Synkinesis is a condition of involuntary and simultaneous facial movements that develop after a facial nerve injury. The term means “simultaneous movement,” describing a situation where an intended action in one part of the face triggers an unwanted movement in another area. This complication frequently arises during recovery from facial paralysis, such as after Bell’s Palsy or following surgical procedures near the nerve. The condition indicates the facial nerve, which controls expression muscles, has regenerated in a disorganized way. Synkinesis can affect a person’s quality of life by causing facial tightness, fatigue, and noticeable asymmetry.
The Neurological Cause of Synkinesis
Synkinesis is a consequence of aberrant nerve regeneration following injury to the facial nerve. When the facial nerve is damaged, the axons are disrupted, leading to paralysis of the facial muscles. Over time, these damaged axons attempt to regrow, a process known as axonal sprouting.
The issue arises because the regenerating axons do not always find their original muscle targets. For instance, an axon destined for the mouth might mistakenly reinnervate the muscles around the eye. This “miswiring” means a single signal from the brain intended for one movement, like a smile, is accidentally delivered to multiple muscle groups.
Many axons develop several sprouts and regrow randomly into different peripheral facial nerve branches. This collateral sprouting results in a single nerve fiber sending branches to the muscle fibers of two or more different muscles. When the brain sends a command for a voluntary movement, the signal travels down the misdirected nerve, causing the simultaneous contraction of unintended muscles. This misdirection often causes patients to experience constant tightness or increased muscle tone on the affected side, even at rest.
Recognizing Common Synkinesis Patterns
The visible manifestations of synkinesis are characterized by predictable patterns of linked, involuntary muscle contractions. A common pattern is ocular-oral synkinesis, where voluntary movement of the mouth (such as smiling or speaking) causes the eye on the affected side to narrow or partially close. This unwanted eye closure is a primary symptom patients notice.
Another frequent presentation is oral-ocular synkinesis, where actions like forcefully closing the eye or raising the eyebrow cause the corner of the mouth to pull upward. Patients often experience platysmal synkinesis, involving involuntary tightening or banding of the neck muscles during facial movements. This neck tightening restricts the ability to achieve a full smile and may pull the corner of the mouth downward.
A specific, less common type is gustatory lacrimation, sometimes called “Crocodile Tears.” This occurs when a person eats or chews, and the stimulus of salivation mistakenly triggers the tear glands to produce tears, resulting in involuntary watering of the eye. These linked movements also contribute to a deepening of the nasolabial fold, or smile line, on the affected side due to continuous muscle overactivity.
Current Treatment Strategies
The management of synkinesis focuses on a multi-modal approach aimed at reducing involuntary movements and retraining the brain’s control over the facial muscles. Neuromodulation using Botulinum Toxin type A (Botox) is a primary and highly effective treatment. Botox temporarily weakens the hyperactive, synkinetic muscles (such as those around the eye or in the neck) to reduce their involuntary contraction. The injections are precisely targeted to the overworking muscles, like the orbicularis oculi or the platysma, to restore better balance and symmetry. This chemodenervation procedure is typically administered every three to four months to maintain the therapeutic effect.
Physical therapy, specifically facial neuromuscular retraining, is an equally important component of treatment. This specialized rehabilitation involves targeted exercises focused on relaxation, isolated movement practice, and biofeedback. The goal is to teach the brain to consciously control the affected muscles separately, inhibiting the unwanted, linked movements. Neuromuscular retraining combined with Botox injections significantly improves facial function and reduces the severity of synkinesis symptoms.
For patients with severe synkinesis that does not adequately respond to non-invasive methods, surgical interventions may be considered. These procedures include selective neurectomy (cutting specific nerve branches to relax tight muscles) or myectomy (removal of small, dysfunctional muscle segments). These surgical options are highly individualized and are typically preceded by diagnostic nerve blocks to predict the potential outcome.