Botox Injections in Non-Cranial Nerve VII Innervated Muscles for Facial Synkinesis

Facial synkinesis is a debilitating condition that occurs following injury to the facial nerve (CN7). It results from misdirected nerve regrowth, leading to involuntary, often conflicting muscle movements (e.g., eye closure during smiling or neck muscle tightening). This causes functional impairments (e.g., cheek biting, eating difficulties, reduced visibility), cosmetic concerns, and increased rates of anxiety and depression. Facial synkinesis has been reported in the literature to affect up to 75% of patients with facial nerve injury. Chemodenervation of facial muscle groups using targeted BT injections has become a mainstay treatment for facial synkinesis. Typically, BT is selectively injected into hyperfunctioning CN7-innervated muscles on the injured side to allow for relaxation and restoration of organized muscle contraction. BT may also be injected into CN7-innervated muscles on the contralateral non-affected side, to improve facial symmetry. These injections have been shown across numerous studies to be safe, improve facial symmetry, and decrease severity of synkinesis symptoms. Injections are typically preformed every 3-6 months, depending on the needs of the patient and duration of injection benefit. While synkinesis is thought to predominantly affect CN7 innervated muscles, in our clinical experience many patients also experience painful contracture of non-CN7 innervated muscles, such as the temporalis or master muscles. We therefore routinely inject these muscle groups with BT during patients synkinesis treatments. While patients anecdotally report that injection of non-CN7 innervated muscles improve their synkinesis symptoms in our clinical practice, this has not been systematically studied in the literature. This study therefore aims to investigate whether extending BT injections to non-cranial nerve 7-innervated muscles, specifically the masseter and temporalis muscle, can enhance outcomes for facial synkinesis. Since participants are already receiving BT as standard care, the study introduces no additional risks, focusing only on adjusting injection targets within their existing treatment. This research addresses a critical gap in managing synkinesis, where current treatments are limited, and could lead to refined protocols that enhance patient quality of life by reducing symptoms and improving facial symmetry. The potential benefits-improved function, aesthetics, and mental well-being-outweigh the minimal risks, as the intervention aligns with established, safe practices.