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What Causes Facial Paralysis in Dogs?
Facial paralysis is caused by a variety of conditions that lead to inflammation or damage of the facial nerve, also known as cranial nerve VII. The facial nerve originates at the level of the brain stem and then courses through the temporal bone. It exits the skull and forms three branches near the ear canal that innervate various parts of the face.
Common causes of facial nerve paralysis in dogs include:
Otitis media – Inflammation or infection of the middle ear is a common cause of facial paralysis.
- Trauma – In dogs, overt trauma is not a common cause of facial nerve paralysis. Procedures that may damage the facial nerve are much more likely including total ear canal ablation or removal of tumors from within the inner ear.
- Hypothyroidism – Low levels of thyroid hormones can affect various cranial nerves including the facial nerve in dogs leading to paralysis.
- Idiopathic facial neuritis – Idiopathic is a term used to describe a condition without a known inciting cause. Idiopathic facial neuritis (nerve inflammation) is similar to Bell’s palsy in humans. It typically will cause sudden-onset, unilateral facial nerve paralysis in middle-aged or older dogs.
- Cancer – Tumors of the middle ear can cause damage to the facial nerve, the most common tumors being squamous cell carcinoma and ceruminous gland adenocarcinoma.
Symptoms of Facial Paralysis in Dogs
Clinical signs of facial nerve paralysis depend on the severity, location, and duration of onset. Unilateral facial nerve paralysis is much more common than bilateral. Depending on where the nerve is damaged in its course, various parts of the face may be affected including the ear, eyelid, lips, and nostril.
The most common clinical sign of facial nerve paralysis is the inability to blink on the affected side. The eyelids will be unable to close. Instead, the eye will retract and the third eyelid will become elevated. The ear on the affected side may have a lower carriage. The lips on the affected side will be loose and the dog may drool from that side. Food may collect on the affected side when eating. Dogs can also have reduced tear production which may predispose them to corneal ulceration.
If the facial nerve is diseased at the level of the brainstem, there may be a presence of other neurological deficits including limb weakness, abnormal paw placement, or altered mentation. A disease of the middle ear affecting the facial nerve may cause a head tilt or Horner syndrome.
How is Facial Paralysis in Dogs Diagnosed?
Facial nerve paralysis is diagnosed in a variety of ways. First, your veterinarian will discuss your dog’s background and history. Next, a physical examination will take place. Facial nerve paralysis will be confirmed with a thorough neurological examination. The veterinarian will also perform an otoscopic examination of the ear to assess for signs of infection, inflammation, or masses.
Additional tests may include evaluating thyroid function to rule out hypothyroidism. Advanced imaging may be recommended such as MRI or CT to rule out infectious, inflammatory, or neoplastic causes of facial nerve paralysis. If a tumor is found, a biopsy is recommended for a definitive diagnosis.
Treatment for Facial Paralysis in Dogs
Treatment of facial nerve paralysis is geared towards addressing the underlying cause. Dogs with inner ear infections may require oral and topical antibiotics as well as anti-inflammatory medications. Hypothyroidism is treated with the supplementation of a synthetic thyroid hormone called levothyroxine. Tumors may be addressed with a combination of surgery, chemotherapy, and/or radiation therapy. There is no treatment for idiopathic facial nerve paralysis. Dogs with this condition that have decreased tear production will benefit from daily eye lubrication to prevent the development of corneal ulceration.
Can Dogs Recover from Facial Paralysis?
The likelihood of recovery from facial paralysis in dogs is dependent on the underlying cause. Addressing inner ear infections promptly will improve the chance of recovery, but many cases will result in permanent paralysis. Dogs with hypothyroidism will typically recover facial nerve function within 6-8 weeks of starting thyroid supplementation. Dogs with idiopathic facial nerve paralysis can have partial or complete recovery in weeks to months, though some dogs can progress to bilateral paralysis.
If the nerve paralysis is permanent, the affected side of the face may experience muscle contracture and fibrosis. This will cause the lips to become permanently pulled back, deviation of the nose, and a higher ear carriage on the affected side of the face. Dogs will typically continue to live normal lives with minimal secondary consequences of the condition.
Facial nerve paralysis is diagnosed by observation of classic clinical signs including the inability to blink, facial/lip drooping, and lower ear carriage on the affected side.
Facial paralysis can last for varying durations depending on the underlying cause. Dogs with hypothyroidism will improve in 6-8 weeks after starting medication. Dogs with inner ear disease may have recovery over several weeks to months or even suffer from permanent paralysis. Animals with idiopathic facial nerve paralysis generally recover within a few months.
Dogs with facial nerve paralysis secondary to hypothyroidism or idiopathic causes are not painful. Dogs with inner ear infections, tumors, or trauma are typically in pain until the underlying cause is addressed.