Congenital unilateral lower lip palsy: a case-based review

Abstract

Background
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.Methods and resultsWe 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.Conclusions
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.

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Child's Nervous System (2023) 39:35–40
https://doi.org/10.1007/s00381-022-05695-1
CASE-BASED REVIEW
Congenital unilateral lower lip palsy: acase‑based review
BrandonR.Block1,2 · DeborahStraka‑DeMarco1· MicheleDemarest3· CatherineA.Mazzola1
Received: 29 July 2022 / Accepted: 27 September 2022 / Published online: 6 October 2022
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2022
Abstract
Background 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.
Methods and results 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). How-
ever, 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, unaf-
fected 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.
Conclusions 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.
Keywords Asymmetric crying facies· Depressor anguli oris muscle· Marginal mandibular branch· Dysarthria
Introduction
Asymmetric crying facies (ACF) is a form of unilateral
facial asymmetry, with a symmetric appearance of the
mouth and lips at rest but pronounced depression of the
unaffected lower lip when crying [1]. Some affected indi-
viduals present with slight thinning of the lip on the ipsi-
lateral, non-depressed side [1]. ACF can be either acquired
or congenital, with differential diagnosis achieved through
electrodiagnostic testing or B-scan ultrasound imaging of
the facial muscles [1]. Whereas acquired ACF is expected
to resolve spontaneously within 10months, the congenital
form, also referred to as congenital unilateral lower lip palsy
(CULLP), is a permanent defect, involving incomplete or
absent development of the depressor muscles responsible for
the downward movement of the lower lip and/or the marginal
mandibular branch (MMB) of the facial nerve [2].
Historical background
ACF is generally identified during the initial physical assess-
ment of the newborn, with an incidence of approximately 1
in every 160 live births [2]. The side of the face where the
defect is present does not appear to correlate with sex, but the
left lower lip is affected in approximately 80% of cases [3].
There are four sets of facial muscles that are primarily
responsible for the downward movement of the lower lip
when crying: the depressor anguli oris muscle (DAOM),
the depressor labii inferioris muscle (DLIM), the mentalis
muscle, and the platysma muscle [1]. The former three mus-
cles are all innervated by the marginal mandibular branch
(MMB) of the facial nerve, also known as cranial nerve VII,
which is responsible for innervating the entire facial mus-
culature [4].
* Brandon R. Block
brandon.block@icahn.mssm.edu
1 New Jersey Pediatric Neuroscience Institute, 131 Madison
Ave 3rd Floor, Morristown, NJ07960, USA
2 Icahn School ofMedicine atMount Sinai, NewYork, NY,
USA
3 Morris Speech Therapy, Morristown, NJ, USA
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