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Congenital unilateral lower lip palsy is a congenital anomaly that is caused by agenesis or hypoplasia of depressor anguli oris muscle. Unilateral depression of the lower lip is seen during smiling or crying. This activity outlines the evaluation and management of congenital unilateral lower lip palsy and highlights the role of the interprofessional team in managing patients with this condition. Objectives: Describe the etiology of congenital unilateral lower lip palsy. Identify the typical presentation of a patient with congenital unilateral lower lip palsy. Summarize the treatment algorithm of congenital unilateral lower lip palsy. Review the importance of improving care coordination amongst the interprofessional team to enhance the delivery of care for patients with congenital unilateral lower lip palsy. Access free multiple choice questions on this topic.

Congenital unilateral lower lip palsy is a rare congenital anomaly with an estimated incidence of 0.5-1% in newborns or 1 per 160 live births.[1][2] The condition occurs secondary to unilateral agenesis or hypoplasia of the depressor anguli oris muscle. The depressor angularis oris muscle is a triangular muscle that originates from the mandible and extends to the angle of the mouth. It is mainly innervated by two facial nerve branches, the buccal and the mandibular branch. It depresses the lower corner of the mouth and pulls it laterally. Therefore, it facilitates expressing sadness while crying. In cases of hypoplasia/agenesis of the depressor angularis oris muscle, no mouth/lip movement is seen on the hypoplasia side while the corner of the mouth is pulled downwards on the normal side.[3]

The etiology of congenital unilateral lower lip palsy is multifactorial. It can be seen as a result of facial nerve compression or because of a faulty facial nerve or muscle development. Approximately 80% of patients are found to have underlying facial nerve/muscle development defects, and 20% of patients have facial nerve compression.[2] The marginal mandibular branch of the facial nerve is prone to compressive injuries in the antepartum and intrapartum period. For the vast majority of CULLP cases, faulty facial muscle/nerve development is the underlying etiology.[2] Etiologies that affect the proper development of the depressor anguli oris muscle include intrauterine viral infectious and structural brainstem anomalies as well as genetic factors.

In a majority of congenital unilateral lower lip palsy cases (approximately 80%), left-sided asymmetry was seen.[4] It can be seen as an isolated clinical finding. However, it can also be associated with various congenital abnormalities in approximately 45% to 70% of cases.[5] Autosomal dominant inheritance has been reported in some facial cases with variable expressivity.[2]

The typical clinical presentation is the unilateral depression of the lower lip during smiling or crying. Exaggerated lower lip depression is seen on the normal side. There is contralateral lower lip weakness. The face appears symmetric at rest. There is no eyelid closure, forehead movement, and nasolabial fold depth asymmetry.[6] Affected patients do not have any difficulties with swallowing, chewing, or speaking.

Diagnosis is made based on neurological exam findings. Detection of unilateral lower lip palsy warrants a careful examination and thorough evaluation for other congenital abnormalities, especially cardiovascular anomalies.[7] CULLP can be associated with other systemic anomalies such as the central nervous system, head and neck, respiratory, musculoskeletal, and genitourinary system anomalies.[8] Cervicofacial anomalies can occur on the same side as hypoplasia of the depressor anguli oris muscle. DiGeorge, VACTERL syndromes (vertebral abnormalities, anal atresia, heart defects, tracheoesophageal fistula, esophageal atresia, kidney and radius abnormalities, other limb abnormalities) and Cayler cardiofacial syndrome are specific syndromes which are associated with CULLP.[7] In a large retrospective review, 14% of CULLP patients were found to have DiGeorge Syndrome.[9] Therefore, congenital unilateral lower lip palsy can be considered as a clinical marker for possible congenital anomalies.

In isolated cases of congenital unilateral lower lip palsy without any underlying congenital anomalies, the outcome is good and generally, no treatment is required. If cosmetic concerns persist, reconstruction surgery can be considered for facial asymmetry.[10] Chemodenervation of the contralateral muscle with botulinum toxin A is considered a safe and minimally invasive method to improve facial asymmetry in recent case studies.[11][12] A minimally invasive surgical intervention using horizontal and vertical fascia grafting method is also reported to improve facial asymmetry in selected cases.[13] Ultrasound imaging of facial muscles and electrodiagnostic testing can be considered for further management.[2] Normal findings would be expected on electrodiagnostic testing of the facial nerve and other, noninvolved, muscles of facial expression. Given the frequent association with Di George syndrome, further screening for 22q11.2 deletion is recommended in some studies.[9] An interprofessional team approach with long term follow up is necessary in such cases to ensure appropriate management and a good prognosis.[14]

Congenital unilateral lower lip palsy is differentiated from facial nerve palsy on the basis of the neurological exam. Patients with CULLP are expected to have symmetric forehead wrinkling, eye closure, and nasolabial fold depth.[3] Unilateral facial nerve paralysis should be suspected in cases with absent forehead wrinkling, facial asymmetry, incomplete eye closure, drooling, and feeding problems related to lip asymmetry.[15] A comprehensive history and careful clinical examination are essential for an accurate diagnosis. This is important as the treatment regimen is different for facial nerve paralysis and includes prevention of eye exposure, and means to avoid nasal deviation and drooling while working around the lack of labial function.[15]

Prognosis is good in isolated CULLP cases, and treatment may not be required. Clinical improvement is generally observed over time in cases with facial nerve compression. However, the resolution of symptoms may not be seen in the setting of developmental defects, and long term follow up is necessary with an interprofessional team approach.

In isolated cases, no complications have been reported related to lower lip palsy. Affected patients do not have any problems with feeding, eye closure, or breathing. However, in the setting of association of other congenital anomalies, complications may be seen depending on the affected system.

Congenital unilateral lower lip palsy is a minor congenital anomaly that only affects the lower lip movements. When the baby cries, the mouth is pulled downwards on the healthy side and does not move on the affected side. Parents should be counseled that affected children do not have any difficulties with eye movements, feeding, or breathing. It can result from a traumatic injury to the nerve in the antenatal or peripartum period or from a developmental problem of the facial nerve or of the affected muscle. While it can be an isolated finding, in some cases it can be accompanied by other congenital anomalies such as heart defects, musculoskeletal defects (less frequently), kidney problems, neck or face problems, etc. and parents should be encouraged to be compliant with the recommended consultations and evaluations. Whenever there are other underlying anomalies, patients should be followed by an interprofessional team. Parents should also be educated that the outcome is good in isolated cases, and no treatment is required in most cases. If cosmetic concerns persist, minor surgeries or botox injections may provide a good outcome.

A detailed physical examination of newborns is very important for the diagnosis of congenital unilateral lower lip palsy. An interprofessional team approach should be used for the evaluation and management of patients with CULLP. In selected cases, clinicians can use electrodiagnostic testing or ultrasonography to differentiate CULLP from facial nerve paralysis. Clinicians should be aware that some cases of CULLP can be associated with additional various congenital anomalies. A thorough evaluation should be started after the diagnosis. Early and accurate diagnosis provides early detection of other congenital anomalies as well as adequate parental education regarding the prognosis and possible treatment options.