Pathophysiology of Synkinesis

Dr. Kedar Adour was fond of saying that contracture and synkinesis follow facial nerve degeneration and regeneration as day follows night (personal communication). In other words, patients who develop a complete facial paralysis invariably have some element of these undesired facial movements. Patients on the other hand who, for whatever reason (viral, trauma, surgery), develop an incomplete acute facial paralysis almost never develop hyperactive facial nerve features.

The three leading theories on why the movements occur are either ephaptic transmission between adjacent nerves, aberrant fiber regeneration, or changes at the facial nerve nucleus. In 1996, Moran and Neely analyzed 11 consecutive patients with abnormal movements looking for insight into which of these three theories was most tenable. Looking closely at the common reproducible patterns of synkinetic movement showed that mouth synkinesis from voluntarily eyelid closure was present universally. In addition, they had cases where the synkinetic activity occurred too quickly to have arisen from fiber regeneration. The repetitive nature of the patterns of synkinesis and speed at which they occur suggested that something occurring at the facial nerve nucleus was more likely or was occurring in addition to the more popular theory of aberrant fiber regeneration.1 These synkinetic movements are of incredible concern to the patient and rank above facial paresis in their societal impact.2

After facial nerve lesions occur with regeneration, the topography of the facial nerve nucleus is disturbed as demonstrated by horseradish peroxidase studies.3 In the rat model, clearly in addition to the regenerating facial nucleus, there is an increased number of collateral branches peripherally.4 In the rat, the possibility of ephaptic transmission (the direct electrical excitability of adjacent intact neurons and even cortical effects of unwanted facial movements) is difficult to prove or disprove at this point.

Hyperexcitability of the nerve may also occur without degeneration and regeneration as the initial phases of irritated lesion. It is well known that slowly compressive noninvasive lesions such as cholesteatoma may be accompanied by either weakness or hyperexcitability.

Evaluation of Patients with Hyperkinesis and Synkinesis

A detailed history is critical in approaching a patient with hyperkinesis and synkinesis. The vast majority of patients with these issues have a history that points directly to a diagnosis. Patients who have had trauma with sudden complete facial paralysis or those who have had surgical activity near the facial nerve with complete facial paralysis will give a history suggesting these events as the cause of their unwanted facial movement. Likewise a classic history for a Bell palsy or Ramsay Hunt syndrome is very helpful in understanding the origin of unwanted facial movements. The patient is often confused by the onset of these movements in a period of time after when they believe that their recovery has already occurred. These late manifestations of recovery often suggest to the patient, or referring doctor, a new process at work rather than a late sequela of the original event. It is precisely because these findings are late that mandates that evaluation and classification of recovery after facial paralysis wait at least 6 months because of the possibility that the degree of synkinesis will change their classification. The treating physician is wise to remember that any intervention along this normal time course can find the physician being blamed for increased hyperkinetic activity after their intervention (surgery, botulinum neurotoxin, etc.) even though the patient is actually experiencing the normal history of facial nerve recovery.

Other disorders that cause hyperkinesis should be mentioned so that the treating physician has awareness. Blepharospasm is a bilateral involuntarily intermittent spasmodic closure of the eyelids. This generally involves the entire orbicularis oculi muscle and the pretarsal, preseptal, and preorbital parts, and usually involves the procerus and corrugator muscles as well. The bilateral nature of the disorder as well as the electromyography findings of synchronous firing at a normal discharge rate generally makes the diagnosis easy.5

Patients with blepharospasm can have other muscles of the face involved. This was documented in a painting by the famed Flemish artist Brueghel who painted a woman with facial and neck involvement, and the term “Brueghel syndrome” is used when extensive lower facial involvement is a major component of the disease. In addition, in 1910 Henry Meige, a French neurologist, described the condition characterized by blepharospasm and facial, mandibular, oral, lingual, and laryngeal spasm. This disease includes involuntary chewing, trismus, lip pursing, wide opening of the mouth, jaw deviation, and tongue protrusion, and is known as Meige syndrome. All of these disorders, blepharospasm, Brueghel syndrome, and Meige syndrome, are part of the spectrum of facial dystonia.5

Blepharospasm is a disease that preferentially strikes middle-aged women. Essential blepharospasm is when the disorder exclusively involves bilateral muscles around the eye and spares the rest of the face. May considered the sine qua non of central blepharospasm where the eyes are clamped tightly shut rather than just blinking or twitching.5 Three-quarters of patients who have blepharospasm will eventually have some lower facial dystonia as well.

A careful drug history should be obtained because dopamine stimulators, nasal antihistamines, decongestants, and patients on long-term neuroleptic treatment can have some of these facial movements as well. Hemi-facial spasm and its management are discussed in Chapters 17.

Patients with synkinesis make up the majority of patients presenting to a facial nerve center for evaluation and management of facial movement disorders. The synkinetic movements can be barely noticeable or completely disfiguring. Although early reports of synkinetic activity have occurred,2 most patients do not begin to have synkinetic movements before 6 months of degeneration and regeneration. The abnormal movements should be only on the side of initial injury. The hyperkinetic problems are generally a deepening of the nasal labial fold due to shortening of the lip elevators, relative closing of the ipsilateral eye due to increased tension in the circular obicularis oculi, and movement of the mouth with eye closure. More infrequently, patients will have sustained platysma spasm and even brow elevation.

The patient should be questioned extensively about what his or her main concerns are. Specifically, situations that are most difficult functionally when they are affected by synkinetic activity should be explored. Patients should have discussion of difficulty with mastication, reading, and driving, especially at night where oncoming headlights can cause complete involuntary eye closure of the affected eye. In addition, any hobbies or work-related limitations caused by the synkinesis should be documented.