Facial paralysis in horses may result from injuries caused by rough handling, halters worn during anesthesia, facial surgery or skull fracture. 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 and a collapsed nostril. 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, drooling from the corner of the mouth, and absence of nostril flaring. When the animal eats or drinks, food and water may fall out of the mouth. The muzzle may seem to turn away from the side of the injury because muscle tone on the injured side is reduced.
Electromyography, including electrical stimulation of the facial nerve, can be used to determine the location and severity of the injury. There is no specific therapy for the injury except electroacupuncture, massage, and heat applied to the affected muscles. Some animals may also need special water containers and soft food. The facial nerve can regenerate over time, 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.
Infection of the inner ear and guttural pouch, arthritis of the joint between the hyoid bones and the skull, and equine protozoal myeloencephalitis are additional causes of facial paralysis. The outlook for recovery can be good if the diagnosis is made early and the animal receives appropriate antibiotic and anti-inflammatory treatment. Surgery to remove part of the hyoid apparatus may be helpful. However, the facial nerve paralysis can be permanent, and longterm administration of eye drops may be necessary.
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