Longitudinal measurements of MRI-T2 in boys with Duchenne muscular dystrophy: effects of age and disease progression

Abstract

Duchenne muscular dystrophy (DMD) is characterized by an increased muscle damage and progressive replacement of muscle by noncontractile tissue. Both of these pathological changes can lengthen the MRI transverse proton relaxation time (T2). The current study measured longitudinal changes in T2 and its distribution in the lower leg of 16 boys with DMD (5-13years, 15 ambulatory) and 15 healthy controls (5-13years). These muscles were chosen to allow extended longitudinal monitoring, due to their slow progression compared with proximal muscles in DMD. In the soleus muscle of boys with DMD, T2 and the percentage of pixels with an elevated T2 (⩾2SD above control mean T2) increased significantly over 1year and 2years, while the width of the T2 histogram increased over 2years. Changes in soleus T2 variables were significantly greater in 9-13years old compared with 5-8years old boys with DMD. Significant correlations between the change in all soleus T2 variables over 2years and the change in functional measures over 2years were found. MRI measurement of muscle T2 in boys with DMD is sensitive to disease progression and shows promise as a clinical outcome measure.

Keywords: 30 Foot walk; Duchenne muscular dystrophy; Magnetic resonance imaging; Transverse relaxation time.

Figure 1

Top: T₂-weighted images acquired in a boy with DMD (aged 9.9 years at baseline) over two years, showing increasing areas of hyperintensity over time. Bottom left: T2-weighted image from a 10 year old control boy, with homogeneous signal intensity in muscle. Bottom right: Longitudinal changes in the soleus T₂ histogram in the above subject, illustrating changes in the histogram with disease progression. The rightward shift is captured by the mean T₂ value, while the broadening of the histogram is captured by the FWHM and FWQM (dashed lines). The upper boundary of the T₂ of healthy muscle (defined as the 95th percentile of the control T₂ histogram) is represented by the vertical dotted line.

Figure 2

Individual mean soleus T₂ data plotted against age. For clarity, only baseline and 2 year points are shown. T₂ increased with time in boys with DMD at all ages, but changes were considerably more pronounced after approximately 9 years old. The boy diagnosed with BMD is shown in grey. Solid and dashed lines across the bottom of the plot represent the control mean and 95% confidence intervals.

Figure 3

Longitudinal changes in mean T₂ (A), elevated pixels (B), FWHM (C), and FWQM (D) in the soleus muscle. Solid horizontal line represents the control mean, while the dashed horizontal line represents the 95% confidence intervals around the control mean.

Figure 4

Longitudinal changes in mean T₂ in the peroneal, soleus, and tibialis anterior muscles.

Figure 5

Correlation between the change in T₂ variables in the soleus (over two years) and the change in 30 ft walk time (over two years). Two boys lost ambulation before or during the study, and were assigned an arbitrary maximum value to permit analysis using Spearman rank correlations. The two nonambulatory boys are represented by open circles.