Post-Paralytic Facial Synkinesis
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Disease Entity
Disease
Post-paralytic facial synkinesis is an acquired disorder of facial movement characterized by involuntary contraction of one or more facial muscles during voluntary activation of other facial muscles. It develops following injury to the facial nerve (cranial nerve VII) and subsequent maladaptive changes in facial nerve signaling and motor control, resulting in abnormal coordination of facial movements. The condition most commonly occurs following peripheral facial nerve palsy, including Bell's palsy, and may lead to functional impairment, facial asymmetry, and reduced quality of life. [1]
Facial synkinesis may involve various combinations of facial muscles. The nomenclature is based on the direction of synkinetic movement, with the first term indicating the intended voluntary movement and the second term describing the associated involuntary movement. Two clinically important patterns involving the periocular and perioral musculature include:
- Oral-ocular synkinesis: Involuntary contraction of the orbicularis oculi muscle during voluntary oral movements, such as smiling, speaking, chewing, or opening the mouth, resulting in narrowing or closure of the palpebral fissure. Marin-Amat syndrome is a specific manifestation of oral-ocular synkinesis characterized by involuntary eyelid closure during jaw movement, particularly jaw opening, typically following peripheral facial nerve palsy.
- Ocular-oral synkinesis: Involuntary contraction of the perioral or midfacial muscles during voluntary eye closure or blinking, resulting in abnormal movements of the mouth or cheek.
Both patterns may coexist in the same patient and vary in severity, potentially resulting in functional impairment and facial asymmetry. [1][2]
Etiology
Post-paralytic facial synkinesis develops following injury to the facial nerve (cranial nerve VII) with subsequent recovery of motor function. The most common preceding condition is Bell's palsy, although synkinesis may develop following facial nerve injury from various other causes, including trauma, infection, neoplasms, and surgical interventions. [1][3][4]
Infectious causes include Ramsay Hunt syndrome (herpes zoster oticus), Lyme disease, and other infections affecting the facial nerve. Traumatic and iatrogenic injuries may result from temporal bone fractures, penetrating facial trauma, or surgical procedures involving the facial nerve, particularly parotid and skull base surgery. Neoplastic causes include tumors involving or compressing the facial nerve, such as facial nerve schwannomas, vestibular schwannomas, and parotid malignancies.[3][4]
The development of synkinesis is influenced by the severity of facial nerve injury and subsequent regeneration. According to the Sunderland classifications, neurapraxia (Sunderland grade I) involves temporary conduction block without axonal damage and typically resolves without synkinesis. In contrast, axonal injuries (Sunderland grades II–V) may result in aberrant reinnervation and synkinesis, depending on the extent of nerve damage and subsequent recovery. [5][6]
Pathophysiology
The pathophysiology of post-paralytic facial synkinesis is multifactorial, involving peripheral nerve regeneration and changes in central motor control following facial nerve injury. Aberrant axonal regeneration is the most widely accepted mechanism, although several additional mechanisms have been proposed. [1][3]
- Aberrant axonal regeneration: Following facial nerve injury, regenerating motor axons may be misdirected toward unintended muscle groups. Collateral sprouting may allow a single motor neuron to innervate multiple facial muscles, resulting in involuntary contraction of one muscle during voluntary activation of another. This mechanism is supported by electrophysiological studies demonstrating abnormal coactivation of facial muscles.
- Ephaptic transmission: Incompletely remyelinated or damaged facial nerve axons may permit abnormal electrical transmission between adjacent nerve fibers, resulting in unintended muscle activation. Although this mechanism has been proposed as a contributor to facial synkinesis, direct evidence in affected patients remains limited.
- Facial motor nucleus hyperexcitability: Facial nerve injury may produce changes in the excitability of motor neurons within the facial nucleus in the brainstem. Altered excitatory and inhibitory inputs may lead to abnormal activation of multiple facial muscle groups during voluntary movement.
- Cortical reorganization: Facial nerve injury and subsequent recovery may induce maladaptive neuroplastic changes in cortical regions responsible for facial motor control. Functional neuroimaging studies have demonstrated altered cortical activation and connectivity in patients with facial synkinesis, potentially contributing to abnormal coordination of facial movements. [7]
These mechanisms may act together to produce the characteristic involuntary facial movements observed in oral-ocular and ocular-oral synkinesis.
