US researchers discovered that quantitative muscle ultrasonography (QMUS) and electrical impedance myography (EIM) were reliable biomarkers of muscle structure and conduction properties in patients with late-onset Pompe disease (LOPD), according to a study published in Molecular Genetics and Metabolism Reports. 

LOPD leads to an abnormal accumulation of glycogen within body tissues, such as the muscles and the liver. The presentation of Pompe disease varies according to age, and diagnosis remains a challenge due to its vague presentation (typically respiratory insufficiency and proximal limb weakness). However, once diagnosed, enzyme replacement therapy (ERT) can vastly improve clinical outcomes. 

The next piece of the puzzle is finding the best way to track muscle health. Muscle biopsies are invasive, painful, and sometimes unreliable. Whole-body muscle magnetic resonance imaging (MRI) scans are costly and can be difficult to perform in patients with respiratory weakness. Hence, 2 noninvasive techniques to monitor disease progression have been proposed: QMUS and EIM. 

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Researchers sought to determine their efficacies by recruiting 32 patients diagnosed with Pompe disease who were receiving continuous treatment at the Duke Pompe Clinic in Durham, North Carolina. QMUS was performed at baseline, 12 months, and 24 months. EIM using standard equipment (sEIM) was performed in a clinical setting at 12 and 24 months, while EIM using a handheld device (hEIM) was performed by the participants at home once a week for 6 weeks.

The results showed that QMUS and hEIM had high inter-rater reliability, making them promising tools for the measurement of muscle health and disease progression. Furthermore, sEIM and hEIM measurements did not differ significantly, meaning that patients can potentially monitor their own muscle health at home using handheld EIM devices. Throughout the study period, measures did not change except for the increased echointensity of the vastus lateralis by 27%, signaling a worsening of muscle health. 

A limitation of this study was that the coronavirus disease 2019 (COVID-19) pandemic forced the study to be concluded prematurely. In April 2020, 8 patients were scheduled to have their last yearly visits, which were canceled due to pandemic restrictions. Due to the uncertain nature of the pandemic, a decision was made to wrap up the study and begin data analysis, possibly affecting the ability of researchers to better detect changes in QMUS and EIM measures over time.


Hobson-Webb LD, Zwelling PJ, Raja SS, Pifer AN, Kishnani PS. Quantitative muscle ultrasound and electrical impedance myography in late onset Pompe disease: a pilot study of reliability, longitudinal change and correlation with function. Mol Genet Metab Rep. Published online July 30, 2021. doi:10.1016/j.ymgmr.2021.100785