Synkinesis

Original Editor - Wendy Walker

Lead Editors  

Introduction & Definition

Synkinesis (AKA aberrant regeneration) occurs after injury to the facial nerve, as a common sequelae of facial palsy.

The cause of the injury may be simple Bell's Palsy, the less common condition Ramsey Hunt Syndrome, surgical damage (eg. during surgical removal of Acoustic Neuroma) or trauma (skull fractures).

Synkinesis = "syn" meaning "together and "kinesis" meaning movement. Therefore synkinesis means "moving together" or "mass movement".

Synkinesis is an involuntary movement accompanying a voluntary one. These unintentional movements are thought to be caused by an undifferentiated regeneration of the facial nerve that occurs after being compressed or damaged.

Clinically Relevant Anatomy

The facial nerve is the 7th cranial nerve, and it controls the muscles of facial expression.

Refer to the Facial Nerve page for more details of its anatomy. 

Mechanism of Injury / Pathological Process

The unintentional or mass movements are thought to be caused by an undifferentiated regeneration of the facial nerve that occurs after being compressed or damaged.

There are 3 possible mechanisms which it is thought could be the cause of synkinesis:

1. Aberrant regeneration
2. Ephaptic transmission
3. Nuclear hyperexcitability

It is possible that a combination of 2 or all 3 of these mechanisms is involved.

Clinical Presentation

Following flaccid facial palsy, as the patient experiences recovery and reinnervation of the affected side of the face, 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 (eg. 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
• when raising the eyebrows or closing the eyes, the corner of the mouth on the affected side of the face raises
  

Scoring/measuring synkinesis

The most commonly (by surgeons and physicians) used measure of facial range of movement is the House-Brackmann scale.

Unfortunately, this does not have a rating for the aberrant linking of movements which occur in synkinesis.

The Sunnybrook Facial Grading System is a more comprehensive scoring system for facial range of movement, has a section dedicated to rating the presence of synkinesis movements.

Management / Interventions

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Differential Diagnosis

Synkinesis is a clinical diagnosis, and is usually easy to diagnose as the patient will demonstrate clear linking of facial movements on the affected side only and will have a history of facial palsy.

Resources

The Facial Palsy UK charity has a comprehensive website, and this is the page explaining moe about synkinesis.

Case Studies

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References

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