Role of targeted neuromodulation in the treatment of congenital unilateral lower lip palsy: A clinical case report

Congenital unilateral lower lip palsy (CULLP), or congenital hypoplasia of the depressor anguli oris muscle, also known as asymmetric crying facies, is a rare condition that results in asymmetry of the lower lip during smiling, laughing, and crying. Although the etiology is unknown, weakness of the depressor labii inferioris (DLI) muscle is implicated as a contributing factor. Currently, no well-established treatment options are available. This case report describes an 18-year-old male patient diagnosed with CULLP. Physical examination revealed a symmetric face at rest, but asymmetry when smiling and opening the mouth. Following the administration of lidocaine into the affected DLI muscle, the patient’s smile and lower lip symmetry were immediately restored without any adverse effects. Subsequently, administration of botulinum toxin for neuromodulation of the DLI muscle led to a significant improvement in symmetry and oral function within 2 weeks, which was sustained at 1 month and 3 months post-treatment. No adverse effects were reported, and both patients and families expressed high satisfaction with the outcomes. This case highlights the potential use of neuromodulation as a minimally invasive and effective treatment for CULLP.