Peripheral facial paralysis refers to paralysis that manifests in all areas of the face, from the forehead to the mouth. It is usually unilateral, more rarely bilateral. In most cases, the cause of the paralysis is unknown and the condition is called Bell’s Palsy. The incidence of Bell’s Palsy is 20–30 per 100,000 per annum.
Most people who suffer from Bell’s Palsy make a good recovery, but an estimated 30 per cent of patients are left with mild or moderate after-effects.
Botulinum can be used to improve facial symmetry in patients who have suffered from peripheral facial paralysis. The treatment improves both the functionality and appearance of the face.
Synkinesis is a common after-symptom in patients who do not fully recover from peripheral facial paralysis. It is manifested through involuntary muscular contractions accompanying voluntary movements. One of the most common is a closing of the eye on the affected side in conjunction with mouth movements. The eye may even close completely when the patient is eating or laughing. Another common involuntary movement involves the cheek and corner of the mouth on the affected side – they are pulled upwards when the patient closes his or her eyes. Involuntary movements may also manifest as after-effects in patients who have successfully recovered facial muscular function. Sometimes, involuntary movements may further reduce facial muscular function in patients whose muscular function has only partially returned to normal.
Botulinum can reduce involuntary movements by preventing the affected muscles from functioning. Botulinum is injected around the eye to prevent the eyelid from closing. The injected doses are initially small, as the paralysed or partially regenerated nerve’s response cannot be predicted in advance. The dosage is then adjusted so that the response is sufficient to reduce involuntary movements yet not large enough to hinder eyelid function. Although involuntary movements may not be completely prevented, the patient’s quality of life will usually improve, as their symptoms will be alleviated and their eyes will not close so much during mouth movements.
Treating involuntary movements of the cheek and corner of the mouth is more challenging, as the botulinum doses required to reduce involuntary movements easily weaken function as well. Even though it may improve the patient’s appearance, the final result may be worse in terms of functionality. The strength and obtrusiveness of the patient’s involuntary movements usually determine what risk of functional weakness the patient is willing to endure as a consequence of botulinum injections.
Muscular contractions are an after-symptom of paralysis that may affect the cheek area. The cheek pulls upwards and the fold between the nose and corner of the mouth deepens. These can also be eased with botulinum, but potentially weakened functionality in the upper lip and corner of the mouth must be considered. Post-paralysis contractions of the platysma muscle in the neck are a good candidate for botulinum, as the doses required to treat the tightened fascicles do not affect neck functionality.
Another after-symptom of facial paralysis in addition to involuntary movements and contractions is the hemifacial spasm, that is, involuntary muscle twitches. These usually manifest around the eyes, cheeks, corners of the mouth, and chin. Botulinum can be injected to treat twitches in these areas. Many patients also develop dimples in the chin on the affected side, and they are particularly evident when smiling. These dimples are easily treated with botulinum, as the required dose is usually small and the response good without leading to any functional weakness.
Some facial paralysis patients shed tears on the affected side when eating (crocodile tears). Injecting botulinum into the tear gland can reduce tear production and ease symptoms.
If the patient does not make a full recovery from facial paralysis, the healthy side may try to overcompensate for the paralysed side. This hyperfunction increases asymmetry and often hinders overall facial functionality, and patients feel their face to be under increased stress. Botulinum can reduce hyperfunction. Normal injection sites are the forehead (well above the eyebrow on the healthy side, forehead wrinkles on the healthy side only); the cheek, upper section of the fold between the nose and the corner of the mouth (the cheek and above the corner of the mouth on the healthy side, the nose is pulled to one side), and around the mouth (crooked smile, teeth more visible on the healthy side than the affected side when smiling and speaking). These same injection sites can be used for patients who are not experiencing hyperfunction in their healthy side but are aesthetically bothered by asymmetry.
The unit doses of botulinum used to treat facial paralysis are small and no serious side effects have been described in the literature. The most common side effects are the aforementioned temporary functional weakness and localised bruising and redness at injection sites.
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