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The role of novel motor unit magnetic resonance imaging to investigate motor unit activity in ageing skeletal muscle

Lookup NU author(s): Matt Birkbeck, Professor Andrew Blamire, Professor Roger Whittaker, Professor Avan Sayer, Dr Richard Dodds

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

Background Sarcopenia is a progressive and generalised disease, more common in older adults which manifests as a loss of muscle strength and mass. The pathophysiology of sarcopenia is still poorly understood with many mechanisms suggested. Age associated changes to the neuromuscular architecture, including motor units and their constituent muscle fibres, represent one such mechanism. Electromyography can be used to distinguish between different myopathies and produce counts of motor units. Evidence from electromyography studies suggests that with age, there is a loss of motor units, increases to the sizes of remaining units and changes to their activity patterns. However, EMG is invasive, can be uncomfortable, does not reveal the exact spatial position of motor units within muscle and is difficult to perform in deep muscles. Methods and Results We present a novel diffusion weighted magnetic resonance imaging (DW-MRI) technique called “Motor Unit Magnetic Resonance Imaging (MUMRI)”. MUMRI aims to improve our understanding of the changes to the neuromuscular system associated with ageing and sarcopenia. To date we have demonstrated that: MUMRI can be used to detect statistically significant differences in fasciculation rate of motor units between (n = 4) patients with Amyotrophic Lateral Sclerosis (mean age ± SD: 53 ± 15) and a group of (n = 4) healthy controls (38 ± 7). Patients had significantly higher rates of fasciculation compared with healthy controls (mean = 99.1/min, range = 25.7–161.0 in patients vs 7.7/min, range = 4.3–9.7 in controls; p < 0.05.MUMRI has detected differences in size, shape and distribution of single human motor units between (n = 5) young healthy volunteers (29 ± 2.2) and (n = 5) healthy older volunteers (65.6 ± 14.8). The maximum size of motor unit territories in the older group was (12.4 ± 3.3 mm and 9.7 ± 2.7 mm in the young group; p < 0.05. Conclusions MUMRI is an entirely non-invasive tool which can be used to detect physiological & pathological changes to motor units in neuromuscular diseases. MUMRI also has the potential to be used as an intermediate outcome measure in sarcopenia trials.


Publication metadata

Author(s): Birkbeck MG, Blamire AM, Whittaker RG, Sayer AA, Dodds RM

Publication type: Article

Publication status: Published

Journal: Journal of Cachexia, Sarcopenia and Muscle

Year: 2020

Pages: epub ahead of print

Online publication date: 22/12/2020

Acceptance date: 05/11/2020

Date deposited: 06/11/2020

ISSN (print): 2190-5991

ISSN (electronic): 2190-6009

Publisher: Wiley

URL: https://doi.org/10.1002/jcsm.12655

DOI: 10.1002/jcsm.12655


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