The method used to quantify fat replacement in muscles to monitor disease progression in muscular disorders such as Pompe disease should be chosen based on the goal of the inquiry and the characteristics of the patients, concluded a study that compared different methods of analysis.
More precisely, an analysis by individual muscles seems to be more accurate in patients with moderate fat replacement or in transversal studies where the variable to study is the percentage of fat in muscle. Conversely, a global approach where compartments or the whole muscle is analyzed seems to be more accurate in patients with little fat replacement or in longitudinal studies where the variable of interest is the increment in the percentage of fat in muscle.
Quantitative MRI using the Dixon method has increasingly been used to measure disease progression in muscular disorders by measuring changes in muscle fat content. However, it can take a long time to analyze the images obtained.
In order to check if different approaches to the quantification showed differences in the increase of fat content and to identify which method of analysis better correlated with the results of muscle function tests, a team of researchers led by Jordi Díaz-Manera compared 3 methods of analysis of 2-point-Dixon images in 34 patients with late-onset Pompe disease (LOPD). The study was published online in Frontiers in Neurology.
The researchers measured the percentage of fat in the patients’ muscles (known as the fat fraction) at the start of the study and one year later and calculated the increment in fat fraction. They then correlated the results with the results of muscle function tests to see whether there were any differences between the 3 methods.
“We observed significant differences between the three methods in the estimation of the fat fraction at both baseline and year 1, but no difference was found in the increment in fat fraction between baseline and year 1,” the researchers wrote.
They also found a significant correlation between all 3 methods and muscle function with the highest correlation coefficient being obtained when individual muscles were analyzed.
“The fastest strategy of analysis assessing compartments or the whole thigh could be reliable for certain cohorts of patients where the variable to study is the fat increment,” the authors concluded. “In other sorts of studies, an individual muscle approach seems the most reliable technique.”
Alonso-Jiménez A, Nuñez-Peralta C, Montesinos P, et al. Different approaches to analyze muscle fat replacement with Dixon MRI in Pompe disease. Front Neurol. Published online Jul 8, 2021. doi:10.3389/fneur.2021.675781