Facial weakness (palsy)
The facial nerve, also known as the seventh cranial nerve, innervates the muscles of facial expression. These include the muscles that raise the eyebrows, blink and close the eyes and control the mouth/jaw. The nerve starts just below the brain, in the brainstem, and has a relatively long path via the inner ear and parotid gland before branching across the face.
Conditions which do not directly affect the nerve, but rather interfere with the parts of the brain/brainstem which control the nerve, cause an "upper motor neuron facial weakness" eg:
- brain tumour,
- multiple sclerosis.
Diseases which directly damage the nerve itself result in a "lower motor neuron facial weakness" eg:
- Bell's palsy
- Infections like shingles (Ramsay Hunt sundrome)
- Inflammatory conditions such as sarcoidosis
- Tumours eg: parotid gland mass, mengioma
Bell's palsy is the commonest cause of a facial weakness, accounting for up to 70% of all cases. Anyone can be affected but the peak age group is between 15-45 years. The facial weakness usually develops over about 24 hours and the affected individual may notice difficulty closing the eye on that side and problems with eating or drooling.
The cause of Bell's palsy remains unknown but it appears to be due to an inflammation in the facial nerve. If the patient is seen within a few days of the problem starting steroid tablets (prednisolone) are often prescribed, to be used for 7-10 days. This treatment probably results in a quicker recovery, although research suggests that the "final recovery" after 12 months is no different to cases where steroids were not used. There is a suggestion that the herpes simplex ("cold sore") virus may be involved in causing Bell's palsy and there is weak evidence that using the oral anti-viral tablets - acyclovir may be beneficial.
Eighty percent of people with Bell's palsy start to recover within the first 3 weeks of being affected. Complete recovery, or only mild residual weakness, occurs in 90% by 6 months.
What are the effects of a facial weakness?
As the facial nerve supplies so many of the muscles in the face there are many possible consequences of the nerve malfunctioning. Working from the upper face downwards these include:
- Droopy eyebrow (brow ptosis).
- Upper eyelid retraction (eye more open than unaffected side).
- Slow, incomplete blinking.
- Inability to close eye.
- Lower lid drop and/or ectropion (see ECTROPION).
- Sagging of the corner of the mouth which affects speech, drinking and eating.
Treatment of facial weakness
The main priority initially is to protect the eye as reduced blinking and closure can rarely be sight threatening. The surface of the eye can get extremely dry very quickly, making the eye prone to infection and serious corneal ulcers.
Various simple measures can immediately help to improve the situation:
- Regular use throughout the day of a topical lubricating drop or gel.
- Ensuring the eye is protected at night either by using tape (or eye pads) to close the eyelids or a thick ointment liberally applied over the eye surface.
- Botulinum toxin (see BOTULINUM TOXIN section) can be injected into the upper eyelid in order to temporarily close the eye (ptosis) and protect the ocular surface. This can be extremely useful in some situations, the effect usually wearing off in 6 weeks by which time there may be some recovery of facial nerve function.
Some patients, especially when it is known that the facial weakness is unlikely to recover, require surgery. There are various oculoplastic procedures which can be helpful in protecting the eye, improving function, reducing watering and re-establishing upper facial symmetry. Commonly patients require a combination of surgical techniques from a list which includes:
- Eyebrow lift
This involves raising the dropped eyebrow, usually via a wound just above the brow hairs, and fixing the brow higher up to match the unaffected side. This often improves peripheral vision and symmetry.
- Upper lid lowering/Gold weights
Lowering the upper eyelid, either by weakening the levator muscle which elevates the lid or by inserting a gold weight into the lid, improves blinking and eyelid closure. Platinum chain weights can be used in cases of gold allergy.
- Lower eyelid ectropion correction(see ECTROPION)
The paralysed lower eyelid can be tightened and elevated back into contact with the eye surface. Often this needs to be done in the inner corner (medial canthoplasty) and at the outer aspect of the lid (lateral tarsal strip).
Occasionally it may be beneficial to suture the eyelids together, either centrally (central tarsorrhaphy) or at the outer edge (lateral tarsorrhaphy). This can be performed using a temporary or permanent technique. I rarely use this relatively old-fashion method of protecting the eye as usually there are other options which work just as effectively with a better cosmetic result.
Finally a small number of people develop problems secondary to aberrant regeneration of the facial nerve. This is also known as facial synkinesis and is the result of facial nerve miswiring. The nerve tries to recover and regenerate, but ends up supplying the wrong facial muscles. This can cause the eyelids to spasm and close involuntarily, or the unusual situation whereby tears are produced when eating ("crocodile tears"). Botulinum toxin (see BOTULINUM TOXIN section) can be useful for treating these abnormal facial conditions.