Canine Masticatory Myositis Symptoms

Written by bryan cohen
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Canine Masticatory Myositis Symptoms
Dogs and Masticatory Myositis (dog image by Andrii IURLOV from

Masticatory Muscle Myositis (MMM) is an inflammatory muscle condition found in dogs and some other animals. This autoimmune disease causes antibodies circulating in the dog's blood stream to target the muscles of the lower jaw. This condition can be acute, manifesting in several attacks, or chronic, which may include attacks over the course of a long period of time. Several symptoms accompany the condition, but since they are not always obvious, it is important to take your dog to a veterinarian if you even suspect a symptom might be manifesting.

Swollen Jaw

The masticatory in MMM refers to the muscles used for chewing. Since the condition targets a special protein located only in the dog's lower jaw, this causes jaw swelling in acute cases. You may notice that your dog's jaw does not open nearly as wide as it typically does. The movement of the jaw will be limited, and having the jaw forcibly opened to normal width may cause the dog extreme pain. This symptom is most obvious when the dog is eating.

Swelling Complications

If you do not notice the swelling of the jaw, there are several consequences of a swollen jaw that may clue you in to MMM. Due to the difficulty in eating brought on by the jaw problem, the dog may have increased drooling. This swelling of the jaw may also make the dog's eyes seem to bug out in a process called exophthalmos. The dog will not enjoy having his head moved around in any way, and other areas like the tonsils, lymph nodes, and the neck may become swollen, as well. A fever may occur.


In more chronic cases, after the jaw has been worn down by MMM, you may notice that the dog's muscles have atrophied. The dog may appear to have a sunken head, especially at the top. Muscles around the jaw may shrink, and scar tissue may take their place. The head of the dog may begin to look like a skull, and the eyes may appear sunken because of the loss of muscle mass behind them.

Other Symptoms

A drawn-out spasm of the jaw may occur during MMM, but since there are other canine conditions that involve jaw spasms, it is difficult to make a judgment on this symptom alone. Eye issues may occur in relation to MMM, such as temporary blindness and conjunctivitis. These eye problems result from swelling compressing the optic nerves. As there is a lot of pain from the condition, you may notice whimpering during eating.

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