Contralateral Weakness Following Botulinum Toxin for Post-Stroke Spasticity (P04.091)

Abstract

Objective: We present two patients receiving Botulinum Toxin-A for post-stroke spasticity who developed isolated contralateral limb weakness. Background Botulinum toxin (BoNT) is considered safe and effective in the treatment of post-stroke spasticity. Randomized controlled trials have shown that BoNT is effective in reducing muscle tone and improving disability in the areas of pain, personal hygiene, dressing, and limb position. Adverse effects have generally been mild, including weakness of injected and neighboring muscles. These two cases illustrate an unusual adverse effect of BoNT with its pathophysiology supported by electrodiagnostic testing. Design/Methods: Two patients received high doses of botulinum toxin-Type A (OnabotulinumtoxinA) with large dilution volumes and injection of proximal upper extremity muscles. Both patients developed isolated weakness of the contralateral limb. Following this adverse event both patients underwent electrodiagnostic testing of the affected limb, including repetitive nerve stimulation and EMG. Results: Repetitive nerve stimulation testing of motor nerves in the limb contralateral to the injections demonstrated a decrement of 23% and 16%, respectively. EMG revealed spontaneous activity and small polyphasic units with reduced recruitment in affected muscles. These findings are consistent with severe blockade of the neuromuscular junction. Both patients subsequently improved. Conclusions: This adverse effect of botulinum toxin, with weakness involving only the contralateral upper extremity, suggests diffusion of toxin through tissue planes from proximal upper extremity muscles, across the midline, to contralateral muscles. High doses of botulinum toxin, high volume dilutions, and injection of proximal upper extremity muscles appear to be risk factors for this important adverse effect. Disclosure: Dr. Thomas has nothing to disclose. Dr. Simpson has received personal compensation for activities with NeurogesX, Eli Lilly, Astra Zeneca, Newron, Allergan, Pfizer, Endo, Covidien, Astellas, Ipsen, Gilead, Merz and GlaxoSmithKline. Dr. Simpson has received research support from NeurogesX, Pfizer, Eli Lilly, and Allergan.