Original Editor - Wendy Walker
Introduction and Definition[edit | edit source]
Synkinesis (AKA aberrant regeneration) occurs after injury to the facial nerve and it is a common sequelae of facial palsy. The cause of the injury may be Bell's Palsy, Ramsay Hunt Syndrome (less common), surgical damage (eg. during surgical removal of an acoustic neuroma), trauma (skull fractures) or other conditions causing facial paralysis.
Synkinesis = "syn" meaning "together" and "kinesis" meaning "movement". Therefore, synkinesis means "moving together" or "mass movement". Thus, synkinesis is when an involuntary movement accompanies a voluntary movement.
The type of synkinesis is commonly described by combining the names of the two involved muscle groups, with the first part referring to the voluntary motor group and the second part referring to the involuntary muscle group. For instance:
- Ocular-oral synkinesis is when voluntary eye contraction such as blinking or brow lifting elicits an involuntary mouth movement
- Oral-ocular synkinesis is when an involuntary eye contraction accompanies a volitional mouth movement such as smiling and lip puckering
Clinically Relevant Anatomy[edit | edit source]
The facial nerve is the seventh cranial nerve, and it controls the muscles of facial expression. More information on the anatomy of the facial nerve is available here.
Mechanism of Injury / Pathological Process[edit | edit source]
The unintentional or mass movements are thought to be caused by an undifferentiated regeneration of the facial nerve that occurs after it has been compressed or damaged.
It is thought that synkinesis could be caused by four possible mechanisms:
- Aberrant regeneration - "miss-wiring"
- Axons regrow from the facial nucleus to incorrect peripheral muscle groups
- It has generally been assumed that the site of the miss-wiring is the lesion site (i.e. where the nerve was damaged by crush / inflammation), but one 2004 study found that the regrowing axons are disorganised along their whole length, as well as at the lesion site
- Ephaptic transmission - electrical cross-talk between nerve branches
- Presumed to be due to the reduced myelin sheath of the nerve fibres, which means they are poorly insulated
- Nuclear hyperexcitability
- This theory proposes that once the post-synaptic cell loses its input from the degenerated axons, it creates additional neurotransmitter receptors and, thus, becomes hypersensitive
- Because of this hypersensitivity, it responds to neurotransmitters provided by another nerve nearby
- Maladaptive cortical plasticity
- A 2018 study using MRI found that there was cortical reorganisation in the primary sensorimotor area and the supplementary motor area in the brain
Many authors think that a combination of more than one, and possibly all, of these mechanisms is likely to be involved.
Clinical Presentation[edit | edit source]
While patients experience recovery and re-innervation of the affected side of the face after flaccid facial palsy, they also experience the involuntary linking of movements which are typical of synkinesis.
The effects which are most commonly observed are:
- When moving the mouth (e.g. smile, lip pucker, when eating), the eye on the affected side moves towards partial (or occasionally full) closure, whereas the unaffected eye remains wide open = oral-ocular
- When raising the eyebrows or closing the eyes, the corner of the mouth on the affected side of the face raises = ocular-oral
It is important to recognise that synkinesis frequently starts to occur from the fifth or sixth month post onset of palsy, although in some instances it can present as early as the third month post onset, and generally increases for up to two years post onset.
Scoring / Measuring Synkinesis[edit | edit source]
The most commonly used measure of facial range of movement by surgeons and physicians is the House-Brackmann scale. Unfortunately, this scale does not have a rating for the aberrant linking of movements which occurs in synkinesis.
The Sunnybrook Facial Grading System [FGS] is a more comprehensive scoring system for facial range of movement, and it has a section dedicated to rating the presence of synkinesis movements. A 2015 systematic review of facial nerve grading systems identified the FGS as meeting the most criteria in regards to overall assessment of facial nerve function, sequelae and response to treatments. It was also identified as having the highest reliability. The FGS is sensitive enough to show gains when facial range of movement increases as well as if the person has a reduction in their synkinesis.
The Synkinesis Assessment Questionnaire consists of nine questions and has been shown to be both valid and reliable as a dedicated measurement of synkinesis. It has also been shown to have good correlation with the synkinesis component of the FGS.
- Pattern I: Good smile (i.e. good range of movement) with mild synkinesis
- Pattern II:Acceptable smile with moderate to severe synkinesis
- Pattern III: Unacceptable smile (little or no range of movement) with severe synkinesis
- Pattern IV: Poor smile with mild synkinesis
This method of scoring synkinesis has not been assessed in inter- and intra-rater reliability studies, but it proved a useful tool to help decide on management in the study by Chuang.
Management / Interventions[edit | edit source]
Physiotherapy Interventions[edit | edit source]
The following physiotherapy interventions have been shown to be effective in reducing or minimising synkinesis:
Non-Physiotherapy Interventions[edit | edit source]
- Botulinum toxin injections
Differential Diagnosis[edit | edit source]
Synkinesis is a clinical diagnosis. It is usually easy to diagnose as the patient will display clear linking of facial movements on the affected side only, and will have a history of facial palsy. Occasionally it can be confused with the following conditions:
- Facial dystonia
- Essential blepharospasm
- Essential hemifacial spasm
Resources[edit | edit source]
References[edit | edit source]
References will automatically be added here, see adding references tutorial.
- Ma ZZ, Lu YC, Wu JJ, Li SS, Ding W, Xu JG. Alteration of spatial patterns at the network-level in facial synkinesis: an independent component and connectome analysis. Ann Transl Med. 2021;9(3):240.
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