Congenital unilateral lower lip palsy: a case-based review

Congenital unilateral lower lip palsy (CULLP), also referred to as congenital asymmetric crying facies (ACF), is a rare condition that causes pronounced depression of the unaffected lower lip when crying, despite symmetric appearance of the mouth and lips at rest. Unlike the acquired form of ACF, CULLP is idiopathic and often involves permanent defect.

We present a case-based review of CULLP, including a thorough analysis of the relevant literature and a discussion of the exemplary case of 5-year-old patient presenting with unilateral facial asymmetry resulting from left-sided facial weakness. The patient was diagnosed with ACF at birth, and documentation from a previous neurologic consultation specifies the root cause of the asymmetry as developmental aplasia of the left depressor anguli oris muscle (DAOM). However, there is no record of electrodiagnostic testing or B-scan ultrasound imaging that would support this conclusion, and the patient's dysarthric speech may suggest lower motor neuron involvement. Botox chemodenervation of the right, unaffected side was recommended to deanimate the contralateral lower lip and achieve facial symmetry, in addition to potentially resolving some of the patient's speech difficulties.

There are several approaches, both surgical and non-surgical, to the management and correction of CULLP. These include weakening the muscles of the contralateral side or increasing muscular tension on the ipsilateral side, referred to as deanimation and reanimation procedures, respectively.