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Masticatory Muscle Myositis in Dogs

golden retriever chewing on red toy


MMM is an autoimmune disorder in which antibodies attack the 2M fibers in the masticatory (chewing) muscle group. A blood test was developed in 2004 at the University of California San Diego to confirm the circulating antibodies that attack 2M fibers. Masticatory Muscle Myositis (MMM) can occur in any dog but is more common in large breeds such as Golden RetrieversLabrador RetrieversDoberman Pinschers and German Shepherds.

Cavalier King Charles Spaniels may also be severely affected and believed to be genetically predisposed to developing MMM. If you recognize any of these signs of masticatory muscle myositis (MMM) you should promptly seek veterinary care.

  • Inability to open the jaw
  • Difficulty eating and drinking
  • Reluctance to play with toys
  • Sunken or protruding eyes
  • Pain in the jaw area
  • Swelling or atrophy of the jaw muscles

2M Antibody Blood Test

Early diagnosis of MMM is critical for successful treatment. The sooner a dog is properly diagnosed and begins treatment, the greater the chance of recovery.


The standard course of treatment consists of heavy, lengthy doses of corticosteroids such as prednisone. For dogs not able to tolerate the side effects of corticosteroids, azathioprine may be prescribed. Other drugs which have been considered for treatment of MMM include dexamethasone and cyclosporine. Your veterinarian will administer the right protocol based on your dog’s breed, age, health and the severity of MMM.

Cost to Treat: $50 to $100 per month

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