Clinic And Quantitative Skeletal Muscle MRI Study Of Children With Duchenne Muscular Dystrophy

Objective:1.To evaluate the frequency and degree of muscle fat infiltration and inflammatory edema of Duchenne muscular dystrophy(DMD)patients with MRI,and correlate these with clinical assessments.2.To discuss the value of HISTO-MRS in differentiating boys with DMD from healthy boys.3.To explore the value of quantitative magnetic resonance imaging(qMRI)in evaluating the progression of DMD by observing the longitudinal changes of scores of fat infiltration and fat fraction(FF)with T1WI and Dixon method befor and after follow-up.Materials and methods:1.Eighty-four boys confirmed with DMD by histopathology or genetic testing underwent thigh muscle MRI scans.Retrospective analysis was performed on the clinical data and the MRI findings.Clinical motor function scales was graded from I to Ⅳ.Axial T1-and fat suppressed T2-weighted images were adopted to grade muscle fat infiltration score from 0 to 4 and edema score from 0 to 3 respectively.Fat infiltration and inflammatory edema scores were performed in 13 thigh muscles of boys with DMD.2.Thirty-six age-matched healthy boys were recruited in this study.HISTO sequence was performed on the right gluteus maximus(GM),adductor magnus(AM),vastus lateralis(VL)and biceps femoris(BF)muscles in which the fat fractions(HISTO-FF)and MRS map of these muscles can be acquired automatically.3.Twenty-two patients with DMD were longitudinally followed up with twice thigh muscle MRI scans before and after.The quadriceps femoris,adductor magnus,gracillis and flexors were selected as the four target muscles.T1WI and Dixon were performed to observe the longitudinal changes of T1WI grade scores and fat fration(Dixon-FF)values.Results:1.Different degrees of fat infiltration with symmetrical distribution were present in the thigh muscles.The higher the frequency of fat infiltration,the greater the degree of muscle infiltration.Asymmetric distribution of edema was presented in bilateral thigh muscle.The edema frequency was significantly lower than fat infiltration.2.There was no significant difference in fat infiltration and inflammatory edema between DMD boys with different types of gene mutations.3.The cumulative score of fat infiltration was positively correlated with clinical motor function grades,age,height and weight;but did not have correlation with BMI and CK.Statistically significant correlation was not seen between score cumulative scores and any of the clinical evaluations.4.HISTO-FF was significant higher in the DMD group than the control group.The FF of youngest group was also higher than that of the healthy control group.The FF values at GM,AM,VL and BF of different age groups were significantly different.5.The FF values at GM,AM,VL and BF were strongly positively correlated with age,T1WI score of fat infiltration and the severity of clinical function.6.T1WI mean score and Dixon-FF mean values significantly increased in the quadriceps femorns,adductor magnus and flexors muscles in boys with DMD compared with those before follow-up.FF values of patients whose T1WI score did not change significantly could show differences.The patients with DMD might lose ambulatory function if the Dixon-FF value was greater than 60%in adductor magnus muscle.Conclusion:1.The MRI features of DMD were characterized by symmetrical fat infiltration in involved thigh muscles.The frequency of muscle inflammatory edema was lower than fat infiltration.There were no regular distribution pattern and severity regarding myoedema.2.MRI findings were not related to the type of gene mutation.T1WI can play important role on assessing the severity and progression of the disease.Myoedema was not found to be able to predict patients’ functional status.3.HISTO-MRS could be used to identify DMD boys from healthy boys,even in the younger age group.4.HISTO-FF was highly positively correlated with age.The higher the FF value,the higher the score of T1WI fat infiltration,and the worse the clinical motor function.5.Both T1WI and Dixon can be used to quantificationally measure logitudinal changes of fat infiltration in the thigh muscles of DMD boys.Dixon has higher sensitivity and accuracy in clinical follow-up and research.