Dominic Stone
Masticatory Muscle Myositis (MMM) is an autoimmune disease in dogs where the body attacks the muscles of the head and jaw required for chewing. The cause of the disease is unknown, but it is believed to be triggered by bacterial and/or viral infections, vaccinations, stress, exposure to allergens, reactions to medication, exposure to environmental toxins, or cancer. While trauma is not cited as a direct cause of MMM, it can lead to complications such as mandibular luxation (dislocation) or fracture, and increased inflammation in torn muscles.
| Characteristics | Values |
|---|---|
| Cause | Masticatory Muscle Myositis (MMM) is an autoimmune disease where the body attacks the muscles of the head and jaw. |
| Symptoms | Inability to open the mouth, swollen chewing muscles, excruciating face pain, muscle atrophy, and impaired vision. |
| Diagnosis | Blood test, muscle biopsy, neurological exam, oral exam, and imaging. |
| Treatment | Immunosuppressive drugs, steroids, and immunomodulators. |
| Prognosis | Fair, with early diagnosis and treatment. Relapses are common and may be more difficult to treat. |
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What You'll Learn
Masticatory muscle myositis (MMM) is an autoimmune disease
MMM can be caused by a variety of factors, including bacterial and viral infections, vaccinations, stress, exposure to allergens or environmental toxins, and reactions to medication. In some cases, it may be associated with cancer or parasitic infections. The exact cause of MMM is often unknown, and the disease can affect any breed, gender, or age of dog, although it typically occurs in young to middle-aged dogs.
The symptoms of MMM can include difficulty moving the jaw, swollen chewing muscles, excruciating facial pain, and sunken eyes as the muscles behind the eyes shrink. In some cases, there may be swelling around the eyes, leading to impaired vision. The acute phase of the disease may be difficult to detect, as symptoms can be vague and similar to other conditions affecting the head, eyes, teeth, mouth, and jaw. However, if left untreated, MMM can progress to the chronic phase, which includes muscle shrinkage and wasting.
MMM can be diagnosed through a blood test that measures the level of antibodies attacking the masticatory muscles, known as a 2M antibody test. A muscle biopsy may also be performed to determine the progression of the disease and subsequent prognosis. Treatment for MMM typically involves immunosuppressive medications such as high doses of steroids to counteract the immune system's activity against the muscles and return it to normal. Early and aggressive treatment is crucial to prevent severe muscle atrophy and dysfunction, which can lead to blindness, an inability to eat, and difficulty walking.
While the prognosis for dogs with MMM is usually fair, improvement may take several weeks, and the disease can be recurrent and more difficult to treat with each relapse. Corticosteroids, a common treatment for MMM, can cause muscle atrophy, giving the impression that the dog's condition is worsening. Therefore, it is essential to closely monitor the dog during treatment and slowly taper medications to prevent relapse.
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MMM causes the dog's immune system to attack its own muscle tissue
Masticatory muscle myositis (MMM) is an autoimmune disease in which the dog's immune system mistakenly identifies its own muscle tissue as foreign and attacks it. This disease specifically targets the masticatory or chewing muscles, which are involved in opening the mouth and chewing. The exact cause of MMM is unknown, but it is believed to be triggered by various environmental factors and certain predisposing factors.
The immune system normally protects the body from foreign invaders such as bacteria and viruses. However, in the case of MMM, the immune system becomes overactive and attacks the dog's own muscle tissue. This abnormal immune reaction leads to inflammation and damage to the masticatory muscles. The disease affects the Type 2M muscle fibers, which are unique to the temporalis and masseter muscles of the head and jaw.
The symptoms of MMM include severe muscle pain, muscle swelling, and an inability to open the mouth or chew. The pain is so intense that dogs often vocalize loudly if they attempt to open their mouths. As the disease progresses, muscle fibers waste away and are replaced by scar tissue, resulting in muscle atrophy and loss of muscle mass on the head. In some cases, the eyes may appear sunken as the muscles behind the eyes shrink, and there may be swelling and impaired vision.
MMM can occur in any breed and affects both male and female dogs, although it is more common in young to middle-aged dogs and certain large breeds such as German Shepherds, Labrador Retrievers, and Doberman Pinschers. While the exact cause of MMM is unknown, suspected triggers include bacterial and viral infections, vaccinations, stress, exposure to allergens and environmental toxins, and reactions to medications. Additionally, there may be a genetic predisposition, as some dogs are more susceptible to immune-mediated diseases.
The diagnosis of MMM is made through specialized blood tests that detect circulating autoantibodies attacking the muscle fibers, as well as muscle biopsies to determine the level of inflammation and tissue deterioration. Treatment typically involves long-term, tapering doses of corticosteroids to suppress the immune system's attack on the muscle fibers. Other immunosuppressive drugs, such as azathioprine and cyclosporine, may also be used in combination with steroids. Early diagnosis and treatment are crucial for a positive outcome, as MMM can be a recurrent and potentially life-threatening condition.
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MMM can be caused by bacterial infections
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 the Type 2M muscle fibres, which are unique to the temporalis and masseter muscles of the head and jaw. The symptoms of MMM include muscle shrinkage, a stiff gait, muscle pain, and an inability to open the mouth, eat, or chew.
