Effects of Duchenne muscular dystrophy on muscle stiffness and response to electrically-induced muscle contraction: A 12-month follow-up

- DMD patients exhibit a progressive impairment of muscle force transmission.
- Electromechanical delay is sensitive to quantify degenerative effects of DMD.
- Increase in muscle stiffness indicates tissue changes over 12 months in DMD.
- Electromechanical delay and elastography may help detect muscle impairments for research purposes.

The present study aimed to assess the ability of muscle stiffness (shear modulus) and response to electrically-induced muscle contraction to detect changes in muscle properties over a 12-month period in children with Duchenne muscular dystrophy (DMD). Ten children with DMD and nine age-matched healthy male controls participated in two experimental sessions (T0 and T+12months) separated by 12.4 ± 0.9 months. Two contractions of the biceps brachii were electrically-induced during which an ultrasound probe was placed over the muscle. The resting shear modulus was measured using elastography from six muscles. Evoked maximal torque was increased at T+12months in controls (+11.2 ± 7.6%, P <0.001) but was not modified in children with DMD (P = 0.222). Electromechanical delay (+12.9 ± 11.3%, P <0.001) and its force transmission component (+10.1 ± 21.6%, P = 0.003) were significantly longer at T+12months than T0 for children with DMD. The results revealed an increase in muscle stiffness at T+12months in children with DMD for tibialis anterior (+75.1 ± 93.5%, P = 0.043), gastrocnemius medialis (+144.8 ± 180.6%, P = 0.050) and triceps brachii (+35.5 ± 32.2%, P = 0.005). This 12-month follow-up study demonstrates that electromechanical delay and elastography may help detect subtle muscle impairments in patients with DMD. These sensitive outcomes may improve the follow-up of innovative therapeutic interventions within the field of DMD.