Eosinophilic Myositis (Masticatory Muscle Inflammation) in Dogs

  • Occurrence: very rare
  • Location of illness: Head/Neck
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Eosinophilic myositis, also known as masticatory muscle inflammation, is an inflammatory disease of the masticatory muscles in dogs, characterized by an abnormal accumulation of eosinophilic cells, a type of white blood cell. This disease leads to pain, swelling, and loss of function of the affected muscles.

The most important facts at a glance

Eosinophilic myositis, also known as masticatory muscle inflammation, is an autoimmune disease in dogs in which the immune system mistakenly attacks the masticatory muscles, especially the temporalis and masseter muscles. This inflammation is caused by eosinophilic granulocytes, a type of immune cell. Although the exact causes are unknown, genetic predispositions, environmental factors, and infections may play a role. Certain dog breeds, such as the German Shepherd and the Golden Retriever, show a higher susceptibility. Symptoms include exophthalmos, Masseter muscle swelling, difficulty eating and drinking, and Pain when opening the jaw. Diagnosis is made through clinical examinations, blood tests, and imaging procedures. A muscle biopsy can provide a definitive diagnosis. Treatment aims to reduce inflammation and restore muscle activity, usually with corticosteroids. Acute therapy may require high-dose steroids, followed by a gradual reduction in dose. Long-term maintenance therapies may be necessary to prevent relapses. The prognosis is good with early diagnosis and treatment, but left untreated, the disease can lead to permanent muscle changes. Preventive measures are difficult because the causes are not fully understood. However, a balanced diet and regular veterinary check-ups are helpful to promote the dog’s health.

Causes

Masticatory muscle myositis is an autoimmune disease in which the body’s own immune system mistakenly attacks the muscle fibers responsible for chewing. These muscles primarily include the temporalis and masseter muscles. The inflammation is caused by an infiltration of eosinophilic granulocytes, a specific type of immune cell.

The exact causes of eosinophilic myositis are not fully understood, but genetic predispositions, environmental factors, and possibly infections are believed to play a role. In some dog breeds, such as the German Shepherd and the Golden Retriever, there appears to be a genetic predisposition that increases the risk of developing this disease.

Another possible factor could be a reaction to certain medications or vaccines that affect the immune system. However, these associations have not been clearly proven and require further research to fully understand them.

Symptoms

The symptoms of eosinophilic myositis are often sudden and severe. The most common signs include swelling of the masticatory muscles, which prevents the dog from fully opening its mouth. This can lead to Difficulty eating and drinking, sometimes referred to as “trismus”.

In addition, affected dogs may show Pain in the jaw muscles and exhibit Sensitivity to touch. In some cases, Weight loss may also occur because the dog eats less due to the Pain.

Another common symptom is Fever, which is triggered by the inflammatory response in the body. Some dogs also show general signs of discomfort, such as lethargy and decreased activity.

Diagnosis

The diagnosis of eosinophilic myositis is usually made through a combination of clinical examination, blood tests, and imaging procedures. During the clinical examination, the veterinarian checks the masticatory muscles for swelling and pain. A complete blood count may show an increased number of eosinophilic granulocytes, indicating an inflammatory response.

A definitive diagnosis can be made by a muscle biopsy, in which a sample of the affected muscle is taken and examined histopathologically. This examination typically shows an infiltration of eosinophilic cells and other inflammatory changes in the muscle fibers.

In some cases, imaging techniques such as ultrasound or MRI can also be used to assess the extent of the inflammation and possible muscle atrophy. These methods help to rule out other possible causes for the symptoms.

Therapy

The treatment of eosinophilic myositis aims to reduce inflammation and restore muscle activity. This is mainly achieved by administering immunosuppressive drugs such as corticosteroids. These drugs work by suppressing the activity of the immune system, thereby reducing the inflammatory response.

In acute cases, high-dose steroid therapy may be necessary to quickly control symptoms. Once the symptoms have subsided, the dose is gradually reduced to minimize side effects. Long-term, a low-dose maintenance therapy may be necessary to prevent relapses.

In addition to drug therapy, supportive care, such as special diets or nutritional supplements, can be helpful to improve nutrient absorption and support the healing process.

Prognosis and follow-up care

The prognosis for dogs with eosinophilic myositis varies depending on the severity of the disease and the response to treatment. With early diagnosis and appropriate therapy, many dogs have a good prognosis and can lead a relatively normal life.

However, some dogs are at risk of relapse, especially if treatment is stopped too early or the immune system is reactivated. In such cases, long-term maintenance therapy may be necessary to keep the disease under control.

Left untreated, eosinophilic myositis can lead to permanent muscle changes and loss of function, which significantly limits the quality of life of the affected dog.

Prevention

Since the exact causes of eosinophilic myositis are not yet fully understood, there are no specific prevention measures. However, some general measures can help reduce the risk of disease.

A balanced diet and regular veterinary check-ups are important to promote the dog’s overall health and detect potential problems early. In addition, contact with potential triggers of autoimmune reactions, such as certain medications or vaccines, should be discussed with the veterinarian.

In dogs that are genetically predisposed, regular check-ups can help to detect signs of the disease early and start treatment quickly.

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