While the exact cause of MMM is unknown, it is believed to be related to the exposure of the myofibrillary IIM protein by some unidentified process, such as prior inflammation, infection, or trauma. Bacterial infections are one of the suspected triggers of MMM, along with vaccinations, stress, exposure to allergens, reactions to medication, and exposure to environmental toxins.
MMM can be diagnosed through a blood test that measures the level of antibody directed against the masticatory muscle (2M antibody titre test) or a muscle biopsy, which is used to determine the level of inflammation and the severity of fibrosis. Treatment for MMM typically involves immunosuppressive doses of corticosteroids, such as prednisone, given over a period of months. Early aggressive treatment offers the highest chance for remission.
MMM can be a recurrent condition and may become more difficult to treat each time. The prognosis declines with subsequent episodes of the disease due to fibrous changes in the muscle. Successful feeding for dogs with MMM may require softening dry food with warm water or canned food or blending it into a gruel.
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MMM can be treated with immunosuppressive drugs
Masticatory Muscle Myositis (MMM) is an autoimmune disease that affects dogs. It causes the body to attack the muscles of the head and jaw required for chewing, making it extremely painful for dogs to open their mouths to eat, chew or play with toys. The disease affects Type 2M muscle fibres, which are unique to the temporalis and masseter muscles of the head and jaw. MMM can be treated with immunosuppressive drugs.
MMM can be diagnosed by a simple blood test that measures the level of antibody directed against the masticatory muscle (2M antibody titre test). Other tests may be necessary to rule out potential infections or the presence of cancer in the body. The treatment for MMM typically involves trying to counteract the 'over-excitation' of the immune system by giving drugs to suppress it. The main treatment is usually high doses of steroids (prednisolone).
Other immunosuppressive drugs such as azathioprine, cytarabine, mycophenolate, cyclosporin, and cyclophosphamide can also be used in combination with steroids. It is important to note that steroids can interfere with the 2M antibody test as they decrease the quantity of circulating antibodies in the blood, which may result in a false negative. Therefore, a muscle biopsy may be required to determine the level of inflammation and the severity of fibrosis caused by deteriorating muscle.
MMM can be a recurrent condition and may become more difficult to treat each time. The prognosis declines with subsequent episodes of the disease due to fibrous changes in the muscle. It is very important to give all medications as prescribed and to work closely with a veterinarian. If left untreated, MMM can be fatal as the dog cannot open its mouth to eat or drink.
The outlook for dogs with MMM depends on the degree of inflammation in the muscles and the dog's response to therapy. If MMM is diagnosed early and treatment is started promptly, a dog usually regains normal jaw function and the ability to open and close its mouth without pain.
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MMM can be difficult to treat and may cause relapse
Masticatory Muscle Myositis (MMM) is an immune system disorder where the dog's immune system identifies its own muscle tissue as foreign and attacks it. The masticatory muscles are those involved in chewing. MMM causes these muscles to become swollen and painful, and dogs with MMM are unable to open their mouths without experiencing excruciating pain. They are also unable to eat, chew, or pick up toys.
MMM can be difficult to treat, and relapse is common. The current recommended treatment for MMM is an immune-suppressive dose of corticosteroid medication, usually prednisone, given over a period of months. However, one of the issues with long-term prednisone therapy is muscle atrophy, which can interfere with the return of full muscle function. Corticosteroids can also cause muscle wastage, giving the impression that the dog is getting worse, even if the disease is being controlled. In addition, the underlying cause of MMM is often unknown, making it harder to treat effectively. Suspected triggers include bacterial and/or viral infection, vaccinations, stress, exposure to allergens, reactions to medication, and exposure to environmental toxins.
Dogs who have experienced MMM may relapse, and they may be more difficult to treat during subsequent bouts of the disease. In one study, 6 out of 22 dogs treated for MMM relapsed and required continued administration of low-dose prednisone. Scar tissue can also form within the masticatory muscles, causing permanent problems.
It is important to closely monitor a dog's response to treatment, to ensure that the medication is helping and not causing unwanted side effects. If the underlying cause of MMM can be identified and successfully treated, it may be possible to withdraw medication without the condition relapsing.
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Frequently asked questions
Masticatory Muscle Myositis (MMM) is an autoimmune disease where the dog's immune system identifies and attacks its own masticatory muscles, causing them to become swollen and painful.
The exact cause of Masticatory Muscle Myositis is unknown, but it is believed to be triggered by various factors, including bacterial and viral infections, vaccinations, stress, exposure to allergens or toxins, and reactions to medication. In some cases, it may be associated with cancer.
Symptoms of Masticatory Muscle Myositis include difficulty in moving the jaw, pain, swollen chewing muscles, inability to open the mouth or eat, and sunken eyes. The acute phase may have vague symptoms, while the chronic phase includes muscle shrinkage and progressive muscle wasting.
Masticatory Muscle Myositis can be diagnosed through a specific blood test that measures the level of antibodies attacking the masticatory muscles. A muscle biopsy may also be performed to determine the progression of the disease. Other tests, such as X-rays and ultrasounds, can rule out infections or cancer.
While trauma is not mentioned as a direct cause of Masticatory Muscle Myositis in dogs, it can be a contributing factor. Trauma can lead to inflammation and increased pressure within the inflamed muscle, causing further complications and symptoms.
