Facial Nerve Paresis (Paralysis) in Dogs

This paresis (milder dysfunction) or paralysis (more severe dysfunction) can occur only one side of the face (unilateral) or both sides (bilateral) and can range in severity from mild to moderate to severe. It can have a short duration or long term or permanent dysfunction.

Facial nerve paresis or paralysis is the inability to move eyelids, ears, lips or nostrils as a result of various types of damage to the facial nerve or nucleus. This damage causes the muscles to lose tone and inhibits their ability to move and function as designed.

How might you tell if your dog is suffering from facial nerve paresis or paralysis? If the paresis or paralysis is unilateral, the appearance of your dog’s face will be asymmetrical - that is the two sides of his face will not look the same. If the paresis or paralysis is bilateral, your dog will have a dull facial expression and increased drooling. When both sides look similar, it makes the diagnosis a bit more difficult but not impossible. Here are some of the symptoms you would likely notice to some degree in your pet if a unilateral paresis or paralysis is present:

• Inability to move the eyelids causing problems in the blinking process or to close normally
• Ear set or carriage may appear higher or lower on one side than the other side
• Lips may droop or sag, exposing the mucosa and allowing food and drinks to leak or fall out of your pet’s mouth
• Nostrils may not be symmetrical in that one nostril may deviate toward one side or the other
• The palpebral fissure (the eye opening) may be larger on one side than the other
• If the lateral or medial (nasal or temporal) corners of the palpebral fissure are touched, the eyelid may not close but the eyeball will likely retract into the orbit instead, due to the lack of mobility of the frontalis muscle in the upper eyelid
• The third eyelid may even elevate in some instances
• If the lips are drooping, you will likely notice food caught between the lips and teeth of your pet.
• Reduced salivation or tearing on one side

Types

• Complete facial paralysis which is the inability to move the eyelids, ears, lips and nostrils of the dog; this is the more severe of the two types
• Facial paresis is a milder form of facial paralysis in that some movement of the eyelids, ears, lips and/or nostrils is possible but the movement is reduced

These two types are dependent upon the degree to which the facial nucleus or nerve is involved, both in terms of damage or injury and location. The nucleus of the facial nerve, also known as cranial nerve VII, is located in the rostral medulla oblongata of the brain stem and it travels various bones and pathways until it ultimately exits the skull through the stylomastoid foramen and then splits into auricular (ear), palpebral (eye) and buccal (lips) branches.

Unlike the human counterpart, facial nerve paresis is not due to any disease of the brain in most dogs. It is usually caused by something that has damaged the facial nerve itself and this damage affects the way in which the nerve causes its associated muscles to behave, or not behave. And this nerve travels from the back of the brain to cause some of above symptoms in Fido or Fifi so they don’t look and act quite like themselves. Here are some of the causes to look for:

• Idiopathic facial nerve paresis basically means there really is no known cause for its sudden onset; it could be compared to a human condition known as Bell’s Palsy
• Otitis media/interna is a chronic, deep ear infection; if you’re aware of Horner’s Syndrome in humans, then you may also see symptoms like decreased pupil size, third eyelid coming over eye, head tilted to one side or the other, and a problem with maintaining balance
• It is rare that facial nerve paresis in dogs is linked to diseases that affect multiple nerves or brain disease
• Trauma or rough handling is another cause of facial nerve paresis, this can come in the form of some type of accident, or rough playing or even abuse

Once damage from trauma, infection or lesion has occurred, the nerve impulses to various muscles get mixed up and the muscles can’t behave as designed. The muscles lose tone and the sagging and drooping of facial muscles, the changes in your pet’s facial appearance are the result.

Your veterinarian will need to do some testing before he or she can ascertain the cause of the facial paresis or paralysis. A physical examination of the dog will need to be performed to determine which muscles and areas of the face are being affected and if the paresis or paralysis is limited to only one side or if it involves the whole face of your pet. Knowing the involvement of the various parts of the facial structure will help him pin down the location of the injury or damage to the nerve. 

Since deep ear infections are a common cause, the veterinarian will need to do a thorough ear examination using a scope to look at the ear canals and ear drums to ascertain any abnormalities. He will be looking for signs of a ruptured ear drum or inflammation of the ear canal. This may need to be done under anesthesia or some sort of sedation.

Specialized imaging like x-rays of the skull, CT scans and MRI of the rear part of the brain are also used to determine if there are any suspicious lesions or swelling that could be causing the facial paresis or paralysis. A sample of the fluid around the brain may be needed to test for inflammation. Blood work will also likely be needed to determine potential for infection and inflammation.

Your veterinarian will need information from you like when did you notice the paresis, paralysis, drooling and other symptoms noted above. Did the symptoms seem to be of sudden or gradual onset? Has your pet experienced any trauma recently? He will want to know if you have noticed any behavioral changes and how long those changes have been present.

Once your veterinarian has performed the testing to obtain a diagnosis, even if it is a preliminary one, he will need to re-evaluate your pet periodically to assess adequacy of treatment, if any, as well as how the condition is progressing, whether worsening or improving. There will likely be several follow up appointments needed depending on how your pet responds to treatment and the severity of the paresis or paralysis. 

If an ear infection is determined as the cause, then he or she would need to treat that with a regimen of antibiotics that could be required for 4 to 6 weeks. If your pet doesn’t respond to treatment, a recommendation for surgical draining of the ear could be proposed. 

If the cause of the facial paresis or paralysis is determined to be idiopathic (no known cause found), then no treatment will likely be initiated.

Frequently, the signs and symptoms noted about are permanent, no matter what the treatment. But the long term effect on your dog’s quality of life is usually not significant. If no underlying problem was found for the nerve damage, then your pet’s prognosis or outlook is good. That droopy lip that caused the salivation, dropping of food and floppiness to the lip will be replaced with more chronic signs such as the return of the lip to its normal size and shape though it will still be unable to move as it is did previously.

In the case of the ear infection as the cause for the facial paresis or paralysis, you will have to remain more watchful as chronic ear infections can cause irreversible and permanent nerve damage and paralysis.

Always be watchful, however, as potential exists that, if the paresis or paralysis was unilateral, it could go away and present later on the other side.