Dominic Stone
Myositis is a group of inflammatory muscle diseases that can affect dogs. While cancer is a rare cause of myositis, it can be a primary cause or develop secondary to the disease. Myositis can affect a single muscle or an entire group of muscles, such as the masticatory muscles and the eye muscles, and can cause debilitating symptoms. Treatment for myositis in dogs typically involves administering immunosuppressive drugs to counteract the over-excitation of the immune system.
| Characteristics | Values |
|---|---|
| Myositis in dogs | A group of diseases that share an inflammation of the muscle tissue |
| Types of myositis | Masticatory myositis, myositis ossificans, polymyositis |
| Masticatory myositis | Affects the muscles used to chew; caused by an abnormal immune reaction of the body against the muscle |
| Polymyositis | Relatively common; causes muscle weakness and fatigue |
| Causes of myositis | Cancer, infection, inflammation, trauma |
| Diagnosis | Blood test, muscle tissue sample, X-rays, ultrasound |
| Treatment | Corticosteroids, medication, nonsteroidal anti-inflammatory drugs |
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What You'll Learn
Masticatory muscle myositis
Myositis refers to a group of diseases that all involve inflammation of the muscle tissue. This condition can affect only one muscle or an entire group of muscles, such as the masticatory muscles and the eye muscles, and can cause debilitating symptoms.
The symptoms of MMM can vary, but they typically include fever, painful swelling of the temporalis and masseter muscles, and potentially lymphadenopathy. Palpation of the temporalis and masseter muscles leads to pain and difficulty opening the mouth. In the acute phase, the muscles are swollen, and the dog experiences pain and difficulty opening its jaw. In the chronic phase, signs include persistent loss of appetite, weight loss, difficulty opening the jaw, and muscle atrophy. The eyes may also appear sunken as the muscles behind the eyes shrink.
MMM can be diagnosed through a blood test that measures the level of antibodies, specifically the 2M antibody test, and electromyography, which can highlight any abnormal electrical activity in the affected muscles. Other tests, such as blood tests, X-rays, and ultrasounds, can be performed to rule out infections or cancer. Treatment for MMM typically involves the use of immunosuppressive drugs and corticosteroids to counteract the "over-excitation" of the immune system.
While cancer is not commonly the underlying cause of myositis in dogs, it is important to rule it out through appropriate diagnostic tests. In rare cases where cancer is found to be the underlying cause, treatment should be directed against it.
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Eosinophilic myositis
Myositis refers to a group of diseases that all share an inflammation of the muscle tissue. This condition can affect only one muscle or an entire group of muscles, such as the masticatory muscles and the eye muscles, and can cause debilitating symptoms.
In some dogs, eosinophilic myositis is linked to cancer. The inflammation may develop first and turn into cancer over time. Alternatively, cancer elsewhere in the dog's body can trigger an immune reaction that targets the muscles.
The prognosis for dogs with eosinophilic myositis is usually fair, although improvement may take a few weeks to appear. Medications like prednisone and corticosteroids can cause muscle wasting, which may give the impression that the dog's condition is worsening. Therefore, it is important to work closely with a veterinarian to ensure that the dog's condition is improving and that the medications are not causing other issues.
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Extra-ocular muscle myositis
Myositis refers to a group of diseases that all share an inflammation of the muscle tissue. This condition can affect only one muscle or an entire group of muscles, such as the masticatory muscles and the eye muscles, and can cause debilitating symptoms.
Extraocular myositis (EOM) is a rare condition in dogs that affects the extraocular muscles. Young, large-breed dogs are commonly affected, notably the Golden Retriever. Clinical symptoms include acute-onset, bilateral, symmetrical exophthalmos.
The diagnosis of EOM is made through MRI scans, which show increased volume in the extraocular muscles, particularly the medial recti. The condition can also be diagnosed through electromyography, which can highlight any abnormal electrical activity in the affected muscles.
