Masticatory Muscle Myositis in Dogs

Masticatory Muscle Myositis, or MMM, is a condition in which the muscles of your dog's jaw become inflamed. It occurs due to an autoimmune response, in which your dog's own immune system attacks the muscle fibers of his jaw. It's more common in some breeds of dog than in others and can be acute or chronic. Read on to learn more about Masticatory Muscle Mysotitis in dogs.

Risk Factors for Masticatory Muscle Myositis in Dogs

MMM occurs most often in Retrievers, German Shepherds and Doberman Pinschers. Young and middle-aged dogs develop this disease more often than other dogs. This type of myositis may be acute, meaning that symptoms come on suddenly, or chronic, meaning that symptoms develop gradually and get worse over time. Masticatory Muscle Myositis can make chewing painful for your dog, or inhibit his ability to open his mouth altogether.

Symptoms of Masticatory Muscle Myositis in Dogs

If your dog develops masticatory muscle myositis, he may experience swelling of the muscles in the forehead or face. He seem reluctant to chew food, since opening the mouth and chewing can be painful for dogs with this condition. In acute cases of this disease, your dog may seem suddenly unable to open his mouth at all. In chronic cases, your dog's pain may gradually become so severe that he cannot open his mouth.

MMM can cause your dog's eyes to bulge, and can lead to prolapse of the inner eyelid (a condition in which your dog's inner eyelid slips out of place and becomes visible at the corners of his eyes). Your dog may drool excessively and develop a fever. Over time, the muscles of your dog's jaw can shrink, giving him a thin-faced, hollow-cheeked appearance. This is most common in the later stages of chronic Masticatory Muscle Myositis.

Diagnosing and Treating Masticatory Muscle Myositis in Dogs

There are a number of other conditions that can cause symptoms similar to those of MMM. Tetanus, abscesses, polymyositis (a similar condition that affects all the muscles of the body), jaw dislocation, muscular dystrophy and abnormal bone growth could all cause these symptoms. Acute pain upon opening the mouth, or a sudden inability to open the mouth, is often due to the presence of a foreign object lodged inside the mouth. 

Your vet will need to rule out these other possible causes of your dog's symptoms before he can diagnose Masticatory Muscle Myositis. A complete physical exam and medical history can help. Blood tests, X-rays, CT scans and electromyography (EMG) can help your vet confirm the presence of Masticatory Muscle Myositis.

Immunosuppressive drugs and corticosteroids are usually administered to manage this condition. MMM causes inflammation of the muscles and can cause scar tissue to form in the muscles, hampering their function. The sooner your dog is diagnosed, the better his prognosis will be. Dogs who can no longer open their mouths will need to be tube-fed. 

Monitor your dog's progress carefully from the time his treatment begins. Some dogs may need to remain in treatment for the rest of their lives. If your dog is not being tube-fed, switch him to soft food instead. Avoid giving him chew toys or chewy treats, like rawhide.