Treatment for "Asymmetric Crying Facies"

This study focuses on children with hemifacial microsomia (HFM), a common congenital craniofacial deformity caused by abnormal development of the first and second branchial arches. Up to 45% of children with HFM have facial nerve dysplasia, most frequently involving the mandibular marginal branch. These children present with asymmetric lower-lip movement called "crooked-mouth smile" during smiling, speaking or crying. Unlike asymmetric crying syndrome, this condition does not resolve spontaneously and may gradually get worse. "Crooked-mouth smile" results from muscle weakness of the lower lip on the affected side, leading to dynamic perioral muscle imbalance. Static treatment includes botulinum toxin injection, muscle resection, nerve cutting and fascia suspension; dynamic treatment includes muscle transfer procedures. Early intervention is important for children's psychological well-being. Botulinum toxin injection is minimally invasive, safe and reversible, and is regarded as a preferred initial therapy. However, prospective clinical evidence regarding its efficacy, safety and appropriate dosage in this pediatric population remains insufficient. This prospective study aims to explore the safety, effectiveness and optimal dose of botulinum toxin injection for treating "crooked-mouth smile" in children with HFM and mandibular marginal branch dysplasia.