DUCHENNE MUSCULAR DYSTROPHY – IMAGING AND BIOMARKERS: P.37Upper extremity quantitative muscle ultrasound is related to disease severity in boys with Duchenne muscular dystrophy

Abstract

With an increasing amount of non-ambulant boys with Duchenne muscular dystrophy (DMD), objective and child-friendly outcome measures are necessary to evaluate upper limb function in boys with DMD. The primary aim of this study was to assess the relation between upper extremity quantitative muscle ultrasound (QMUS) and disease severity in boys with DMD. Additionally, reference values of QMUS were collected in healthy boys and the effect of age on QMUS was compared between healthy boys and boys with DMD. Finally, reliability was assessed in a subgroup of both groups (12 healthy boys and 10 boys with DMD). Echo intensity (EI) and muscle thickness (MT) of the upper limb measured by QMUS were determined in 71 healthy boys and 43 boys with DMD (mean age 12.45 and 12.41 years). Clinical assessments (upper extremity muscle strength (MS), Brooke scale, Performance of upper limb (PUL) and Motor Function Measure Dimension 3 (MFM-D3)) were performed in boys with DMD only. The effect of age on QMUS was assessed using linear regression analysis. The relation between QMUS and clinical assessments was assessed using correlation coefficients. ICC's were constructed to determine inter-rater and test-retest reliability. EI was higher and increased with age in boys with DMD whereas in healthy boys EI was independent of age. MT increased with age in healthy boys whereas age did not influence MT in boys with DMD. A higher EI was related to decreased performance on Brooke scale, PUL and MS of shoulder abductors. A lower MT was related to decreased performance on Brooke scale and MS of shoulder abductors. This study found excellent inter-rater reliability of EI in healthy boys, which is in accordance with previous literature. Poor test-retest reliability of EI was found in both healthy boys and boys with DMD. QMUS of the upper extremity is related to disease severity in boys with DMD. Therefore, this study establishes QMUS of the upper extremity as an objective, relevant outcome measure in DMD which is not influenced by fatigue, verbal understanding or patient cooperation.