Masticatory Myositis in Dogs

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Masticatory myositis is a condition that causes pain when a dog opens his mouth or chews.

What Is Masticatory Myositis?

The masticatory muscles are those that have a part in chewing. They are over the cheek and temple areas.

Myositis means muscle inflammation. So, in masticatory myositis, there is inflammation that negatively affects the ability of the masticatory muscles to work. It causes trismus, which is the inability to open the mouth.

Masticatory myositis is an immune-mediated condition during which the body attacks its 2M muscle fibers, which are the ones used for chewing. Scientists don't yet know what causes a dog's body to attack those tissues.

Signs of Masticatory Myositis in Dogs

Dogs with masticatory myositis are usually around three years of age. The condition is most common in the following dog breeds:

• Labrador and golden retrievers
• German shepherds
• Dobermans
• Cavalier King Charles spaniels

Initially, the dog's face may appear swollen. The dog may run a fever and experience swollen lymph nodes. He's likely to lie around and act lethargic.

As time goes on, the masticatory muscles begin to atrophy, or shrink. They become tight, and the jaws are increasingly unable to open. Eating is difficult, and food may drop out of the mouth if the dog tries to eat at all.

Diagnosis of Masticatory Myositis in Dogs

Many other conditions can cause pain in a dog's face, difficulty chewing, and dropped food, including:

• A foreign object stuck in the mouth or throat
• Tetanus
• Tooth root abscess
• Dislocated jaw
• Polymyositis (inflammation of muscles generally in the body, not just chewing muscles)
• Jaw cancer

Therefore, a veterinarian will need to do some testing to determine what's going on. That may require anesthesia to examine the oral cavity thoroughly, x-rays, and biopsy of the affected muscles.

A particular blood test can find antibodies to the 2M muscle fibers, but there can be false negatives, especially in the early stages of the condition.

Treatment of Masticatory Myositis in Dogs

Treatment of this condition requires suppressing the dog's immune system. Usually, high doses of corticosteroids accomplish that. Once the jaw is moving normally again, the medication may be gently tapered off over months. Many dogs need to be on medication for life, and in that case, the lowest possible dose that keeps the signs at bay is required.

Certain chemotherapy drugs that lower the immune system may also be chosen to help the dog. Some veterinarians use corticosteroid and cyclosporine, which is an immune-modulating drug that can sometimes lower the requirement for corticosteroids.

In the early stages of treatment, the dog may need to be fed gruel (semi-liquid) with a syringe. The risk of aspiration pneumonia is present during that time, and the owner should watch for coughing and wheezing.

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