Synkinesien

Synkinesien, also known as synkinesis in many medical contexts, is a neurological condition in which voluntary movements are accompanied by involuntary, linked movements in related muscles. The term is most often used in relation to recovery after facial nerve damage (cranial nerve VII), where regenerating nerve fibers reinnervate multiple facial muscles. As a result, actions intended to activate a single muscle can trigger a coordinated but inappropriate contraction of nearby muscles.

Causes and pathophysiology

Most cases occur after acute facial nerve palsy, such as Bell’s palsy or surgical trauma. Less commonly, other causes of facial nerve injury or central nervous system changes can contribute. The underlying mechanism involves misrouting of regenerating axons, leading to co-activation of muscles that normally act independently. Additional factors may include ephaptic transmission between nerve fibers and cortical or peripheral plasticity that reinforces maladaptive movement patterns.

Symptoms and diagnosis

Symptoms typically include involuntary movements of non-target facial muscles during a voluntary action. Examples include eyelid squeezing triggering mouth movement, or a smile accompanied by eye narrowing. Diagnosis is primarily clinical, based on observation of abnormal movement patterns during facial tasks. Electromyography (EMG) can support the diagnosis by showing synkinetic co-activation. Grading systems for facial function may include a synkinesis component.

Treatment and prognosis

Management often centers on botulinum toxin injections to selectively weaken overactive synkinetic muscles, with effects lasting several months and requiring repeated treatment. Physical therapy and neuromuscular retraining aim to improve voluntary control and reduce co-activation. In refractory cases, surgical or reinnervation approaches may be considered. Prognosis varies; many individuals improve with targeted therapy, while others experience persistent synkinesis for extended periods.