Relationship between markers of disease activity and progression in skeletal muscle of GNE myopathy patients using quantitative nuclear magnetic resonance imaging and (31)P nuclear magnetic resonance spectroscopy.

BACKGROUND: Quantitative nuclear magnetic resonance imaging (NMRI) is an objective and precise outcome measure for evaluating disease progression in neuromuscular disorders. We aimed to investigate predictive 'disease activity' NMR indices, including water T(2) and (31)P NMR spectroscopy (NMRS), and its relation to NMR markers of 'disease progression', such as the changes in fat fraction (ΔFat%) and contractile cross-sectional area (ΔcCSA), in GNE myopathy (GNEM) patients. METHODS: NMR was performed on a 3T clinical scanner, at baseline and at a 1-year interval, in 10 GNEM patients and 29 age-matched controls. Dixon-based fat-water imaging and water T(2) mapping were acquired in legs and thighs, and in the dominant forearm. (31)P NMRS was performed at the level of quadriceps and hamstring. Water T(2) and (31)P NMRS indices were determined for all muscle groups and visits. Correlations were performed with 'disease progression' indices ΔFat%, ΔcCSA and the muscle fat transformation rate (R(muscle_transf)). RESULTS: In quadriceps, known to be relatively preserved in GNEM, water T(2) at baseline was significantly higher compared to controls, and correlated strongly with the one-year evolution of Fat% and cCSA and R(muscle_transf). Various (31)P NMRS indices showed significant differences in quadriceps and hamstring compared to controls and correlations existed between these indices and ΔFat%, ΔcCSA and R(muscle_transf). CONCLUSIONS: This study demonstrates that disease activity indices such as water T(2) and (31)P NMRS may predict disease progression in skeletal muscles of GNEM patients, and suggests that these measures may be considered to be valuable surrogate endpoints in the assessment of GNEM disease progression.