Treatment Response to Botulinum Neurotoxin-A in Children With Cerebral Palsy Categorized by the Type of Stretch Reflex Muscle Activation

Abstract

While Botulinum NeuroToxin-A (BoNT-A) injections are frequently used to reduce the effects of hyperactive stretch reflexes in children with cerebral palsy (CP), the effects of this treatment vary strongly. Previous research, combining electromyography (EMG) with motion analysis, defined different patterns of stretch reflex muscle activation in muscles, those that reacted more to a change in velocity (velocity dependent-VD), and those that reacted more to a change in length (length dependent-LD). The aim of this study was to investigate the relation between the types of stretch reflex muscle activation in the semitendinosus with post-BoNT-A outcome as assessed passively and with 3D gait analysis in children with spastic CP. Eighteen children with spastic CP (10 bilaterally involved) between the ages of 12 and 18 years were assessed before and on average, 8 weeks post-treatment. EMG and motion analysis were used to assess the degree and type of muscle activation dependency in the semitendinosus during passive knee extensions performed at different joint angular velocities. Three-dimensional gait analysis was used to assess knee gait kinematics as a measure of functional outcome. Pre-treatment, 9 muscles were classified as VD and 9 as LD, but no differences between the groups were evident in the baseline knee gait kinematics. Post-treatment, stretch reflex muscle activation decreased significantly in both groups but the reduction was more pronounced in those muscles classified pre-treatment as VD (−72% vs. −50%, p = 0.005). In the VD group, these changes were accompanied by greater knee extension at initial contact and during the swing phase of gait. In the LD group, there was significantly increased post-treatment knee hyperextension in late stance. Although results vary between patients, the reduction of stretch reflex muscle activation in the semitendinosus generally translated to an improved functional outcome, as assessed with 3D gait analysis. However, results were less positive for those muscles with pre-treatment length-dependent type of stretch reflex muscle activation. The study demonstrates the relevance of categorizing the type of stretch reflex muscle activation as a possible predictor of treatment response.

The Short-Term Impact of Botulinum Neurotoxin-A on Muscle Morphology and Gait in Children with Spastic Cerebral Palsy

“…This resulted in a (tendency) towards a reduced difference in EMG between high and low stretch velocity (which exceeded the SEM). These results confirmed previous findings that BoNT-A injections in the MG and ST successfully reduces the hyperactive stretch reflex [ 62 , 64 , 65 ].…”

“…Thereby, more research on dosage dependent effects, the frequency of BoNT-A injections and treatment history is relevant. In order to gain more insights into the patient- and or even muscle-specific response to BoNT-A and in order to properly identify responders and non-responders, the objective measures of muscle spasticity as well as morphology and function, such as gait [ 37 , 39 , 64 , 68 ], should be combined in future studies and implemented in clinical practice. These findings may improve efficient treatment planning.…”

“…A subset of participants (n = 14) underwent an instrumented spasticity assessment in order to objectively evaluate the change in the hyperactive stretch reflex during passive stretch [ 77 ]. This method has been previously described by Bar-On and colleagues [ 77 ] and is proven sensitive enough to detect treatment-induced changes [ 62 , 64 , 65 ].…”

Muscle Characteristics in Pediatric Hereditary Spastic Paraplegia vs. Bilateral Spastic Cerebral Palsy: An Exploratory Study

“…Despite limited data on the effectiveness of BTX injections on focal spasticity and function in children with HSP (6, 7), the presence of high-velocity-dependent phenotypes indicates the potential positive outcomes of BTX treatment. Indeed, in children with SCP, previous research on the effect of BTX demonstrated more pronounced decreases in muscle tone in children with high-velocity-dependent muscle activation patterns compared with length-dependent muscle activation patterns (21). Apart from daily orthotic management and regular physiotherapy as the general treatment approach, the use of BTX is widely applied as tone-reducing treatment in children with bilateral SCP (51).…”

“…Moreover, using such instrumentation, different muscle activation patterns in reaction to increased stretch velocity have been reported (20). Treatment response may differ between these phenotypes, highlighting the importance to use instrumented impairment assessment for treatment guidance (21,22).…”