When I meet people at some kind of social gathering and they know I’m a veterinarian, they often ask questions like “What is the weirdest thing you’ve seen?” Sometimes they mean weird species of animals, sometimes they are looking for crazy gross stories, but my mind always goes a little more medical than that. I usually start thinking about the weirdest cases. They are looking for geckos, flying squirrels, 1.5kg tumours and limb amputations. I start thinking about the head trauma cats that go from comatose to miraculously almost normal, the lump the best pathologist I know couldn’t identify, and the dogs that couldn’t open their mouth more than an inch.
At a social gathering, I tell them about the weird species I see, and the cool gross surgeries. But here on my blog, I’m going to use the cases I find most interesting as topics. If you want the flashy stories, come visit St John’s and I’ll tell you over a pint down at the Duke.
SO! Today’s topic? LOCKJAW! WOOHOO! In 3 years I have had 2 cases with dogs that could not open their mouth more than an inch. One was a second opinion that went on to the Atlantic Veterinary College for all kinds of work up. He had essentially an autoimmune disorder affecting his masticatory muscles (the muscles that move your jaw), and his tongue and esophagus. Was super bizarre. He is being fed primarily through a tube that is implanted directly into his stomach while his esophagus recovers, and he can open his mouth more now. He’s had a rough time of it this year, but he is doing better. The second was one I received an emergency call about one morning, but ultimately saw a colleague of mine. His owners have not been able to pursue advanced diagnostics, so we are as of yet unsure of the cause for his inability to open his mouth properly, but it is just his jaw that is affected and he can eat on his own and is doing well despite being unable to open his mouth more than an inch.
So what causes a dog to be unable to open his mouth? Lockjaw, or trismus, can be caused by a number of things:
- Masticatory Muscle Myositis
This is a bit of a poorly understood disorder, but it basically the immune system attacking the muscles of mastication (otherwise known as chewing muscles!)
Inflammation of muscles, simply put. Can be immune mediated, can be caused by infection, can be for reasons never determined.
- Retrobulbar Abscess
This is an infection behind the eyeball. Causes all kinds of problem.
- Foreign Body
Dogs are silly. Sometimes they try to eat things they shouldn’t. Sometimes things get stuck in the guts, but sometimes things get stuck right in the mouth and interfere with jaw function.
- TMJ Disease
The temporomandibular joint (TMJ) is the hinge joint on your jaw. So, understandably, anything goes wrong with this and it causes jaw function issues.
- Craniomandibular Osteopathy
This is a disease of the bones in the head, and it can interfere with the TMJ, and as already mentioned this can be problematic for jaws.
The disease people think of when they hear “lockjaw”. Tetanus is caused by a toxin released by a bacteria. Dogs, compared to humans, have a natural resistance to tetanus toxin, so this is fairly uncommon and not nearly as much of a concern in dogs as it is in people.
- Muscular Dystrophy
Muscles control the jaw. So all I’m going to say, is muscle problems may manifest as jaw moving problems.
Now, I did not provide you with this list so you can diagnose your dog yourself. Do not do that. But if you are noticing that your dog is eating his food differently, or drinking funny, or barking weird, or basically anything that involves moving his jaw – pay attention! Maybe he can’t open his mouth! Time to make an appointment to see your vet. If on physical exam it is determined that there is indeed an issue with jaw movement, expect to be recommended blood work, sedation, and radiographs. This will help take the above list and narrow it down to a diagnosis so you can move forward with treatment and your dog can move his jaw again. Yay! Happy ending!