Facial Nerve Paresis (Paralysis) in Dogs

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Facial Nerve Paresis (Paralysis) in Dogs

By: Dr. Erika de Papp

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Section: Veterinary Care In-depth

Diagnosis In-depth

A thorough history and physical exam are imperative in establishing the diagnosis of facial nerve paralysis. The diagnosis itself is made based on the physical exam findings, but as discussed, there are multiple underlying disease processes that must be ruled out. A complete history may provide valuable information that will guide the diagnostic evaluation.

Complete blood count. The CBC provides information regarding red blood cells, white blood cells and platelets. An elevation in the white blood cell count may be a sign of inflammation, as might be seen in cases of ear infections and inflammatory CNS disease. Idiopathic facial nerve paralysis does not usually cause significant alterations in the CBC.

Biochemical profile. The biochemical profile is also useful to rule out underlying disease processes. Elevations in blood cholesterol levels may be seen in dogs with hypothyroidism.

Hypoglycemia (low blood sugar) occurs secondary to insulinomas. Other biochemical abnormalities may be an indication of systemic (widespread) disease.

Otoscopic exam. Every patient that presents with facial nerve paralysis should have a careful exam of both ears with an otoscope. This may reveal disease of the external ear canal. The tympanic membrane (eardrum) can also be evaluated via this method. An inflamed or missing tympanic membrane may be suggestive of disease of the middle ear, as the membrane separates the external ear from the middle ear.

Thyroid function evaluation. Hypothyroidism has been implicated in many nerve disorders, including facial nerve paralysis. For this reason, it is advisable to evaluate thyroid levels in any dog with facial nerve disease. Controversy exists as to whether there is a true correlation between facial nerve paralysis and hypothyroidism, but it is worthwhile evaluating thyroid status to be complete.

Schirmer tear test and ocular exam. The Schirmer tear test evaluates tear production. Some animals with facial nerve paralysis will have decreased tear production because the facial nerve supplies the tear producing glands. It is important to evaluate this, as the eye can become damaged if tear production is reduced. A thorough ocular exam is also warranted, because many animals suffer from exposure damage to the cornea when they cannot close their eyelids. This may result in inflammation, ocular discharge, secondary infection and corneal ulceration.

Radiographs or CT/MRI of the middle/inner ear and/or brain. If there is a suspicion of otitis media-interna or primary CNS disease based on the history and physical exam findings, imaging of the middle and inner ear and/or the brain may be indicated. Ear disease can often be missed on routine radiographs. More advanced imaging modalities such as CT or MRI may be needed to evaluate the middle ear more thoroughly, and must be used to evaluate the brain. If the physical exam reveals only facial nerve paralysis, it is unlikely that radiographs or sophisticated imaging techniques will provide further information. If CT or MRI is deemed necessary, this must be performed by a veterinary specialist.

Thoracic radiographs. If there is evidence of a tumor associated with the ear, chest radiographs are indicated to look for evidence of metastatic disease (spread of a primary tumor to the lungs).

Electromyography. EMG is a method to evaluate nerve and muscle function by recording the electrical activity of muscles. This may be useful in cases where a polyneuropathy is suspected, as it aids in evaluating the extent of disease. This is not usually required in cases of facial nerve paralysis without other signs.

CSF tap. The CSF is the fluid that bathes the brain and spinal cord. Analysis of the fluid aids in defining causes of CNS disease. This would only be indicated in cases with physical exam findings consistent with CNS involvement.

Acetylcholine receptor antibody test. This is a specific test that is used to diagnose myasthenia gravis. It would not be valuable in dogs with isolated facial nerve paralysis and no other signs.

Therapy In-depth

There is no specific treatment for facial nerve paralysis. If an underlying cause can be identified, it is imperative that this be addressed and treated appropriately.

Ocular complications of facial nerve paralysis must also be addressed. Any animal with documented facial nerve paralysis and inability to blink should have artificial tears (ointment or drops) administered in the affected eye four times a day, or as prescribed by your veterinarian. Ophthalmic antibiotics may also be required to treat inflammation and/or infection associated with the affected eye. If corneal ulceration develops, it is important that this receive immediate attention, as severe ulceration can lead to permanent ocular damage.

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