The effect of botulinum toxin-A on neural and non-neural components of wrist hyper-resistance in adults with stroke or cerebral palsy

Background Botulinum toxin-A (BoNT) is widely used to manage focal upper limb spasticity and is effective in reducing resistance to passive movement, as measured with the modified Ashworth scale. Discrimination and quantification of the underlying neural and non-neural components of hyper-resistance may further improve understanding of the effect of BoNT. Objective To explore the effects of BoNT on neural (NC), non-neural elastic (EC), and viscous (VC) components of resistance to passive wrist extension in adults with stroke or cerebral palsy and the association between the effects on wrist hyper-resistance components and clinical spasticity, pain and motor function scales. Design Pre-experimental study with pre- and post-intervention measurements at 6 and 12 weeks. Setting An outpatient clinic of a hospital. Participants Adults with chronic stroke or cerebral palsy indicated for BoNT treatment for hyper-resistance in the wrist (N = 18). Interventions BoNT injections in the wrist and/or finger flexor muscles. Main Outcome Measures Wrist hyper-resistance components, using the NeuroFlexor, and clinical scales (modified Ashworth scale, Tardieu scale, passive wrist extension, pain, Fugl-Meyer motor assessment of the upper extremity, and action research arm test). Results NC was significantly reduced 6 and 12 weeks post-intervention (median -11.96 Newton, P < .001 and median -9.34 Newton, P = .001, respectively); non-neural EC and VC showed no change. NC reduction 6 weeks post-intervention correlated significantly with BoNT dose (Pearson correlation coefficient r(p) = -0.56). No significant correlations were found between change scores in wrist hyper-resistance components and clinical scales. Conclusions BoNT affected the neural component of resistance to passive wrist extension, while leaving the non-neural elastic and viscous components unaffected. This instrumented approach to quantify the effects of BoNT in the wrist and finger flexor muscles on the components of wrist hyper-resistance may have an added value for BoNT treatment evaluation in clinical practice.