Dogs

Masticatory Muscle Myositis

Masticatory muscle myositis (MMM) is an inflammatory disease in dogs affecting the muscles of the jaw. It is also known as atrophic myositis or eosinophilic myositis. The disease mainly affects large breed dogs. There is a similar disease of the eye muscles found in Golden Retrievers. Symptoms of acute MMM include swelling of the jaw muscles and pain on opening the mouth. In chronic MMM there is atrophy of the jaw muscles, and scarring may result in inability to open the mouth (trismus). The disease is usually bilateral.

MMM is caused by the presence of 2M fibers in the muscles of the jaw. 2M fibers are not found elsewhere in the body, but they are close in structure to proteins found on the surface of bacteria. The immune system recognizes these proteins as foreign to the body and attacks them, resulting in inflammation. Diagnosis of MMM is through biopsy. Treatment is usually with corticosteroids, and in the case of trismus, manual opening of the mouth under anesthesia. Feeding very soft or liquid food during this time is usually necessary. Recurrence of MMM is common.

References

• Chrisman, Cheryl; Clemmons, Roger; Mariani, Christopher; Platt, Simon (2003). Neurology for the Small Animal Practitioner(1st ed.). Teton New Media. ISBN 1-893441-82-2
• Ettinger, Stephen J.;Feldman, Edward C.(1995).Textbook of Veterinary Internal Medicine(4th ed.). W.B. Saunders Company. ISBN 0-7216-6795-3

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