No Gait, No Problem: Using Shear Wave Elastography to Identify Affected Muscles in Sport-Induced Dystonia

Background and/or Objectives: Task-specific dystonia is a complex, debilitating condition characterized by muscle overactivity resulting in abnormal posturing during repeated, overused movements. In the lower limbs, it can prove difficult to accurately identify which muscles are principally involved without formal gait analysis. This study evaluated the use of ultrasonic shear wave elastography (SWE) to identify primary dystonic muscles in lower limb, sport-induced dystonia.

Design: Dystonic muscles in affected limb were identified using clinical 3D gait analysis with surface electromyography. After 15 minutes of rest, baseline pre-exercise shear wave data of dystonic and control muscles were obtained. Participants then performed task-specific movements (running (n=1), walking (n=1), lunging (n=1)) to sustain dystonic symptoms for 3 minutes. Post-exercise shear wave data of the same muscles were obtained for comparison. Shear wave data for the same muscle in the uninvolved, contralateral (control) limb of each patient were captured pre- and post-exercise.

Setting : Movement Disorders Clinic and Gait Lab

Participants : Three adult, athlete participants were evaluated by movement disorders and PM&R teams to confirm diagnosis of task-specific lower limb dystonia.

Interventions: N/A

Main Outcome Measures: Qualitative assessment of change in color-coded SWE images pre- and post-exercise.

Results: Post-exercise shear wave images accurately identified increased stiffness in dystonic muscles that correlated to dystonic patterns on gait analysis in all three subjects: Fibularis brevis and longus in eversion “whip” gait, soleus in plantar-flexion gait, and semimembranosus and biceps femoris in excessive knee flexion gait. Post-exercise shear wave images in control muscles did not demonstrate any qualitative changes in stiffness.

Conclusions: This case series demonstrates the utility of SWE in identifying dystonic muscles in lower limb sport-related dystonia with complex gait patterns, especially in the absence of formal gait analysis. Ultrasonic SWE may be a potential diagnostic tool to guide and expedite early, targeted therapeutic interventions, leading to improved outcomes and quality of life for these patients.