Specific muscle strength is reduced in facioscapulohumeral dystrophy: An MRI based musculoskeletal analysis

Abstract

The aim was to test whether strength per unit of muscle area (specific muscle strength) is affected in facioscapulohumeral dystrophy (FSHD) patients, as compared to healthy controls. Ten patients and ten healthy volunteers underwent an MRI examination and maximum voluntary isometric contraction measurements (MVICs) of the quadriceps muscles. Contractile muscle volume, as obtained from the MR images, was combined with the MVICs to calculate the physiological cross-sectional area (PCSA) and muscle strength using a musculoskeletal model. Subsequently, specific strength was calculated for each subject as muscle strength divided by total PCSA. FSHD patients had a reduced quadriceps muscle strength (median(1st quartile-3rd quartile): 2011 (905.4-2775) N vs. 5510 (4727-8321) N, p <0.001) and total PCSA (83.6 (62.3-124.8) cmvs. 140.1(97.1-189.9) cm, p = 0.015) compared to healthy controls. Furthermore, the specific strength of the quadriceps was significantly lower in patients compared to healthy controls (20.9 (14.7-24.0) N/cmvs. 41.9 (38.3-49.0) N/cm, p <0.001). Thus, even when correcting for atrophy and fatty infiltration, patients with FSHD generated less force per unit area of residual muscle tissue than healthy controls. Possible explanations include impaired force propagation due to fatty infiltration, reduced intrinsic force-generating capacity of the muscle fibers, or mitochondrial abnormalities leading to impaired energy metabolism.

Advancements in magnetic resonance imaging‐based biomarkers for muscular dystrophy

“…Several postprocessing methods that have been described in the muscular dystrophy literature share additional limitations. These methods usually rely on investigators to segment individual muscles or muscle groups by hand . This method is time‐consuming, and it requires detailed anatomical knowledge to define the muscles that are being examined.…”

“…These methods usually rely on investigators to segment individual muscles or muscle groups by hand. 33 This method is time-consuming, and it requires detailed anatomical knowledge to define the muscles that are being examined. One of the ways that investigators have sought to reduce the postprocessing time is to analyze only a subset of the collected data.…”

“…Analyzing potentially hundreds of slices by using manual selection of individual muscles is generally too time consuming to be performed in a clinical setting . In a research context, however, contractile muscle areas and volumes may serve as a relatively straightforward biomarker of overall muscle health …”

“…32 In a research context, however, contractile muscle areas and volumes may serve as a relatively straightforward biomarker of overall muscle health. [33][34][35]…”

Exploration of New Contrasts, Targets, and MR Imaging and Spectroscopy Techniques for Neuromuscular Disease – A Workshop Report of Working Group 3 of the Biomedicine and Molecular Biosciences COST Action BM1304 MYO-MRI

“…– other closely related measures, such as contractile cross-sectional-area (cCSA = % fat × total CSA) or muscle volume have also been widely investigated and it was shown that specific strength is reduced in a number of NMD [10, 203–205]. Recently, this analysis was extended by obtaining physiological cross-sectional areas in patients with FSHD, showing that specific strength is also reduced in these patients [206]. Besides the relation with function, some recent studies also focused on the methodological aspects of fat infiltration as outcome measure.…”