Masticatory Muscle Myositis (MMM)

What is MMM?

Masticatory Muscle Myositis is an autoimmune disease, and the muscles in the dog’s lower jaw are involved.  The masticatory in Masticatory Muscle Myositis refers to the muscles used for chewing.   The dog’s jaw swells and becomes sore and tender to the touch. You may also notice that your dog’s jaw does not open as wide as it usually does.  His jaw  movement is limited, and  forcibly opening his mouth will cause him severe pain.


The easiest way to spot this problem is to watch him while he’s eating.  He may have trouble chewing or even reaching down for his food.  He may refuse some of his favorites if they happen to be crunchy or chewy.  Until his jaw returns to normal, feed him softer and less chewy food.  Elevating his food dish may also help.

If you don’t notice his swollen jaw, here are some other symptoms that may give you a clue.

  • Increase in drooling from difficulty eating
  • Eyes seem to bulge.  The inner eyelid may partially close
  • Will not enjoy having his head moved around
  • Tonsils, lymph nodes, and the neck may become swollen
  • May be feverish or sluggish

Your dog may still be active and alert even though he cannot open his mouth normally.  Sometimes he can’t open it at all.


Your vet will treat Masticatory Muscle Myositis by prescribing a treatment such as prednisone.   However, there are side effects.  Prednisone will make your dog more thirsty, and he and will urinate more frequently. Your dog will also have an increased appetite.  During this period of increased appetite, he may gain unwanted weight. While his jaw is tender, keep him on a soft diet and avoid rawhides and other chew toys.  Green beans make an excellent soft supplement to his regular meal.  As the jaw returns to normal, you can add baby carrots and rice cakes to his diet.  Baby carrots are an excellent snack because: 1) they taste good and dogs generally love them and 2) this snack will let you monitor his jaw.  If he is able to chew them up easily, his jaw is improving.

No Preventative Measures

Unfortunately there are no preventative measures to reduce risk of Masticatory Muscle Myositis at this time.  If your dog is diagnosed with MMM, stay in close contact with your vet so that he can monitor your dog’s progress and adjust his medication.  Your vet will gradually wean him from the medication over time and as his condition improves.

photo credit: dogbrush

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