What do we do when we see someone whose face is completely paralysed on one side? Most of us would think “stroke” straight away and wonder if their speech has gone too. But not everyone with a facial weakness - or palsy - has had a stroke. Thousands of people each year suffer from what is called bell’s palsy.
In 1828 Charles Bell, after whom the condition was named, first described the functions of the facial nerve. The facial nerve is the 8th of the12 cranial nerves that go straight from the brain to their target organs or muscles. In this respect the cranial nerves are different to all of our other nerves, which reach their target organs/muscles via the spinal column.
In fact, a better name for Mr Bell’s Palsy would be Idiopathic (which means that we doctors don’t have a clue what the cause is) facial paralysis, or IFP, because that tells us far more accurately what the condition actually is.
IFP is what happens when the facial nerve is damaged as it travels from the brain, and when nerves get damaged, they do strange things. The result of this damage is that those muscles supplied by the nerve – in this case it’s the muscles of facial expression on the affected side of the face - will stop working and become paralyzed. If there is any good news, then it’s that IFP will only affect one side of the face - it is extremely rare that both nerves are affected at the same time. But for the sufferer, the sudden appearance of a facial palsy will often make them think “is this a stroke?” The answer lies in the fact that IFP only affects one nerve, the facial nerve: strokes affect an area of the brain and have a much wider impact on the body.
The facial nerve has some very interesting functions as well as making our facial muscles work.
Using the analogy of a telecommunications cable, then inside each nerve/cable are literally thousands of tiny nerve fibres each of which has a very specific function. Most of the nerve fibres in the facial nerve are there to serve the facial muscles that they connect too. But the facial nerve also contains fibres that carry:
- Sensory information from the tongue,
- Touch sensation from a small patch of skin behind the ear,
- Special nerve fibres that help control the salivary and lacrimal/tear glands.
- There’s also a connection to the smallest muscle in the human body - the stapedius muscle.
The stapedius measures about one millimeter in size and is attached to the neck of the smallest human bone, which is called the stapes, but it’s also known as the stirrup. This horseshoe-shaped bone, is part of a chain of small bones which transform the sound-waves that hit the ear drum, into electrical impulses to be sent to the brain. When a loud sound is heard, this skeletal muscle reflexively pulls on the head of the stapes to reduce excessive vibration and to protect the inner ear. When it becomes paralysed, as in IFP, normal sounds can register as extremely loud and uncomfortable and this is known as hyperacusis.
What is the cause of IFP?
The journey that the facial nerve takes to get from the brain to the face requires that it travels through a very narrow canal in the base of the skull - at its narrowest it is a mere 0.66mm in diameter - and it’s here that the cause of IFP is thought to be found. It’s within this tight bony canal that the nerve can become inflamed, causing it to swell: but swelling within solid bone leads to crushing of the nerve itself, and that leads to loss of function. The big question is, what causes the inflammation to occur?
Currently we are not sure what the cause is although there is evidence that points to viral causes such as herpes simplex I. But there is also a long list of other associated causes too and these include herpes zoster, lyme disease, syphilis, Epstein-Barr viral infection, cytomegalovirus, human immunodeficiency virus [HIV] and mycoplasma.
Irrespective of the cause of IFP, the good news is that in the great majority of cases, it will settle of its own accord although this can take weeks to even months. High dose steroids have been found to be of some benefit if used in the first few days after the symptoms first appear.
Whilst the facial paralysis is the most striking result of the disease, it’s the eye on the affected side that can be the major concern. There is a real danger that the affected eye can be permanently damaged because the eyelids no longer fully close, and the tear gland stops functioning too- and this leads to a dry eye syndrome.
Because the surface of the eye gets it’s protection and it’s nutrition from the surface tears, if you lose them and the cornea dries out, then it becomes easily damaged and scarred. So it’s critical that from the word go that the eye gets 24 hour protection. That means constant attention with lubrication eye drops and the use of an effective eye patch at night time.
Bells palsy can be very distressing for the sufferer, and does have the real potential to cause damage to the eye. The great news is that nearly everyone will recover, and the eye come through unscathed if treated correctly.