Facial Nerve Paresis (Paralysis) in Dogs

Overview of Facial Nerve Paresis (Paralysis) in Dogs

Facial nerve paresis (weakness) or paralysis (total dysfunction) is an abnormality of the facial nerve (7th cranial nerve), resulting in improper function or paralysis of the muscles associated with facial expression. These include the muscles of the ears, lips, eyelids and nose.

In many cases the cause of facial nerve paralysis is idiopathic (unknown). The most commonly identified disease process causing facial nerve paralysis is otitis media-interna (inflammation of the inner and middle ear). Less common, but possible, causes of facial nerve paralysis include:

• Trauma
• Surgery of the ear or surrounding structures
• Neuromuscular diseases
• Polyneuropathies (widespread disease affecting multiple nerves)
• Cancer
• Primary inflammatory diseases of the central nervous system

Facial nerve paralysis occurs in both cats and dogs, but is more common in dogs. Breeds at an increased risk for this disorder include the cocker spaniel, Pembroke Welsh corgi, boxer and English setter. It occurs in adult animals, usually greater than five years of age. There is no apparent gender predilection.

Clinical signs may vary, depending on the underlying cause of the facial nerve paralysis. Usually signs are unilateral (involving one side of the face) but they may be bilateral (involving both sides).

What to Watch For

Signs of facial nerve paralysis in Dogs may include:

• An inability to blink
• Eye discharge or irritation
• Drooping of the lip
• Excessive salivation
• Dropping of food
• Drooping of the ear in dogs with erect (upright) ear conformation
• Slight deviation of the nose to one side
• Head tilt
• Asymmetric pupil size
• Nystagmus (abnormal movement of the eyes)
• Ataxia (uncoordinated gait)
• Generalized weakness
• Asymmetric appearance to the orbital fissures (one eye appears to be opened more widely than the other)

Diagnosis of Facial Nerve Paralysis in Dogs

• History and physical exam
• Complete blood count (CBC)
• Biochemical profile
• Otoscopic (ear) exam
• Thyroid function evaluation
• Schirmer tear test (evaluates tear production)
• Ocular (eye) exam
• Radiographs (X-rays)
• CT Scan or Magnetic Resonance Imaging
• Radiographs of the thorax (chest)
• Electromyography (EMG)
• CSF (cerebrospinal fluid) tap
• Acetylcholine receptor antibody test

Treatment of Facial Nerve Paralysis in Dogs

There is no specific treatment for facial nerve paralysis in dogs. Any underlying disease should be treated. Animals may need to be medicated with eye lubricants to avoid corneal damage. If keratitis (inflammation of the cornea) or corneal ulcers (defects in the cornea) are identified, they must be treated with appropriate ophthalmic antibiotics.

Home Care and Prevention

Application of ophthalmic medications as directed by your veterinarian is important to avoid ocular complications. Follow-up exams with the veterinarian are recommended to evaluate signs of progression or resolution and to maintain close observations of any ocular problems.

For most cases, there is no specific care to reduce the risk of facial nerve paralysis. However, since this is often associated with middle and inner ear disease, it is important to maintain good ear care, especially in animals predisposed to ear disease such as cocker spaniels. This includes careful ear cleaning and immediate veterinary treatment of all ear infections.

In-depth Information on Canine Facial Nerve Paralysis

Idiopathic (unknown cause) facial nerve paralysis is the most common form of the disease in dogs. A large study of dogs with clinical signs consistent with facial nerve paralysis demonstrated an unidentifiable cause of disease in 75 percent of the cases. In idiopathic cases the signs are usually unilateral and there are no other abnormal physical exam or neurologic findings.

In dogs with concurrent otitis media/interna, there may be a history of chronic ear infections or physical evidence of disease associated with the external ear. However, they may not show obvious evidence of ear disease on physical exam, as inflammation confined to the middle and/or inner ear cannot be seen externally.

Evidence of middle and inner ear disease may be demonstrated by additional neurologic deficits seen as abnormalities of the vestibular system (part of the neurologic system that controls balance). These signs might include a head tilt, nystagmus, strabismus (abnormal eye position), and general lack of coordination. Occurrence of facial nerve paralysis and vestibular abnormalities is strongly suggestive of concurrent ear disease, or brain disease affecting the 7th and 8th cranial nerves at their points of origin in the brainstem.

The impact of facial nerve paralysis on your pet depends on whether or not there is an identifiable underlying cause of disease and what other signs are present. Facial nerve paralysis is a physical exam finding and should not be confused with any other disease process, although there are a number of associated causes that must be ruled out, including:

• Otitis media/interna. Another neurologic manifestation of middle ear disease may be Horner’s syndrome. This is an abnormality of the sympathetic nervous system (highly specialized part of the nervous system), which results in a small pupil, raised third eyelid and drooping of the upper eyelid, as well as a sunken appearance to the eye.
• Trauma. Traumatic accidents may cause direct compression of the facial nerve via local tissue swelling or fractures of the skull. In these cases, painful responses to physical examination would likely be noted.
• Surgery. Surgical procedures that are often done to treat chronic (long term) ear disease or to remove ear tumors can result in direct damage to the facial nerve resulting in nerve paralysis. These procedures include ear canal ablation (removal of the external ear canal) and bulla osteotomy (opening of the bony portion of the middle ear).
• Neuromuscular diseases. Diseases in this category affect transmission between the nerves and their associated muscles. Animals with neuromuscular abnormalities will most often demonstrate other signs in addition to facial nerve paralysis such as generalized weakness, as a result of multiple nerve involvement. Examples of neuromuscular diseases include myasthenia gravis and botulism (toxin). Facial nerve paralysis in these cases is often bilateral.
• Cancer. Tumors involving the middle and inner ear may cause direct damage to the facial nerve.
• Polyneuropathies. These are neurologic conditions involving multiple nerves in the body, and may include involvement of the facial nerve. Polyneuropathies may be caused by endocrine diseases such as hypothyroidism, cancerous conditions such as insulinoma (insulin producing pancreatic tumor) and immune mediated processes (diseases in which the body’s immune system attacks its own components, in this case nerve cells). Similar to neuromusclular disease, polyneuropathies generally cause other signs in addition to facial nerve damage, and the facial paralysis may be bilateral.
• Inflammatory diseases of the CNS. Inflammation in the CNS may affect the facial nerve where it originates in the brainstem. If facial paralysis results secondary to a CNS disease, the animal would also likely demonstrate ataxia, behavior changes, possible seizures, and other cranial nerve deficits.

In-depth Information on Diagnosis

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.

In-depth Information on Treatment

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.

Follow-up Care for Dogs with Facial Nerve Paresis (Paralysis)

Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your dog does not rapidly improve. Administer all prescribed medications as directed. Alert your veterinarian if you are having problems treating your dog.

Follow-up exams with your veterinarian are advised to keep track of ocular problems and development of other signs in cases of presumed idiopathic disease, as disease progression may result in the emergence of an underlying cause for the facial nerve paralysis. Additionally, in animals that are being treated for identifiable causes of facial nerve paralysis, response to therapy should be monitored.

Animals with idiopathic disease may recover in three to six weeks, but many animals never recover completely. Most animals tolerate the disorder quite well, as long as the eye is appropriately managed.

Over time, some muscle contracture (shortening) can occur. This may lessen the asymmetry noted in the face, especially in the lips.