If your dog's face is drooping on one side, you are right to be concerned. Among humans, a droopy mouth or face is often indicative of a stroke and strokes need immediate medical attention. Interestingly though, among dogs, strokes are not as common as it happens in humans. While years ago, it was thought that dogs could not get strokes because of having a more extensive blood supply to the brain compared to humans, nowadays that thinking has changed. While dogs can and do have strokes, there are however several other more common medical conditions that may cause a dog's face to droop on one side. Following are a few potential causes.
Facial Nerve Paralysis
A dog's face is innervated by a variety of nerves. In particular, the facial nerves, also known as cranial nerves, basically, nerves that stem from the dog's skull (cranium), are responsible for a variety of functions, including controlling the muscles of a dog's face. Cranial nerve VII is known for innervating a great part of the dog's face with ramifications branching out to serve different facial areas.
In a normal, healthy dogs with a well-functioning nervous system, the cranial nerves that control movement of the muscle of a dog's ears, nose and lips allow the dog to move such facial muscles as needed. In a dog suffering from neurological issues, instead, control of these muscles is difficult or not possible.
In particular, damage to the buccal branch of the facial nerve can affect control of the muscles of the dog's lips causing a dog's mouth to droop to one side; whereas, damage to the dog's palpebral branch of the facial nerve can affect control of the muscles of the dog's eyelids, causing drooping of the upper eyelids (ptosis).
Because the muscles are unable to keep those facial muscles tight, they appear to be therefore drooping causing droopy ears, drooling out saliva from the mouth (think about how it feels when you're mouth is numb when undergoing dental work) and an inability to blink on the affected side.
Paralysis is the medical term used to depict the loss of muscle control of a part or several parts of the dog's body. Paralysis of the facial nerve in dogs can be due to a variety of causes which interfere with or prevent the nerves innervating the muscles of the face from functioning properly.
A Traumatic Injury
One of the most common causes of loss of muscle function is a traumatic event that has caused the cranial nerve to lose communication, therefore causing the dog's face to droop to one side. Trauma may cause the nerve to be severed partially or completely, crushed, compressed, or stretched.
What kind of traumatic incidents can cause a dog's face to droop to one side? A car accident, rough handling, or perhaps a complication from some type of surgery such as bulla osteotomy or total ear ablation, can lead to disruptions of the communication between nerves and muscles.
An Ear Problem
Sometimes, a dog's ear can get infected with the end result of causing so much swelling and inflammation that it affects the facial nerves. This can be seen in severe cases of middle ear infections or inner ear infections. The cranial nerve VII is known for running in close proximity to the dog's middle ear. Affected dogs often show signs of ear problems such as shaking the head side-to-side, tilting the head and scratching the ears.
Dog Endocrine Problems
Endocrine problems are simply conditions that affect the dog's endocrine system which is a collection of glands that secrete hormones. Hypothyroidism, a condition where the dog's thyroid produces too little hormones, can be a cause for the drooping of the dog's face. Another potential cause is Cushing's disease, which occurs when the dog's body is exposed to excessive levels of cortisol.
There is always the chance for cancer being a culprit for a dog's facial paralysis. In this case, some mass or growth may be putting pressure on the facial nerves, causing them to no longer function as they should. What types of cancer can cause this? According to veterinarian Dr. Christian a tumor in the dog's chest, neck or inner ear can cause a dog's face to be drooping on one side and not always when this happens will there be other symptoms. It's always best to see the vet if you notice drooping of your dog's face so to rule out any potential types of cancers, especially in older dogs who are more predisposed to them.
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Idiopathic Facial Nerve Paralysis
Sometimes, an exact cause for the drooping of the dog's face cannot be found. When vets cannot find an underlying cause, they refer to the condition as being "idiopathic" which simply means of unknown cause.
As frustrating as it can feel not knowing the underlying cause, it's important to recognize that this is a diagnoses of exclusion, meaning that before coming to this conclusion, your vet will have tested for other possible disorders first. Your vet should have therefore have excluded any potential ear infections, thyroid problems and your dog has no history of trauma.
Because no cause is identified, there is no treatment but only supportive care such as use of artificial tears, if the affected drooping eye is not producing sufficient tears. The condition may have different outcomes. In some cases it may resolve spontaneously, while in others is may be permanent. Dogs may get better, and then only later the other side is affected. Fortunately, while facial paralysis may be unsightly for dog owners, the dog's quality of life is not typically affected.
"Causes of facial nerve dysfunction in dogs and cats included surgical and nonsurgical trauma, neoplasia, and otitis media/interna. Facial neuropathy was judged to be idiopathic in 74.7% of dogs and 25% of cats."~J Am Vet Med Assoc. 1987.
At the Vet's Office
Your vet will conduct a throughout physical examination with a particular emphasis on a neurological exam. Your vet may touch the outside corner of the eye on the side of the affected face so to check if your dog has retained an ability to blink.
Other tests may include a complete blood count, chemistry profile and thyroid panel, preferably a Michigan State University complete thyroid panel.
If your dog has a history of trauma, your vet may suggest an electromyography (EMG), which consists of placing a needle electrode in a muscle to detect electrical activity. This procedure is done under anesthesia but signs of facial paralysis might not be evident until several days later following the onset of symptoms.
A thorough ear exam is necessary to rule out problems with the dog's ear. Because the inner ear cannot be visualized well with an otoscope the vet may require an MRI to identify this possibility.
Also, the vet may recommend a Schirmer tear test considering that the dog's facial nerves are also responsible for producing tear. If tear production is affected, the vet may suggest lubrication of the affected eye with artificial tears to prevent it from drying out and sustaining damage such as the formation of ulcers on the dog's cornea.
Treatment for a dog's face drooping on one side depends on the underlying cause. For example, if there is an ear infection, it will be treated with a course of antibiotics. Once the underlying cause (if identified) is addressed, the symptoms should subside shortly thereafter; however, if there's no improvement following 6 months, the chances for recovery are generally poor.
"Therapy for injury may include massage and heat of denervated muscles for 15 min, 2−3 times/day, to maintain their integrity while awaiting any nerve regeneration. The facial nerve can regenerate ~1–4 mm/day, so serial neurologic examinations can also help determine the prognosis. If there has been no improvement after 6 mo, the chance of recovery is poor." ~Merck Veterinary Manual
- DVM360: Cranial nerve disorders (Proceedings)
- DVM360: Cranial nerve disorders of dogs and cats (Proceedings)
- Merck Veterinary Manual: Overview of Facial Paralysis
- DVM360: Brain infarction in canine patients