Muscle strength and function measurements in people with late-onset Pompe disease (LOPD) correlate with whole-body magnetic resonance imaging (WBMRI) results, a new study suggests.
The study, “Whole‐body MRI in Late‐onset Pompe Disease: Clinical utility and correlation with functional measures,” was published in the Journal of Inherited Metabolic Disease.
WBMRI is an imaging technique that, among other things, allows for the assessment of body fat — specifically a measurement called proton-density fat-fraction (PDFF). A previous study, with a relatively small sample size (34 participants), showed that measurements taken via MRI correlated with muscle strength in people with LOPD, which is Pompe disease that develops anytime after the first year of life.
“Whole-body muscle MRI (WBMRI) has clinical utility in diagnosis and disease monitoring in LOPD,” the authors wrote. “However, WBMRI is costly, requires expertise to interpret, and may not be readily available at all centers. Muscle strength and functional testing are alternative, non-invasive means of evaluating muscle disease in LOPD patients and have been shown to correlate well with degree of fatty changes seen on imaging,” they stated.
In this study, researchers tried to see how muscle strength and functional measurements, namely Gait, Stairs, Gowers, Chair (GSGC) scores and the modified Medical Research Council (mMRC) scale, correlated to WBMRI findings.
The researchers assessed 19 people with LOPD (eight male, 11 female) who underwent tests of muscle strength, as well as WBMRI. Most of the participants (15) underwent at least two WBMRI scans, with one-year gaps between scans.
All participants underwent functional (i.e., muscle strength-related) assessment, most within a month of a WBMRI scan. Researchers measured muscle strength with the mMRC scale and also performed lab tests, including urinary glucose tetrasaccharide (Glc4).
The researchers then looked for statistical associations between PDFF, as measured by WBMRI, and these functional outcomes.
They found that both GSGC and mMRC scores correlated closely with PDFF measurements; the two functional assessments also correlated well with each other. Glc4 scores were normal, despite different degrees of muscle weakness in patients.
Based on this, the researchers suggested that assessing one of these metrics in an individual should give a pretty good indication of what the results will be for the other metrics. They pointed out that this means the functional tests, which are relatively easy to carry out, could be used to provide insight into the likely results from WBMRI, without having to do the costly and expertise-heavy scan itself.
The researchers also found that PDFF scores significantly correlated with the participants’ age when they were diagnosed with Pompe disease.
They did not find statistically significant changes in PDFF measurements over time, and there was no significantly different PDFF among participants who started treatment within a year of being diagnosed, and those who started treatment more than a year after being diagnosed.
The researchers acknowledged this study had limitations, particularly its small sample size and short follow-up period. They further noted that, “[O]ur data is not generalizable to all LOPD patients; patients requiring ventilatory support or those with severe disease who could not lie flat for the duration of the scan were excluded.”
“We demonstrate that GSGC correlates highly with fatty infiltration on WBMRI and suggest that it may be used during patient follow-up,” they concluded.