Myositis in Dogs

Myositis in dogs is a muscle disorder in which noncancerous bony deposits appear in the muscles and connective 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.

Myositis in dogs can be a serious and painful condition and may be an early indicator that the animal is ill in some other way. The cause is unknown. As with many types of myositis, without early and aggressive treatment, muscle loss can cause severe atrophy and muscle dysfunction.

The disorder frequently affects tissues near the hip joint in Doberman Pinschers.

Tpyes of Myositis in Dogs

There are two pathologies that cause myositis in dogs: polymyositis and myositis of the chewing muscles

Polymyositis

Polymyositis is a type of inflammatory myopathy that is shown as a more generalized aspect of muscle involvement. First, it damages the muscles of the extremities, especially in adult races. Generally, it is discovered through exercise when the dog shows weakness, fever or the beginning of muscular atrophy.

Matisticatory Myositis

For its part, the myositis of the chewing muscles, also called eosinophilic or matisticatory myositis, is an inflammatory disease that damages the animal’s chewing muscles, that is, the temporal muscles (masseter and pterygoid), causing immobility in them.
There are two types of these pathologies, chronic and acute. In the chronicle, muscle atrophy predominates; In the acute, its most common symptoms are pain and fever.

Causes Myositis in Dogs

The inflammation in the muscle can be due to:

• Response of the body to an infectious agent (parasite or virus) within the muscle (Infectious Myositis).
• Abnormal immune reaction of the body directed against the muscle (Immune-mediated Myositis). In Masticatory Muscle Myositis the body produces antibodies that target parts of muscle that are only found in the masticatory muscles. No-one knows why the immune system suddenly becomes ‘over-excited’ and attacks the muscles in this way in some animals.
• Myositis in dogs may also be associated with cancer. Inflammation may develop first and turn into cancer with time (pre-cancerous change), or cancer elsewhere in the body may trigger an immune reaction to the muscle (paracancerous effect).

Symptoms of Myositis in Dogs

Swollen, painful masticatory (chewing) muscles and an inability to open the mouth (trismus) are clinical signs of the disorder. Affected dogs are not able to pick up a ball or eat without experiencing severe pain. In the early stages of the disease, the muscles that are used for eating and chewing appear swollen. As the disease progresses, these muscles begin to atrophy, or waste away. Sometimes the eyes appear sunken, or, less commonly, they seem to protrude.

other signs include

• Stiff walking
• Muscle pain
• Muscle weakness
• Swelling in muscles
• Loss of muscle
• Difficulty swallowing
• Regurgitation
• Breathing problems
• Skin lesions

Treatment of Myositis in Dogs

Once a positive diagnosis of myositis is reached, treatment attempts to counteract the immune system activity against the muscles by using immunosuppressive medications to return the system to normal. High doses of steroids, such as prednisolone, may be prescribed, as well as immunomodulators like cyclosporine, cyclophosphamide, cytarabine, azathioprine, or mycophenolate.

When the myositis is controlled, doses are decreased slowly in the hopes there is not a relapse. The goal is to eliminate all drugs, but generally a low dose of medication is continually needed to keep the symptoms from returning.