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FACIAL PARALYSIS Note for Pet Owners:
This information is provided by
Provet for educational purposes only.
You should seek the advice of
your veterinarian if your pet is ill as only he or she can correctly advise
on the diagnosis and recommend the treatment that is most appropriate for
your pet. Topics on this Page:
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Description
There are two facial nerves - one on either side of the head, and they are
one of the main nerves leaving the brain - in fact they are called the VII
cranial nerves, and are generally known as the nerves of "facial
expression".
On each side the facial nerve passes near to the ear and around the angle of the jaw (around the mandible) . It carries nerve messages to and from the ear, facial muscles, eyelids, the salivary glands (which produce saliva in the mouth) and lachrymal glands (which produce tears).
The facial nerve carries mixed nerve fibres including :
- Motor neurones - stimulate action in tissues eg stimulate muscle to contract
- Parasympathetic fibres - often stimulate non-life threatening secretions eg saliva, tears
Cause
The cause of facial nerve paralysis is often unknown (called idiopathic facial
paralysis) however, th
- Injury - any blow or wound to the nerve can cause paralysis
- Local pressure on the nerve - eg an adjacent tumour
- Injury to the nerve secondary to middle ear infection
- Hypothyroidism
- As a consequence of Lyme Disease
Breed Occurrence
Hypothyroidism, which can cause facial paralysis, is reported to be particularly prevalent in the following breeds of dog : Akita, Boxer, Cocker Spaniel (American), Collie, Doberman Pinscher, English Setter, German Shepherd Dog, Golden Retriever, Irish Setter, Labrador Retriever, Old English Sheepdog, Shetland Sheepdog. However, autoimmune thyroiditis - one of the most common causes of hypothyroidism is now thought to be an inherited problem in about 50 breeds !
Lyme Disease - is a transmitted by deer ticks, and so it is most common in working field dogs and dogs exercised in countryside frequented by deer.
Signs
The signs of facial nerve paralysis are predictable from a knowledge of the type of nerve fibre it consists of, and the anatomical areas it serves. Paralysis usually only occurs on one side of the face resulting in :
- Loss of muscle tone to facial muscles including eyelids resulting in:
- Drooping of the lip
- Inability to close the eye
- Inability to move the ear
If the facial paralysis is secondary to another disease, signs of that disease might also be present in the same patient eg hypothyroidism, Lyme Disease, ear infection.
Complications
- "Dry eye" due to the lack of tears leading to inflammation of the surface of the eye (the cornea) called keratitis. If this is not corrected ulceration of the cornea may occur
- An inability to blink means that debris including small bits of foreign material are not cleared away from the surface of the eye - again resulting in injury to the cornea
- Lack of saliva leads to dryness of the mouth which may impair eating. However, as the paralysis usually only affects one side, the other salivary glands are probably functioning normally and so lubricate the mouth.
- Paralysis of the facial muscles may lead to difficulty eating (dysphagia)
Diagnosis
Visual examination of the animal by a veterinarian is usually sufficient to
diagnose the presence of facial nerve paralysis.
Diagnostic tests may be needed to confirm the diagnosis of other diseases such as hypothyroidism or Lyme Disease.
Treatment
Facial paralysis may be temporary or permanent. It is most likely to be
permanent if the nerve has been transected, has degenerated or if there is a
primary brain lesion.
Blunt trauma usually causes only temporary paralysis and if the underlying cause is known and treatable eg Lyme Disease, ear infection or hypothyroidism - the patient can be expected to recover in most cases.
Prognosis
Good for most patients
Long term problems
Updated January 2016