Logan Steele
Masticatory Muscle Myositis (MMM) is an autoimmune disease that affects dogs, causing inflammation and pain in the muscles required for chewing. While the exact cause of MMM is unknown, it is believed to have a strong genetic component, with certain breeds like German Shepherds, Retrievers, and Doberman Pinschers being more prone to the disease. Environmental factors, such as exposure to allergens, toxins, and infections, are also thought to play a role in triggering MMM. The disease can cause severe pain and difficulty in eating, chewing, and even opening the mouth, requiring aggressive treatment with steroids and immunosuppressants.
| Characteristics | Values |
|---|---|
| Definition | An immune system disorder where the dog's immune system identifies the dog's own muscle tissue as foreign and attacks it |
| Type of disease | Autoimmune disease |
| Affected muscles | Masticatory muscles (chewing muscles) |
| Affected breeds | German Shepherds, Retrievers, Cavalier King Charles Spaniels, and Doberman Pinschers |
| Age of onset | Average age of 3 years, but cases as young as 4 months |
| Symptoms | Muscle inflammation, muscle atrophy, pain, malnutrition, difficulty drinking, aspiration pneumonia, fibrosis, trismus, and stress |
| Diagnosis | Blood test (2M antibody ELISA assay), muscle biopsy, diagnostic imaging |
| Treatment | Steroids, immunosuppressants (e.g. prednisone, dexamethasone), soft or liquid food |
| Prognosis | Early diagnosis and treatment lead to a good prognosis; end-stage may require surgery or gastric feeding tube |
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What You'll Learn
Masticatory muscle myositis (MMM) is an autoimmune disease
The disease causes extreme pain and inflammation in the affected muscles, making it difficult for dogs to open their mouths to eat, chew, or play. The acute phase of MMM may go unnoticed or be confused with other conditions affecting the head, eye, teeth, mouth, or jaw due to its vague symptoms. However, as the disease progresses, muscle shrinkage and wasting occur, and the bones of the head become more prominent.
MMM is characterised by inflammation, necrosis, and atrophy of the masticatory muscles. The immune system attacks the Type 2M muscle fibres, which are unique to the temporalis and masseter muscles of the head and jaw. Diagnosis of MMM can be made through a blood test that detects autoantibodies to these 2M fibres or through a muscle biopsy, which helps determine the progression of the disease and subsequent prognosis.
The treatment for MMM typically involves the use of immunosuppressive drugs, such as corticosteroids like prednisone, to counteract the over-excitation of the immune system. Early and aggressive treatment offers the highest chance for remission. While most dogs respond well to treatment, MMM can be a recurrent condition and may become more difficult to treat with each relapse. Successful feeding methods during treatment may include softening dry food with warm water or providing canned food or liquid formulations.
The outlook for dogs with MMM depends on the degree of inflammation and the response to therapy. Early diagnosis and immediate treatment can lead to a full recovery of jaw function and muscle mass. However, in some cases, scar tissue formation within the masticatory muscles can cause permanent problems. Additionally, long-term use of certain medications, such as prednisone, can lead to muscle atrophy and other side effects, including excessive appetite, thirst, and increased urination.
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MMM affects the muscles of the head and jaw
Masticatory Muscle Myositis (MMM), or eosinophilic myositis, is an autoimmune disease that affects the muscles of the head and jaw required for chewing. Myositis refers to muscle inflammation or swelling. This disease attacks the special fibres found only in the muscles of the head and jaw, causing extreme pain and preventing dogs from opening their mouths to eat, chew or play.
MMM affects the Type 2M muscle fibres, which are unique to the temporalis and masseter muscles of the head and jaw. These fibres are not found elsewhere in the body, and the immune system identifies them as foreign, attacking them and causing inflammation. The inflammation caused by MMM can result in a degree of exophthalmos, or protrusion of the eyeball, due to the swelling of inflamed muscles in the head.
The disease has both acute and chronic forms, with dogs progressing from acute to chronic over time if untreated. The acute phase may go unnoticed or be confused with other conditions, as symptoms can be vague. During this phase, dogs may experience ocular abnormalities such as exophthalmos and conjunctival hyperemia, as well as vision loss due to optic nerve compression. The chronic form of MMM may include muscle shrinkage as the bones of the head become more prominent.
The ultimate degree of recovery of jaw function and muscle mass depends on the extent of damage to the muscle tissue. If MMM is diagnosed early and treatment is started promptly, dogs usually regain normal jaw function and the ability to open and close their mouths without pain. However, in some cases, scar tissue can form within the masticatory muscles, causing permanent problems.
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MMM is more common in large dog breeds
Masticatory Muscle Myositis (MMM) is an autoimmune disease where the body attacks the muscles of the head and jaw required for chewing. The disease causes the muscles to become swollen and painful, and dogs with MMM cannot open their mouths without excruciating pain. They cannot eat, chew, or play with toys. MMM can be recurrent and is more difficult to treat each time.
