Use of Shearwave Elastography To Quantify Change In Upper Extremity Spasticity Following Botulinum Toxin Injection
Aviva Wolff, EdD, OTR, CHT1; Kristi Wood, MD1; Aaron Daluiski, MD2; Ogonna K. Nwawka, MD1
1Hospital for Special Surgery, New York, NY, 2Hand and Upper Extremity Surgery, Hospital for Special Surgery, New York, NY
Background: Botulinum toxin (BTX) is frequently used to reduce upper extremity (UE) muscle spasticity in individuals with cerebral palsy (CP) to delay or prevent surgery and improve function. Despite frequent use, individual muscle response varies widely. Shearwave elastography (SWE), a quantitative imaging technique, can be used to quantify tissue elasticity. We hypothesized that SWE would detect change in muscle stiffness pre and post BTX injection in upper extremity muscles.
This was a retrospective cohort study. SWE data was retrieved from the medical charts of 7 subjects with spastic CP (6 male, 1 female) between the ages of 9-28 (mean age=16±6) who received BTX injections. Data was excluded if subjects had an unrelated orthopedic injury to the affected UE, were undergoing concurrent oral or intrathecal anti-spasticity therapy, or had prior BTX injection in preceding 6 months.
SWE data was extracted and analyzed. A total of 19 spastic muscles underwent ultrasound guided intra-muscular BTX per dosing guidelines. Dosing ranged from 36-200 units per muscle. SWE measures were taken before and immediately after BTX injection and included muscle thickness (cm), muscle echogenicity, and muscle elasticity (E) measured in kilopascal (kPa) in longitudinal and transverse muscle orientations. A paired t-test was performed on elasticity measures pre and post BTX injection.
Results: Nineteen muscles were included in the final analysis (4 biceps, 4 brachialis, 3 flexor carpi ulnaris (FCU), 3 flexor carpi radialis (FCR), 2 flexor digitorum superficialis (FDS), 1 flexor digitorum profundus (FDP), 1 flexor pollicis longus (FPL), and 1 pronator teres (PT). Overall, all muscles exhibited a notable change in SWE post BTX. Average decrease in elasticity was 31.7% for biceps, 28.4% for brachialis, 40.0% for FCR, 37.1% for FCU, 58.4% for FDP, 59.1% for FDS, 49.7% for FPL and 71.3% for PT. Significant differences were found for biceps, brachialis and FDS. Although cross-muscle comparison is difficult, overall greater changes were seen in the wrist and finger flexor-pronators (mean decrease of 52.6% +/- 12.9%) than the elbow flexors (30.1% +/- 2.3%).
Conclusion: SWE detected variable levels of changes in muscle stiffness in UE muscles groups post BTX injection. These findings, indicate that SWE can be used to quantify muscle stiffness in the UE and has potential to impact clinical decision making and outcomes. This preliminary data supports future prospective studies of a larger and more robust cohort to study the predictive value of muscle stiffness properties to response to treatment.
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