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
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
- 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
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.