While the exact cause of EOM is unknown, it is believed that shared antigens between the thyroid and extraocular muscles may play a role in the development of the condition. In some cases, cancer may be an underlying cause of myositis in dogs. Inflammation may develop first and turn into cancer over time (pre-cancerous change), or cancer elsewhere in the body may trigger an immune reaction in the muscle (paracancerous effect).
Treatment for EOM is directed towards the underlying cause. If cancer is found to be the cause, therapy is aimed at treating the cancer. The prognosis for dogs with myositis caused by cancer is rather guarded.
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Dermatomyositis
The skin lesions characteristic of dermatomyositis may be crusty erosions, areas of hair loss, or ulcers. These lesions typically occur around the eyes, lips, face, ear flaps, distal extremities, and the tip of the tail. Oral ulcers can also develop, affecting the footpads, nail beds, and mouth, leading to nail abnormalities or loss. Ultimately, scarring may occur in the affected areas, causing difficulty in eating, drinking, or swallowing if the chewing muscles are involved. Additionally, affected dogs may develop a stiff or "goose-step" gait and experience regurgitation, weight loss, and pneumonia due to esophageal dilation.
Diagnosis of dermatomyositis is typically confirmed through a skin and/or muscle biopsy, revealing inflammatory cells. Treatment aims to manage the condition rather than cure it, focusing on controlling symptoms and preventing further skin irritation or damage. Ultraviolet light exposure should be minimised, and activities that may traumatise the skin should be avoided. Medications such as tetracycline, niacinamide, and pentoxifylline can be used to modulate the immune system and improve skin microcirculation. In some cases, anti-inflammatory medications or corticosteroids may be prescribed, but these can cause muscle atrophy.
While rare, cancer can be an underlying cause of dermatomyositis in dogs. In such cases, treatment is directed at addressing the cancer or infection. The prognosis for dogs with dermatomyositis due to cancer is guarded, and euthanasia may be considered if the condition is severe and treatment options are limited.
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Cancer as a primary or secondary cause
Myositis in dogs refers to an inflammatory reaction in the muscle, causing muscle weakness and fatigue. There are several types of myositis, including masticatory muscle myositis, extra-ocular muscle myositis, and polymyositis. While the exact cause of myositis is often unknown, it is believed to be caused by a variety of factors, including heredity, immune-mediated responses, and infections.
Cancer can be a primary or secondary cause of myositis in dogs. In some cases, myositis may be caused by cancer directly affecting the muscles. This can lead to inflammation and pain, resulting in muscle atrophy and dysfunction. Additionally, cancer elsewhere in the dog's body can trigger an immune reaction that targets the muscles, causing myositis. This is known as a paraneoplastic cause.
One type of myositis, eosinophilic myositis, has been specifically linked to cancer in dogs. Eosinophilic myositis is an immune-mediated disease where the dog's immune system attacks the muscle protein of the masticatory muscles, leading to inflammation and pain. It is characterized by swollen masticatory muscles and significant pain when opening the jaw. In some cases, the inflammation may occur first and then develop into cancer over time.
Another form of myositis, polymyositis, can also be caused by cancer. Polymyositis is an inflammatory muscle disorder that affects multiple muscle groups in adult dogs. It is believed to be caused by infectious agents, immune-mediated disorders, or paraneoplastic conditions. While cancer is a less common cause of polymyositis compared to infections, it can still play a role in the development of this type of myositis.
It is important to note that cancer is considered a rare underlying cause of myositis in dogs. However, when cancer is found to be the cause, treatment should be directed towards addressing the cancer. This may involve surgery, immunosuppressive therapy, antibiotics, or antiprotozoal medications, depending on the specific type of myositis and the severity of the condition.
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Frequently asked questions
Myositis is an inflammatory reaction in muscle that can affect a single muscle or an entire group of muscles. There are various types of myositis, each with different causes, ranging from heredity to an immune-mediated response.
Yes, in rare cases, cancer can cause myositis in dogs. It is usually treated by targeting the underlying cause, i.e., cancer.
The symptoms of myositis vary depending on the muscle groups affected. Some common symptoms include jaw discomfort, swallowing difficulties, muscle degeneration, and atrophy.
