Contralateral Upper Limb Weakness Following Botulinum Toxin A Injection for Poststroke Spasticity

Area of Science:

• Neurology
• Pharmacology
• Rehabilitation Medicine

Background:

• Botulinum toxin type A is approved for managing post-stroke spasticity.
• Adverse effects typically involve local reactions or systemic spread.
• Contralateral weakness is a rare complication of botulinum toxin A treatment.

Observation:

• A patient receiving incobotulinum toxin A for right-sided spasticity switched to abobotulinum toxin A (1:3.83 ratio).
• Two weeks post-injection, the patient developed contralateral upper limb paresis, particularly affecting the deltoid muscle.
• Electroneuromyography confirmed a neuromuscular block attributed to botulinum toxin A.

Findings:

• The patient experienced a rare adverse effect of contralateral paresis after switching botulinum toxin A formulations.
• Complete recovery from the paresis occurred over eight months.
• This case highlights the potential for distant side effects following formulation changes.

Implications:

• Switching between different botulinum toxin A formulations requires caution with unit conversions.
• Physicians should be aware of the possibility of rare distant side effects, including contralateral limb weakness.
• Monitoring patients for unexpected neurological deficits after treatment modification is essential.