Facial paralysis in dogs may result from injuries caused by rough handling or other trauma, such as automobile accidents, inner ear infections, hypothyroidism, tumors, and unknown causes. Paralysis on one side of the face is common when the facial nerve is damaged. Facial paralysis on both sides of the face can be more difficult to recognize, but affected animals often drool and have a dull facial expression. In total facial paralysis, the animal cannot move its eyelids, ears, lips, or nostrils. In partial paralysis, the muscles of facial expression move less than normal.
The signs of facial paralysis vary with the location and severity of the injury. One or both sides of the face can be affected. Usually, the signs include loss of motor function, including the inability to blink, a drooping ear, a drooping upper lip, and drooling from the corner of the mouth. When the animal eats or drinks, food and water may fall out of the mouth. The nose may seem to turn away from the side of the injury because muscle tone on the injured side is reduced. Decreased tear production can cause one or both eyes to be dry.
Infection of the inner ear is a common cause of facial paralysis, especially in dogs with chronic skin conditions. This can be diagnosed with ear examination, x-rays, magnetic resonance imaging (MRI), computed tomography (CT) scans, and bacterial cultures. The prognosis for recovery can be good if the diagnosis is made early and the animal receives appropriate antibiotic treatment. However, the facial nerve paralysis can be permanent, and longterm administration of eye drops may be necessary.
A low-functioning thyroid gland (hypothyroidism) can also cause facial nerve paralysis. In such cases, thyroid replacement therapy can sometimes resolve facial paralysis completely.
Idiopathic facial paralysis (like Bell’s palsy in humans) is diagnosed in the absence of infection, reduced thyroid function, injury, or trauma. There is no treatment, and regular administration of lubricating eye drops may be necessary. One or both sides of the face can be affected, and the condition can be either temporary or permanent. It can occur on one side, disappear, and then occur on the other side at a later time. Permanent paralysis may give the face an unusual appearance but does not usually affect the quality of life in dogs.
Tumors that affect the facial nerve or middle ear can cause facial paralysis. Examining the middle ear with an otoscope (an instrument that allows a veterinarian to see into the ear), analyzing tissue samples, and using advanced imaging (MRI or CT) allow diagnosis. Depending on the type of tumor, animals can do well if they are treated early.
Electromyography, including electrical stimulation of the facial nerve, may be helpful to determine the severity of the injury. There is no specific therapy for injury except electroacupuncture, massage, heat applied to the affected muscles, laser therapy, and low level light therapy. Some animals may also need special water containers and soft food. The facial nerve can slowly regenerate, so repeated neurologic examinations can help determine if an animal is recovering. If there has been no improvement after 6 months, the chance of recovery is poor.