My pet seems fine, but her/his facial expression is not the same as it was yesterday. There is drool coming from the side of the mouth, and my pet appears unable to blink on the same side. A fleshy membrane will flick across the eye if I attempt to touch my pet’s face.
Rest assured, this is a common problem facing small animal companion animals. Cranial, or head, nerve disorders can involve any of the nerves of the head and face. The facial nerves are the most frequent nerves to be affected. Dysfunction of the facial nerve(s) can present as the sudden inability to blink or move the lips and ear on the side of nerve failure (facial nerve dysfunction). This may affect one or both sides of the face, at the same time or separated by hours or months.
The sudden failure of the facial nerve function results in loss of muscle tone, motor function and maintenance of muscle mass of the innervated muscle fibers receiving nerve supply. In this case, the muscles of facial expression become non-functional. Your pet’s lip(s) may droop, the ear(s) may remain upward or drooped without movement, and you may notice the third eyelid move across the eye if you move you hand toward the face. This latter movement is a protective mechanism and demonstrates that vision is intact, but your pet cannot blink the eye closed for protection of the eye. With time, contracture (shortening of the muscle fibers) will cause the denervated (muscles lacking nerve supply) muscle fibers to pull back, or contract, making the drooping lips look more normal.
In most cases, facial nerve dysfunction is a benign, non-progressive neuropathy, or nerve dysfunction. This is a preprogrammed, likely genetic, failure of nerve function. Changes are sudden in onset and often permanent.
Identifying other underlying causes, such as hypothyroidism (low thyroid function), which can be reversed, is the goal. It is important to have your veterinarian assess your pet as soon as possible after you notice any signs of facial change. Your veterinarian may recommended that a board certified veterinary neurologist examine your pet to ensure the noted nerve dysfunction does not represent a more serious condition.