Skeletal Muscle Ultrasound: Correlation Between Fibrous Tissue and Echo Intensity

doi:10.1016/j.ultrasmedbio.2008.09.016

Ultrasound in Medicine & Biology

Volume 35, Issue 3, March 2009, Pages 443-446

https://doi.org/10.1016/j.ultrasmedbio.2008.09.016 Get rights and content

Abstract

In this study, we examined the correlation between muscle ultrasound and muscle structure. Echo intensity (EI) of 14 muscles of two golden retriever muscular dystrophy dogs was correlated to the percentage interstitial fibrous tissue and fat in muscle biopsy. A significant correlation between interstitial fibrous tissue and EI was found (r = 0.87; p < 0.001). The separate influence of interstitial fat on muscle EI could not be established as only little fat was present. We conclude that fibrous tissue causes increased muscle EI. The high correlation between interstitial fibrous tissue and EI makes ultrasound a reliable method to determine severity of structural muscle changes. (E-mail: [email protected])

Introduction

Muscle ultrasound is an easy applicable diagnostic tool in the evaluation of neuromuscular disorders (Heckmatt et al 1988, Pillen et al 2007, Reimers and Kellner 1996, Walker et al 2004). The main muscle ultrasound finding in many neuromuscular disorders is increased muscle echo intensity, which is said to be caused by the disruption of normal muscle architecture by infiltration of fat and fibrous tissue (Heckmatt et al 1982, Reimers and Kellner 1996, Walker et al 2004). As muscle ultrasound is used for the diagnostic evaluation of neuromuscular disorders, it is important to know the influence of different types of muscle pathology on muscle echo intensity. This knowledge can aid in the interpretation of muscle ultrasound results when used for the detection of neuromuscular disorders or determination of muscle biopsy location. Until now, only two studies have examined the correlation between muscle biopsy findings and muscle echo intensity (Reimers et al 1993, Reimers et al 1993). A significant correlation was found between the amount of interstitial fat and muscle echo intensity. It was not possible to determine the influence of fibrous tissue alone on muscle echo intensity because the percentage fibrous tissue in the muscle specimens of these studies was either low (Reimers et al. 1993b) or strongly correlated to the amount of fat (Reimers et al. 1993a).

In the present study, we aimed to determine the influence of fibrosis on muscle echo intensity. The muscles under investigation had to contain a variable amount of fibrosis and only a small amount of interstitial fat to be able to separately assess the influence of fibrosis. We, therefore, chose to perform this study in golden retriever dogs suffering from muscular dystrophy (GRMD) (Cooper et al 1988, Valentine et al 1992). GRMD dogs show prominent necrosis and regeneration in muscle biopsies, with marked fiber size variation and fibrosis and, in dogs over 1 y of age, fibrosis was more prominent than fat infiltration (Valentine et al. 1990). As the muscle specimens were obtained post mortem, it was possible to examine complete muscle cross-sectional areas to avoid sampling error.

Section snippets

Methods

Ultrasound measurements of 14 muscles were made in two GRMD dogs aged 27 (dog 1) and 20 months (dog 2) with end-stage cardiomyopathy. The dogs were born from a carrier dam that was inseminated with semen of an affected male GRMD dog. The dam and the semen were obtained from a GRMD colony at the University of Missouri. The study was approved by our institutional animal care and use committee. The following muscles were measured: rectus femoris, adductor magnus, sartorius, tibialis anterior,

Results

Histologic examination of the muscles revealed only small amounts of fat (median 1.5%; range 0% to 11%;). The percentage fibrous tissue varied from 5% to 38% (median 13%). The second dog showed less fibrosis than the first dog, which can be explained by his younger age. Echo intensity ranged from 13 to 55 (median 23). The highest echo intensities were found in the sartorius and rectus femoris muscle, the lowest echo intensities in the deltoid and adductor magnus muscles. Examples of the

Discussion

Previous studies have already shown a strong correlation between muscle biopsy findings and muscle echo intensity (Heckmatt et al 1982, Reimers et al 1993, Reimers et al 1993). Especially, the infiltration of fat was held responsible for an increase of reflective interfaces resulting in higher echo intensities (Reimers et al. 1993b). The present study shows that fibrous tissue also leads to increased muscle echo intensity. Both findings combined again indicate that muscle ultrasound is a

Acknowledgments

The authors thank the University of Missouri for providing the GRMD carrier dam and semen and Nens van Alfen, MD, PhD, for her critical reading of the manuscript. The study was supported by a grant from the Prinses Beatrix Fonds (No. MAR02–0105) and a grant form The Netherlands Organization for Health Research and Development (ZonMw No. 907 to 00–057).

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Original contributionSkeletal Muscle Ultrasound: Correlation Between Fibrous Tissue and Echo Intensity

Abstract

Introduction

Section snippets

Methods

Results

Discussion

Acknowledgments

J Pediatr

Neuromuscul Disord

J Neurol Sci

J Neurol Sci

Ultrasound Med Biol

Clin Neurophysiol

Original contribution
Skeletal Muscle Ultrasound: Correlation Between Fibrous Tissue and Echo Intensity