Non-invasive assessment of muscle spasticity in children with cerebral palsy undergoing botulinum toxin treatment using near-infrared spectroscopy

Spasticity is a common and debilitating feature of cerebral palsy (CP), often treated with botulinum toxin A (BoNT-A). Standard assessments, such as the Modified Ashworth Scale (MAS), are subjective and prone to inter-rater variability. Near-infrared spectroscopy (NIRS) is a non-invasive method that measures muscle oxygenation and hemodynamics. In CP, spastic muscles exhibit impaired perfusion and abnormal oxygen consumption due to sustained contraction and elevated intramuscular pressure. Prior studies suggest that reducing spastic overactivity improves local tissue oxygenation, indicating that NIRS-derived metrics could objectively reflect spasticity severity and treatment response. To evaluate the feasibility of using NIRS as a biomarker for spasticity severity and treatment response in children with CP receiving BoNT-A and to assess the correlation between NIRS-derived tissue oxygenation index (TOI%) and MAS scores over time. In this prospective pilot study, eight children (aged 2–17 years) with CP undergoing BoNT-A treatment were assessed. Muscle oxygenation was recorded using a portable NIRS device at baseline, 2–4 weeks, 6–10 weeks, 3 months, and 6 months post-injection. Spasticity was measured concurrently using MAS. Temporal changes in TOI% and MAS were analyzed using repeated-measures ANOVA, and associations between the two were evaluated with Pearson correlation. TOI% increased significantly after injection, peaking at 6–10 weeks and 3 months (p < 0.001), then declined toward baseline by 6 months. MAS scores showed a similar trend, with reduced spasticity during peak effect. A moderate, significant negative correlation between TOI% and MAS (r = − 0.409, p < 0.05) indicated higher oxygenation was associated with lower spasticity. NIRS is a feasible, non-invasive tool for assessing muscle spasticity and monitoring BoNT-A response in children with CP. Its correlation with MAS supports physiological relevance and suggests NIRS may offer a more objective measure of spasticity. Larger studies are warranted to validate these findings and support clinical use.