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Health & Wellness

Lockjaw in dogs and cats: what is trismus?

Although rare, some dog and cat injuries can cause tetanus, which can lead to trismus. Here’s how to spot the symptoms.

If you notice your pet is having difficulties chewing or even opening their mouth, they may be suffering from trismus. This condition causes clenching of the teeth and spasms of the muscles used for chewing, making it difficult for a dog or cat to open their mouth – hence trimus’s popular nickname: lockjaw. 

What is lockjaw?

Lockjaw, or trismus, occurs when jaw muscles clench, making it difficult for your pet to open their mouth. It’s generally a symptom of tetanus, an infection that can be contracted through open wounds – so it’s important to have your pet treated by a vet if they’ve recently been injured. 

Thankfully, dogs and cats have a natural resistance to tetanus, so it’s relatively rare that they contract it. But it’s important to contact your vet right away if your pet is showing signs of trismus, especially if they recently suffered an injury. If symptoms do occur, they typically show up about 5 to 10 days after an injury.

What causes lockjaw in dogs and cats

“The most common reason, which is very rare in cats and dogs, is a bacterial infection,” Dr. Kelly Diehl, DVM, MS, Dipl. ACVIM (SAIM), a former vet and the senior scientific programs and communications adviser at Morris Animal Foundation, says. “These bacteria produce a toxin that causes tetanus. Cats are also more resistant to the effects of this toxin than dogs.”

Another more common cause of trismus is a condition called masticatory myositis, which is inflammation of the chewing muscles. Inflammation is caused by an immune-mediated attack of the muscles, leading to trismus and the wasting away of the muscles at the top of the affected animal’s head.

Polymyositis is another very rare, but potential, cause of trismus in cats and dogs. The muscle inflammatory disease occurs for many reasons — sometimes it’s infectious and other times it’s triggered by abnormal activity of the immune cells. Whatever the cause, if inflammation affects the muscles your pet uses for chewing, you can bet trismus can result.

Of course, trismus can also be caused by trauma or other problems in the temporomandibular joint (TMJ), which is the hinge joint where your pet’s upper and lower jaw meets. Fractures, dislocation and even arthritis can affect how a dog or cat opens their mouth.

One hereditary condition we see in West Highland White Terriers (Westies) and other breeds is called craniomandibular osteopathy, a non-cancerous, non-inflammatory disease that generally occurs due to irregular bone growth. When bony changes affect the TMJ, trismus can certainly be the result.

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The symptoms of trismus

The most obvious trismus symptom dogs and cats experience is the inability to open their mouth. Even if your pet’s jaw isn’t necessarily “locked,” you may notice excessive drooling or even eye issues, including a more visible third eyelid, eye discharge, conjunctivitis and their eyes rolling in and out of the eyelids because of muscle loss around the head and jaw. 

“Contraction of the lip muscles, bulging eyes and very erect ears can also be seen, all due to muscle spasming,” Dr. Diehl says. “Animals with tetanus are very sensitive to touch and sound, too. Eventually, the toxin can paralyze other muscles, including those involved with breathing, leading to death.”

While there are many causes of lockjaw in pets, thankfully, they’re all relatively rare. Still, if you notice your pet having trouble picking up food or chewing, or, in chronic cases, if the top of your pet’s head looks caved in and their skull bones are much more visible, trismus may be the reason, and you should contact your vet immediately.

How to treat trismus

If available, a vet may give your dog or cat an antitoxin infusion to kill the bacteria causing tetanus. Sedatives and muscle relaxants can also be used as supportive care in patients. Your vet will care for any wounds your dog or cat may have sustained, too.

“Antibiotic therapy directed at tetanus causing bacteria is a cornerstone of therapy but supportive care with fluids might be needed in some cases until a pet is able to eat and drink normally,” Dr. Diehl says. 

There’s no specific prevention for tetanus other than making sure that any wounds your pet endures are treated by a veterinarian right away. If your pet has recently sustained any type of wound injury and is exhibiting signs of trismus, it’s important you seek veterinary care immediately.

The Dig, Fetch Pet Insurance's expert-backed editorial, answers all of the questions you forget to ask your vet or are too embarrassed to ask at the dog park. We help make sure you and your best friend have more good days, but we’re there on bad days, too.

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