Diagnosis
History
Patients with post-paralytic facial synkinesis typically report a history of peripheral facial nerve palsy followed by partial or complete recovery of voluntary facial movement. Synkinesis generally becomes apparent several months after the initial injury as facial nerve function returns.[1][3]
Patients may describe involuntary facial movements triggered by specific voluntary actions. In oral-ocular synkinesis, smiling, speaking, chewing, or opening the mouth may produce involuntary eyelid narrowing or closure. Conversely, patients with ocular-oral synkinesis may experience involuntary movement of the mouth or cheek during blinking or voluntary eye closure. Associated symptoms may include facial tightness, muscle spasms, asymmetry, and functional or cosmetic concerns.[8]
Physical Examination
Physical examination should assess facial symmetry, resting muscle tone, voluntary facial movements, and involuntary muscle contractions. Patients should be observed at rest and during specific facial movements to identify patterns of synkinesis.[1]
To evaluate oral-ocular synkinesis, patients are instructed to smile, pucker their lips, open their mouth, and move their jaw laterally while the examiner observes for involuntary narrowing or closure of the palpebral fissure. Conversely, ocular-oral synkinesis is assessed by asking patients to blink and gently or forcefully close their eyes while observing for involuntary movement of the mouth, cheek, or chin.[9]
Additional findings may include facial asymmetry, muscle hypertonicity, tightness, and intermittent facial spasms. Examination should also assess eyelid closure, lagophthalmos, blink function, and ocular surface exposure, particularly in patients with residual facial nerve weakness.
Clinical Diagnosis
Post-paralytic facial synkinesis is primarily a clinical diagnosis based on a history of facial nerve injury and the presence of involuntary facial muscle contractions during voluntary movements. Additional testing is generally not required when the history and examination are characteristic.
Standardized assessment tools, including the Sunnybrook Facial Grading System, eFACE, and Synkinesis Assessment Questionnaire (SAQ), may be used to evaluate synkinesis severity and monitor treatment response.[10][11][12]
Electromyography (EMG) may be used to identify abnormal coactivation of facial muscles, characterize synkinetic patterns, and assist with treatment planning. Magnetic resonance imaging (MRI) is not routinely indicated for typical post-paralytic synkinesis but may be warranted in patients with atypical presentations, unclear history of facial nerve injury, progressive facial weakness, or suspected structural lesions affecting the facial nerve.
Differential Diagnosis
- Hemifacial spasm
- Benign essential blepharospasm
- Inverse Marcus Gunn phenomenon
- Marcus Gunn jaw-winking syndrome
- Eyelid myokymia
- Ocular myasthenia gravis
- Aponeurotic ptosis
Management
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General Treatment
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Medical Therapy
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Surgery
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Complications
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Prognosis
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Additional Resources
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References
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- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Guntinas-Lichius O, Prengel J, Cohen O, et al. Pathogenesis, diagnosis and therapy of facial synkinesis: A systematic review and clinical practice recommendations by the international head and neck scientific group. Front Neurol. 2022;13:1019554. doi:10.3389/fneur.2022.1019554.
- ↑ Oyer SL, et al. International, Multispecialty Expert Consensus on Nomenclature for Facial Paralysis. Facial Plast Surg Aesthet Med. 2025. doi:10.1177/26893614251363957.
- ↑ 3.0 3.1 3.2 3.3 Rail B, Henn D, Wen YE, Tavares-Ferreira D, Rozen SM. Clinical Perspectives on the Pathophysiology of Facial Synkinesis: A Narrative Review. JAMA Otolaryngol Head Neck Surg. 2025;151(3):268–275. doi:10.1001/jamaoto.2024.4489.
- ↑ 4.0 4.1 Hohman MH, Hadlock TA. Etiology, diagnosis, and management of facial palsy: 2000 patients at a facial nerve center. Laryngoscope. 2014;124(7)–E293.
- ↑ Sunderland S. A classification of peripheral nerve injuries producing loss of function. Brain. 1951;74(4):491–516.
- ↑ Scharpf J, et al. Critical Review and Consensus Statement for Neural Monitoring in Otolaryngologic Head, Neck, and Endocrine Surgery. Otolaryngol Head Neck Surg. 2022;166(2):233–262.
- ↑ Singerman K, Kaczorowski-Worthley A, Ramesh U, Lepping RJ, Flynn J. Beyond the nerve: Understanding cortical contributions to post-paralytic facial synkinesis. Behav Brain Res. 2026;510:116254. doi:10.1016/j.bbr.2026.116254.
- ↑ Jethani J. Marin-Amat syndrome: A rare facial synkinesis. Indian J Ophthalmol. 2007;55(5):402–403. doi:10.4103/0301-4738.33832.
- ↑ Shokri T, Patel S, Ziai K, Harounian J, Lighthall JG. Facial synkinesis: A distressing sequela of facial palsy. Ear Nose Throat J. 2024;103(6)–NP391. doi:10.1177/01455613211054627.
- ↑ Ross BG, Fradet G, Nedzelski JM. Development of a sensitive clinical facial grading system. Otolaryngol Head Neck Surg. 1996;114(3):380–386. doi:10.1016/S0194-5998(96)70206-1.
- ↑ Banks CA, Bhama PK, Park J, Hadlock CR, Hadlock TA. Clinician-graded electronic facial paralysis assessment: The eFACE. Plast Reconstr Surg. 2015;136(2):223e–230e.
- ↑ Mehta RP, WernickRobinson M, Hadlock TA. Validation of the Synkinesis Assessment Questionnaire. Laryngoscope. 2007;117(5):923–926. doi:10.1097/MLG.0b013e3180412460.
