Quantitative ultrasound using backscatter analysis in Duchenne and Becker muscular dystrophy

Abstract

Evaluation of ultrasound images of muscle with calibrated muscle backscatter (cMB) provides reproducible quantitative measurements of muscle pathology. Increased cMB is associated with greater muscle pathology. We used cMB to evaluate the severity of muscle pathology in 55 patients with Duchenne and Becker Muscular Dystrophy (D/BMD) compared to 77 controls. cMB was also compared to measurements of strength and function. cMB in DMD and BMD increased linearly with age and was higher than in controls when groups are compared. cMB increased twice as fast with age in DMD than in BMD. In DMD, cMB was higher with reduced function and strength. Ultrasound measurement of muscle pathology using cMB is a sensitive and objective quantitative technique for determining the severity of muscle pathology in dystrophinopathies. Longitudinal studies are required to determine the sensitivity of this measure to changes in pathology over time.

Figure 1. Ultrasound Images of the Elbow Flexors in DMD and Control Subjects

Longitudinal ultrasound images of the elbow flexors are shown in DMD boys, ages A: 1.5 years, cMB 3.0dB, B: 8 years, cMB 10.1 dB, and C: 15 years 15.7 dB. An 8 year old control is shown in D: cMB −1.8 dB with the region of interest outlined in the muscle (m) between the subcutaneous fat (sc) and bone (b).

Figure 2. cMB in the Elbow Flexors in DMD Boys and Controls

In DMD boys, cMB in the extended arm increases linearly with greater age. In controls, the increase with age is more gradual. When comparing groups of subjects with controls, the difference between DMD and controls is detectable even for the 5 years and younger group (p < 0.01) and increases with greater age.

Figure 3. cMB in the Elbow Flexors Differentiates Boys with Duchenne from Becker Muscular Dystrophy

cMB of the elbow flexors was higher in boys with DMD (solid line) than BMD (dashed line, p<0.001), after accounting for age and age*diagnosis. cMB increased approximately 0.8 dB/year in DMD and 0.4 dB/year in BMD boys (age < 20 years). The mean (SD) cMB of the elbow flexors in adult men ages 35-47 years, four with BMD and seven healthy controls, is also shown.

Figure 4. Ultrasound cMB in DMD Patients: Relations to Function and Strength

In DMD patients cMB in the elbow flexors was greater with less upper extremity function (r_s=0.6, p=0.02) and weaker elbow flexor strength (MRC) (r_s = −0.4, p=0.03). There is a wide range of cMB levels in patients with similar levels of strength or function. The maximal value seen in child controls was 7.3 dB (dotted line).