Botulinum toxin A modifies nociceptive withdrawal reflex in subacute stroke patients

Objectives: The aims of this study were to evaluate the pattern of the nociceptive withdrawal reflex (NWR) of the upper limb at rest and after injection of Botulinum toxin type A (BoNT-A) in poststroke subacute hemiparetic patients. Methods: Fourteen patients with poststroke subacute hemiparesis underwent clinical and instrumental evaluation and BoNT-A injection. Painful electrical stimulation was applied to induce the NWR. Baseline EMG activity and NWR recordings (EMG and kinematic response) were performed at T0, one month (T1), and three months (T2) after the BoNT-A injection, as were Modified Ashworth Scale (MAS) and Functional Independence Measure (FIM) scores. Results: Comparison of results at T0, T1, and T2 revealed significant changes in the MAS score for the elbow (p < 0.001) and wrist joints (p < 0.001) and in the FIM score at T0 and T2. BoNT-A injection had a significant effect on both NWR amplitude and baseline EMG activity in the posterior deltoid (PD) and flexor carpi radialis (FCR) muscles as well as in all averaged muscles. Analysis of elbow kinematics before and after treatment revealed that the reflex probability rates were significantly higher at T1 and T2 than at T0. Conclusion: Injection of BoNT-A in the subacute phase of stroke can modify both the baseline EMG activity and the NWR-related EMG responses in the upper limb muscles irrespective of the site of injection; furthermore, the reflex-mediated defensive mechanical responses, that is, shoulder extension and abduction and elbow flexion, increased after treatment. BoNT-A injection may be a useful treatment in poststroke spasticity with a potential indirect effect on spinal neurons.