Myositis is defined as the inflammation of muscle in animals. This potentially serious and painful condition can be found in dogs and is often an early indication of some kind of illness, including in some cases cancer. Myositis can affect one muscle or a group of muscles, often those around the jaw, eyes, and face associated with chewing (masticatory myositis). This condition can affect a dog's ability to eat and drink and should be taken quite seriously. The causes of myositis are varied. Treatment plans usually involve some combination of immunosuppressive drugs and pain medication.
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Common Causes
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The causes of myositis are varied, ranging from the easily treatable to the potentially life-threatening. Myositis can occur as a response to some kind of infectious agent such as a parasite or virus within a muscle or muscle group. Parasites that cause myositis include toxoplasma, neospora, and hepatozoon. Myositis can also be caused by an abnormal immune reaction that the body directs at the muscle or muscle group. In effect, the immune system becomes overexcited and attacks the muscle.
Association with Cancer
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Myositis is also a relatively common sign that your dog may be experiencing the onset of cancer. The inflammation of myositis can become cancerous over time, or cancer in another part of the body can trigger a heightened immune response that leads to myositis. A vet's typical response is to treat the cancer not the myositis because the usual immunosuppresant drugs used to treat the inflammation can result in undesirable side effects. Most vets would also consider cancer the higher priority because it is potentially fatal. Throat and mouth cancers are often accompanied by some degree of myositis as well.
Treatments
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Myositis is usally treated with immunosuppressive drugs that help counteract the over-excitement of the immune system. Vets usualy prescribe high doses of the steroid prednisolone to suppress the immune system. Other non-steroid medications such mycophenolate, cyclosporin, asazathioprine, cytarabine, and cyclophosphamide can also be used. The aim of most treatment plans is to gradually lower the dosage and return the dog to normal without any dependency on the drug. This result is difficult to achieve, though, and small doses are often necessary to keep the condition under control. Unfortunately, immunosuppressives are often accompanied by undesirable side affects because they leave the immune system weakened and the body prone to infection. Always follow your vet's instructions regarding dosage and frequency as these are crucial to the animal's recovery.
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