Facial Nerve Paresis/Paralysis in Dogs

 

Facial nerve paresis is a dysfunction of the seventh cranial nerve, the facial nerve. This condition is evidenced by paralysis or weakness of the muscles of the ears, eyelids, lips, and nostrils.

 

The cause of this disease is impairment of the facial nerve, or of the place where the nerves come together, and it affects the electrical impulses of the nerves involved. The facial nerve is affected, and sometimes the ophthalmic system as well, interfering with the function of the tear glands. Dry eye syndrome also accompanies the tear gland interference. Gender does not play a role, but breed appears to in some cases. Adult age Cocker Spaniels, Pembroke Welsh corgis, boxers, and English setters are most likely to experience this condition.

 

Symptoms and Types

 

• Messy eating; food left around mouth
• Food falling from the side of the mouth
• Excessive drooling
• Inability to close eye; rubbing; discharge from eye
• Inability to close the eyelids
• Wide separation between the upper and lower eyelids
• Decreased or absent menace response and eyelid reflex
• Facial asymmetry
• Ear and lip drooping
• Collapse of the nostril
• Chronic - patient may have deviation of the face toward the affected side
• Occasional facial spasms may be observed
• Discharge of pus from the affected eye
• Somnolence or stupor

 

Causes

 

One sided facial nerve paresis:

• Idiopathic (unknown cause)
• Metabolic - hypothyroid
• Inflammatory - otitis media-interna: inflammation of the inner ear
• Nasopharyngeal polyps: benign growths that can occur in the back of the throat, the middle ear and even perforate through the ear drum – rare in dogs
• Cancer
• Trauma - fracture of a bone at the base of the skull; injury to the facial nerve
• Iatrogenic (physician induced) - secondary to surgical flushing of the external ear canal

 

Two-sided facial nerve paresis:

• Idiopathic - rare
• Inflammatory and immune mediated - inflammation of nerve roots, including coonhound paralysis; polyneuropathies (multiple nerves are involved); myasthenia gravis (muscle weakness)
• Metabolic - nerves affected by cancer in the body
• Toxic - botulism
• Pituitary neoplasm: abnormal tissue growth – of unknown cause
• Infectious - Lyme disease in humans not proven in dogs at this time

 

Central Nervous System:

• Most are one-sided
• Inflammatory - infectious and noninfectious
• Neoplastic - primary brain tumor; metastatic tumor

 

 

 

Diagnosis

 

You will need to give a thorough history of your dog's health, onset of symptoms, and possible incidents that might have preceded this condition.

 

Your veterinarian will first determine whether the paresis is one sided or both sided, and will then look for other neurological signs. Unless your dog has had an ear disease, or other neurological deficits, the cause will be determined as unknown. Some of the causes that will be considered will be possible middle or inner ear disease; if your dog is lethargic and has a poor hair coat, a test for hypothyroidism will be done; if your dog is sleeping a lot and is displaying symptoms related to a brainstem disorder, a disease of the central nervous system will be considered.

 

A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis, although these are typically normal in the case of facial paralysis. Even so, there are some disorders that might account for the symptoms, such as an anemia, excessive production of cholesterol, or low blood sugar.

 

X-rays, computed tomography (CT) scans, or magnetic resonance imaging (MRI) may be used to detect the location of the problem. There are also other tests that can be used to evaluate tear production, motor nerve conduction speed, and for the detection of brainstem disease.

 

Treatment

 

Treatment will most likely be on an outpatient basis, but your veterinarian may need to hospitalize your dog for the testing procedures. If fiber develops in the muscles, there is a natural tuck up that reduces asymmetry, and drooling usually stops within two to four weeks. But, you will need to be prepared for the possibility of the clinical signs remaining permanently, or returning. In addition, the other side of the face can become affected. The cornea on the affected side may need long term lubrication, and extra care may be needed if your dog is a breed with natural bulging of the eye. You will also need to regularly check for corneal ulcers. Most animals tolerate this nerve deficit well, but if the disorder is in the middle ear, surgery may be necessary for relieving the severity of the discomfort.

 

Living and Management

 

Your veterinarian will want to reevaluate your dog's condition soon after the initial treatment for evidence of superficial loss of tissue on the surface of the cornea. If there is a corneal ulcer your dog will need to be seen frequently for treatment. After that, your dog will be assessed monthly for reflexes of the eye and eyelids, lip and ear movements, and to evaluate the return of normal function.

 

Eye care: the cornea on the affected side may need frequent lubrication or application of artificial tears. Most animals tolerate this nerve deficit well.