Quantitative MRI and strength measurements in the assessment of muscle quality in Duchenne muscular dystrophy.

The purpose of this study was to assess leg muscle quality and give a detailed description of leg muscle involvement in a series of Duchenne muscular dystrophy patients using quantitative MRI and strength measurements. Fatty infiltration, as well as total and contractile (not fatty infiltrated) cross sectional areas of various leg muscles were determined in 16 Duchenne patients and 11 controls (aged 8-15). To determine specific muscle strength, four leg muscle groups (quadriceps femoris, hamstrings, anterior tibialis and triceps surae) were measured and related to the amount of contractile tissue. In patients, the quadriceps femoris showed decreased total and contractile cross sectional area, attributable to muscle atrophy. The total, but not the contractile, cross sectional area of the triceps surae was increased in patients, corresponding to hypertrophy. Specific strength decreased in all four muscle groups of Duchenne patients, indicating reduced muscle quality. This suggests that muscle hypertrophy and fatty infiltration are two distinct pathological processes, differing between muscle groups. Additionally, the quality of remaining muscle fibers is severely reduced in the legs of Duchenne patients. The combination of quantitative MRI and quantitative muscle testing could be a valuable outcome parameter in longitudinal studies and in the follow-up of therapeutic effects.

Intake of 13C-4 creatine enables simultaneous assessment of creatine and phosphocreatine pools in human skeletal muscle by 13C MR spectroscopy.

The feasibility of a novel method for the noninvasive and local assessment of creatine (Cr) and phosphocreatine (PCr) dynamics in human skeletal muscle based on (13)C magnetic resonance (MR) spectroscopy is presented. A high dose of Cr, labeled at the guanidino C-4 position with (13)C 11% enrichment, was administered orally to a human subject for 5 days. Using a surface coil, (13)C MR spectra of the lower leg were acquired on a 1.5T MR system at regular time intervals during and after Cr supplementation. An almost twofold increase in the intensities of the resolved PCr and Cr (13)C-4 signals was observed during this period. The slow decrease in these signals to normal values after supplementation reflects the slow daily turnover of Cr. The PCr/Cr ratio did not appear to change over the whole measurement period. During exercise of the leg, reversible changes in PCr and Cr signals were observed, reflecting conversion by the Cr kinase reaction.