Facial Nerve Paralysis

My dog awoke with a droopy upper lip, what could it be?

Dogs get a relatively common condition that is quite similar to Bell’s palsy in humans, called facial nerve paralysis. The facial nerve is an important cranial nerve that sends signals to (innervates) all facial expression muscles, taste buds, and the tear producing gland.

There are several causes of facial nerve paralysis, the most common of which is idiopathic meaning the cause is not known. In fact 75% of the time it is idiopathic. The other cases can be caused by middle ear infections, low thyroid levels, and trauma.

This condition usually occurs in middle aged and older dogs, and particularly in the cocker spaniel. Although not stated in the literature the golden retriever is commonly affected.

This problem usually comes on quickly, and most pet owners notice lip and or ear droop and excessive salivation. Sometimes food can get caught on the lip or fall out of the mouth with this condition. Facial nerve paralysis (FNP) is not painful.

A more subtle feature of FNP is the lack of proper blinking and tear production which can lead to a dry eye. Some patients will develop corneal ulcers.

In diagnosing FNP the veterinarian will perform a neurological exam, blood work including a thyroid test, and tests on the eye to check for tear production and corneal integrity. In some cases an MRI is completed to look at the middle ear and the brainstem, which is the area the cranial nerves originate.

Again the most common cause of FNP is the idiopathic form where no identifiable cause is determined. Hence treatment is supportive rather that directed at a specific cause. One of the key elements of treatment is keeping the eye lubricated with artificial tears. This treatment is usually long term as most of these patients never fully recover. The benefit of corticosteroids is not known in veterinary medicine for this condition, yet corticosteroids can have a positive effect in humans with Bell’s palsy.

Of course patients with middle ear infections or low thyroid levels can be treated specifically. Although hypothyroid dogs may never return to normal relative to the FNP.

As stated the prognosis is poor with this condition, some patients will have a partial recovery and some not at all. Rarely FNP will occur on the opposite side as well. On the positive side, this condition is not a stroke and not a progressive disease. Most FNP dogs proceed to live a normal happy life, albeit with lots of eye drops.