPM-MMG as a noninvasive method to detect neurogenic muscle damage in patients,” the authors concluded.

Reference

Semeia L, Middelmann T, Baek S, et al. Optically pumped magnetometers detect altered maximal muscle activity in neuromuscular disease. Front Neurosci. Published online November 29, 2022. doi:10.3389/fnins.2022.1010242