Relationships of thigh muscle contractile and non-contractile tissue with function, strength, and age in boys with Duchenne muscular dystrophy

Abstract

The purpose of this study was to assess the contractile and non-contractile content in thigh muscles of patients with Duchenne muscular dystrophy (DMD) and determine the relationship with functional abilities. Magnetic resonance images of the thigh were acquired in 28 boys with DMD and 10 unaffected boys. Muscle strength, timed functional tests, and the Brookes Lower Extremity scale were also assessed. Non-contractile content in the DMD group was significantly greater than in the control group for six muscles, including rectus femoris, biceps femoris-long head and adductor magnus. Non-contractile content in the total thigh musculature assessed by MRI correlated with the Brookes scale (r(s)=0.75) and supine-up test (r(s)=0.68), as well as other functional measures. An age-related specific torque increase was observed in the control group (r(s)=0.96), but not the DMD (r(s)=0.06). These findings demonstrate that MRI measures of contractile and non-contractile content can provide important information about disease progression in DMD.

Figure 1

Representative T1-weighted 3-D gradient-echo magnetic resonance images (TR/TE, 24/1.8) of the mid-thigh for 14-year-old boy with DMD (A and C) and 12-year-old healthy boy (B and D). RF, rectus femoris; VL, vastus lateralis; VI, vastus intermedius, VM, vastus medialis, BFs, biceps femoris-short head; BFl, biceps femoris-long head; ST, semitendinosus; SM, semimenbronosus; AM, adductor magnus; AL, adductor longus; Gr, gracilis; Sar, sartorius Scale=5 cm

Figure 2

Method for determining non-contractile and contractile contents in the muscles of boys with DMD (B and D) and control (A and C). A and B: outline of region of interests (ROIs) on the sartorious (Sar) and gracilis (Gr) muscles (white) consisting of approximately 50% of muscle and subcutaneous fat and on the biceps femoris-long head (red). C and D: histogram (number of pixels versus signal intensity) of ROIs from A or C. Histogram in black line with two peaks was obtained from ROIs from Sar and Gr and histogram in red line with one peak was obtained from BFl. Dotted lines showed threshold calculated from maximum entropy method to divide contractile and non-contractile contents. Scale=5 cm

Figure 3

Contractile CSA (A) and non-contractile content (B) in QF, HM, AD and Total thigh muscles for DMD group and CONT group. *, p < 0.05, †, p < 0.01; #, p < 0.001 QF, quadriceps femoris; HM, hamstrings; AD, hip adductors; Total, total thigh muscles measured

Figure 4

Non-contractile content comparison among categorized age groups in DMD. BFl, biceps femoris-long head; RF, rectus femoris; AM, adductor magnus; Gr, gracilis. *, p < 0.02 versus <8 years age group. a, p < 0.02 versus BFl. <8 years age group included boys with DMD under-8-years-old (n = 8); 8 to <10 years age group included boys with DMD older than 8 years but younger than and 10 years (n = 7); 10 to <12 years age group included boys with DMD older than 10 years but younger than 12 years (n = 9); ≥12 age group included boys with DMD 12 years older (n = 4).

Figure 5

Relationship between functional test and non-contractile content (%) in boys with DMD. Note that in Figs. B & C non-ambulatory boys are displayed as triangles, and these subjects were assigned a functional scale 2SD higher than the lowest performance (longest time) on each of the tasks. The assigned values in the non-ambulatory subjects were not included in the correlations analyses and are displayed for visual purpose only. HM, hamstrings.

Figure 6

Relationships between peak torque during isometric knee extension and contractile cross-sectional area (CSA) of the quadriceps femoris (A) and between specific torque and age (B).