Synkinesis, a term derived from the prefix “syn-,” meaning together with, and the word “kinesis,” meaning movement, refers to a condition wherein involuntary muscular movements occur simultaneously with volitional movements. This condition most commonly results from nerve trauma, which may be precipitated by inflammation, physical trauma, neuroma, or surgery. When the healing of a nerve injury is aberrant, miswiring of nerves occurs and nerve endings innervate muscles that they normally would not stimulate. As a result, when these nerve endings receive a command for voluntary movement the miswired nerves also induce involuntary movement. Treatment modalities for this condition include surgery, facial retraining, Botox, mime therapy, and biofeedback.
The two most commonly studied cases of this condition are facial synkinesis and extraocular muscle synkinesis. Facial synkinesis is one of the most problematic sequelae of Bell’s palsy or idiopathic facial nerve paralysis. Bell’s palsy results from the compression of the facial nerve or cranial nerve VII. During the acute course of this illness, the facial nerve becomes nonfunctional, resulting in a unilateral paralysis of the face. Nerve miswiring occurs as healing takes place, leading to synkinetic symptoms such as involuntary closure of the eyes when pouting or smiling, involuntary midfacial movement with intentional eye closure, neck tightness with voluntary smiling, and hyperlacrimation during eating.
In extraocular muscle synkinesis, trauma to any two of cranial nerves III, IV, and VI leads to simultaneous voluntary and involuntary movements of the six different extraocular muscles. Cranial nerve III or the oculomotor nerve innervates medial rectus, inferior oblique, inferior rectus, and superior rectus. While cranial nerve IV, the trochlear nerve, innervates the superior oblique, cranial nerve VI, the abducens nerve, innervates the lateral rectus. In extraocular synkinesis involving the abducens and oculomotor nerves, when a person tries to look laterally using the affected eye, the eye looks toward the midline and the eyelid retracts. Other types involve the trigeminal nerve and abducens nerve, and the trigeminal nerve and facial nerve.
Symptoms of synkinesis can be quite distressing, so many people consult a doctor to seek permanent relief. Facial retraining is a conservative treatment modality that focuses on teaching how to actively control facial movements. Biofeedback therapy works in a similar manner, and the combination of biofeedback and facial retraining has synergistic effects. Botox, a reversible treatment that involves the injection of botulinum toxin, has been shown to reduce facial hyperkinesis and hyperlacrimation.
Surgical modalities are rarely used and are reserved for patients who do not respond to the aforementioned conservative treatments. One such modality is called neurolysis, wherein the involved nerve is destroyed. Neurolysis does not provide permanent relief, and symptoms often recur in a worse manner. Another surgical modality is selective myotomy, wherein a synkinetic muscle is resected. This provides a more permanent relief compared to neurolysis, but has many complications including edema and bleeding.