Assessing the immediate impact of botulinum toxin injection on impedance of spastic muscle

- The manuscript aims to investigate the immediate impact of Botulinum Toxin A (BoNT-A) injection on the inherent electrical properties of spastic muscle using the newly developed electrical impedance myography (EIM) technique.
- Muscle impedance and anisotropy features were examined in spastic muscles before and after BoNT-A injection.
- There is a significant change of muscle resistance in the injected muscle which could be related to the injection of BoNT-A-saline solution indicating high sensitivity of the EIM technique in detection of muscle composition alterations.

This study aimed to investigate the immediate impacts of Botulinum Toxin A (BoNT-A) injections on the inherent electrical properties of spastic muscles using a newly developed electrical impedance myography (EIM) technique. Impedance measures were performed before and after a BoNT-A injection in biceps brachii muscles of 14 subjects with spasticity. Three major impedance variables, resistance (R), reactance (X) and phase angle (θ) were obtained from three different configurations, and were evaluated using the conventional EIM frequency at 50 kHz as well as multiple frequency analysis. Statistical analysis demonstrated a significant decrease of resistance in the injected muscles (Multiple-frequency: Rpre = 25.17 ± 1.94 Ohm, Rpost = 23.65 ± 1.63 Ohm, p < 0.05; 50 kHz: Rpre = 29.06 ± 2.16 Ohm, Rpost = 27.7 ± 1.89 Ohm, p < 0.05). Despite this decrease, there were no substantial changes in the reactance, phase angle, or anisotropy features after a BoNT-A injection. The significant changes of muscle resistance were most likely associated with the liquid injection of the BoNT-A-saline solution rather than the immediate toxin effects on the muscle. This study demonstrated high sensitivity of the EIM technique in the detection of alterations to muscle composition.