Facial Nerve Palsy after Botulinum Toxin Therapy for Hemifacial Spasm: A Case Report

We herein report a case of left hemifacial spasm (HFS) developed ipsilateral facial nerve palsy 5 days after botulinum toxin type A (BTX-A) injection. Multiple facial muscles presented weakness regardless of BTX-A injection and electrophysiological study revealed left facial nerve palsy. Facial nerve palsy improved completely after 24 weeks. Facial nerve palsy is a common disease and could occur as a coincidence. On the other hand, BTX-A might cause neuropathy in some previously reported cases and our case. Although the pathogenesis of neuropathy following BTX-A injection has not been elucidated, this is the first case of ipsilateral facial nerve palsy following BTXA injection for HFS. Thorough neurological examination and electrophysiological study were useful for distinguishing facial nerve palsy from facial muscles weakness related with botulinum toxin.