P.17.7 Quantitative NMR imaging of lower limb musculature in type II glycogenosis patients: Preliminary analysis of a 4-year follow-up

Skeletal muscle NMR imaging has two distinct roles: 1/ to diagnose disorders and 2/ to monitor disease progression. Both have been played to the benefit of type II glycogenosis patients (GSDII). In this study, we quantified muscle water T2, a marker of disease activity, in thigh and leg muscles of GSDII. We also investigated the relationship between T2 and the extension and progression of fatty degenerative changes in skeletal muscle. The degree of fatty infiltration in 11 thigh and 8 leg muscle heads was calculated for both lower limbs from a 3-point 3D Dixon acquisition. Since quantitative imaging has become standard in our department for the routine follow-up of GSDII in 2009, 36 patients have been examined, 17 were rescanned after 1 yr and 6 rescanned after 2 yrs. Twenty-one patients were treated by enzyme substitution, 2 stopped treatment during the observation. Quite a large number of muscles had abnormally elevated muscle water T2 (>39 ms): 84/296 in the thighs and 62/253 in the legs. Abnormal muscle water T2s were associated with higher percentages of fatty infiltration at 1 yr follow up: in the thighs: 11.6% vs 5.8% in normal T2 muscles, p < 0.0001; in the legs: 6.6% vs 4.9% in normal T2 muscles, p = 0.001. Treated patients had higher muscle T2s and fat fractions, which likely reflects the decision to treat the more severe cases in this open-label cohort, as indicated by the higher Mercuri score in the treated group. This study demonstrated the ability of quantitative NMR imaging to identify muscles with active disease in GSDII, and identified a link between disease activity and muscle fatty degenerative change severity.