The cause of MMM is unknown, but it is believed to be triggered by environmental factors such as exposure to allergens, toxins, and infections. MMM can also be caused by adverse reactions to medications and vaccinations. The disease affects Type 2M muscle fibres, which are unique to the temporalis and masseter muscles of the head and jaw. These fibres are not found elsewhere in the body, and the immune system recognises them as foreign, attacking them and causing inflammation.
Diagnosis of MMM is typically done through a biopsy of the temporalis or masseter muscles or a 2M antibody assay blood test. Treatment for MMM usually involves high doses of steroids (prednisolone) or other immunosuppressive drugs to counteract the 'over-excitation' of the immune system. Early aggressive treatment offers the highest chance for remission, and successful feeding may require softening dry food with warm water or canned food.
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The disease causes muscle inflammation and prevents jaw movement
Masticatory muscle myositis (MMM) is an autoimmune disease that affects dogs. It causes inflammation and swelling of the masticatory muscles, which are the muscles involved in chewing. The disease gets its name from the fact that it affects the Type 2M muscle fibres, which are unique to the temporalis and masseter muscles of the head and jaw.
As a result of the inflammation and swelling, dogs with MMM experience excruciating pain when opening their mouths, making it difficult for them to eat, chew, or even play with toys. The swelling restricts jaw movement and can lead to muscle atrophy, or muscle wasting, if left untreated. In some cases, scar tissue can form within the masticatory muscles, causing permanent problems with jaw movement.
The specific cause of MMM is unknown, but it is believed to be triggered by the dog's immune system mistakenly identifying the Type 2M muscle fibres as foreign and attacking them. This can be due to a variety of factors, including bacterial or viral infections, vaccinations, stress, exposure to allergens or environmental toxins, and reactions to medication. While any dog can develop MMM, some may be genetically predisposed to immune-mediated diseases, including MMM.
Diagnosis of MMM is typically done through a blood test that detects circulating autoantibodies to the 2M fibres, known as a 2M antibody ELISA assay. A muscle biopsy may also be performed to determine the level of inflammation and the severity of fibrosis, which is the formation of scar tissue. Early diagnosis and appropriate therapy are crucial for a good prognosis, as MMM can be a recurrent and progressively more difficult condition to treat if left untreated.
The recommended treatment for MMM is typically an immune-suppressive dose of corticosteroid medication, such as prednisone, given over several months. Feeding soft or liquid food may be necessary during this time. The degree of recovery of jaw function and muscle mass depends on the extent of damage to the muscle tissue.
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MMM can be treated with steroids and immunosuppressants
Masticatory muscle myositis (MMM) is an autoimmune disease that affects dogs. The body's immune system identifies the dog's own muscle tissue as foreign and attacks it, causing inflammation and pain. While the disease can be genetic, it can also be triggered by bacterial or viral infections, vaccinations, stress, exposure to allergens, reactions to medication, or exposure to environmental toxins.
Steroids are typically the treatment of choice for MMM. However, it is important to note that steroids can interfere with the 2M antibody test, decreasing the quantity of circulating antibodies in the blood and potentially resulting in a false negative. Therefore, it is ideal to perform a muscle biopsy or 2M antibody test before starting steroid treatment.
During the acute phase of MMM, corticosteroids help achieve aggressive immunosuppression. This immunosuppressive dosage should be continued until the dog has maximum jaw function and normal CK levels. Feeding very soft or liquid food during this time is usually necessary, as the dog may have difficulty eating due to jaw pain and swelling.
It is important to note that long-term prednisone therapy can have side effects, such as muscle atrophy, excessive appetite, excessive thirst, and increased urination. Additionally, successful feeding may require softening dry food with warm water or canned food or blending it into a gruel. There are also calorie-dense liquid formulations that may be prescribed by a veterinarian.
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Frequently asked questions
Masticatory muscle myositis (MMM) is an autoimmune disease where the body attacks the muscles of the head and jaw required for chewing. The disease affects Type 2M muscle fibres, which are unique to the temporalis and masseter muscles of the head and jaw.
The symptoms of MMM include muscle inflammation, muscle wasting, muscle atrophy, pain, malnutrition, difficulty drinking, aspiration pneumonia, fibrosis, trismus, and stress. Dogs with MMM are unable to open their mouths without excruciating pain, and have trouble eating, chewing, or picking up toys.
Masticatory muscle myositis has a genetic component and is more common in large breeds such as German Shepherds, Retrievers, Cavalier King Charles Spaniels, and Doberman Pinschers. However, it can occur in any breed and in both male and female dogs. The average age of MMM patients is 3 years, but there have been cases of dogs as young as 4 months old with the disease.
