If your normally food-loving dog suddenly develops difficulty eating or drinking, or opening his mouth appears painful, he might be suffering from canine masticatory myositis. This neuromuscular problem affects the muscles in his jaw, causing swelling and making it hard for him to chew, or even open his mouth to bark. If your dog experiences these symptoms, take him to the vet at once for diagnosis and treatment.
While myositis seems to occur overnight in many dogs, in others it's a gradual process. The acute, or sudden, form is less common than the chronic version. The muscles on the top of the dog's head might swell initially, followed by muscle wasting in the jaw muscles. These atrophied muscles are replaced by scar tissue. As the scar tissue develops, the top of head and cheeks start sinking in. Because of inflamed muscles, the eyes might start bulging out.
Commonly Affected Breeds
While any dog can suffer from myositis, the condition is more prevalent in certain breeds. According to the California-based Mar Vista Animal Medical Center, the most commonly affected breeds include the golden and Labrador retrievers, German shepherd, Doberman pinscher and Cavalier King Charles spaniel. Both sexes are equally represented in canine patients with the disorder.
What brings on masticatory myositis isn't clear, but it might be an immune-related disorder. In some cases, it results from an infectious agent. In certain dogs, the myositis might be a pre-cancerous change, or cancer elsewhere in the body might cause an immune reaction in the masticatory muscles, according to Davies Veterinary Specialists.
Your vet must examine your dog physically and rule out other, obvious causes of mouth issues, such as a foreign body stuck inside it or tumors. This requires anesthesia for a thorough going-over. In severely affected dogs, the vet might not be able to open the jaws even when the dog is anesthetized. Your vet also takes blood samples to conduct the 2M antibody test, a special test for masticatory myositis.
Your vet might prescribe steroid medication to suppress your dog's immune system. It's not a short treatment course -- your dog might take this drugs for six months or more, although the dosage is adjusted regularly by your vet. While dogs treated promptly after their symptoms appear usually recover, those with a great deal of fibrous scar development might not do well.
By Jane Meggitt
Michigan Veterinary Specialists: Masticatory Myositis
Davies Veterinary Specialists: Myositis
Mar Vista Animal Medical Center: Masticatory Myositis
Cavalier Health: Masticatory Muscle Myositis in the Cavalier King Charles Spaniel
About the Author
Jane Meggitt has been a writer for more than 20 years. In addition to reporting for a major newspaper chain, she has been published in "Horse News," "Suburban Classic," "Hoof Beats," "Equine Journal" and other publications. She has a Bachelor of Arts in English from New York University and an Associate of Arts from the American Academy of Dramatics Arts, New York City.