Quantitative MRI Measurements Can Distinguish Myositis From Healthy Control Muscle
Authors: Farrow Matt , Biglands John , Emery Paul , Buch Maya , Tanner Steve , Tan Ai Lyn 
Published: June 2021

IntroductionMyositis is an autoimmune inflammatory muscle disease which can decrease quality of life and increase mortality. Clinical presentation includes muscle weakness, changes in muscle microstructure, myosteatosis, raised muscle enzymes and myalgia. Currently, diagnosis is reliant on subjective clinical examinations, blood tests, and invasive muscle biopsies. Quantitative MRI techniques such as Diffusion imaging and Fat Fraction (FF) offer non‐invasive measurements, which could help the management and diagnosis of myositis. Diffusion measurements are sensitive to changes in muscle microstructure (1). FF provides a quantitative measure of myosteatosis in muscles (2). As well as collecting data on muscle architecture and myosteatosis using MRI techniques, to get a complete understanding of muscle health, it is beneficial to conduct quantitative muscle tests to understand the functional capability and how this compares with the MRI data. The aim of this study was to investigate whether fat fraction and mean diffusivity measurements in the thigh are sensitive enough to identify differences in myositis patients compared to healthy controls.Methods10 myositis patients (mean age 55 ± 18, 6 female) and 16 healthy controls (mean age 44 ± 17, 10 female), were enrolled in the study. Mean measurements of fat fraction (FF) and mean diffusivity (MD) were made using the 2‐point Dixon technique with a 3D gradient echo (VIBE) readout and a STEAM‐EPI sequence respectively. Mean values were obtained from the individual muscles that make up the quadriceps and hamstrings on the middle slice of the in‐phase VIBE Dixon volume (Figure 1). No distinction was made between affected and unaffected muscles. In addition to MRI, all participants had knee extension and flexion power and torque measured on an isokinetic dynamometer and handgrip measurements on an isometric dynamometer. Differences were assessed using independent T‐tests.Section 3: ResultsFF and MD were significantly higher in myositis patients compared to healthy controls, whereas muscle strength and power were significantly reduced (table 2 and figure 2).Section 4: Discussion and ConclusionMRI based FF and diffusion measurements can detect differences in the muscle between myositis patients and healthy controls with significant increases in both fat fraction and mean diffusivity, whilst concurrently muscle strength and power is significantly reduced, suggesting that they are related. The FF and MD may be raised due to the increased fluid content and a decrease in muscle fiber structure as a result of inflammatory changes occurring in the muscle. This is consistent with the known increase in myosteatosis, edema and the effects of muscle fiber plasticity seen within myositis patients. This study provides evidence that these measures may have potential as novel imaging biomarkers in the diagnosis and management of myositis.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.