What Are the Causes of Canine Myositis?

Canine myositis is a condition that damages the muscles through inflammation. Most dogs with myositis develop symptoms quickly, and the symptoms can progress quickly. The most common signs of canine myositis include muscle pain, weakness, difficulty swallowing, stiff walking and muscle swelling or shrinking. If your dog exhibits any of these symptoms, check with a veterinarian as soon as possible to diagnose and treat your pet.

  1. Infection

    • An infection within the dog's muscle can lead to myositis. The infection may be due to a parasite or a virus. Toxoplasma, neospora and hepatozoon are some of the most common parasites that can infect the muscles and cause canine myositis. Although rare, dogs typically acquire toxoplasma parasites from contact with cat feces or raw meat. Neospora parasites are transmitted through contaminated food and meat. Dogs usually acquire hepatozoon parasites through ticks.

    Immune Reaction

    • An abnormal immune reaction can cause myositis in dogs. A dog's immune system can suddenly become overactive and start attacking single muscles or groups of muscles, leading to myositis. This type of myositis is common in the masticatory (chewing) muscles. Veterinary experts are unsure what causes the immune system to become overactive.

    Cancer

    • Canine myositis often occurs just before or after a dog is diagnosed with cancer. The muscle inflammation that causes myositis can turn into cancer or the cancer can trigger an inflammatory response in the muscle. Myositis cases caused by cancer are often difficult to treat because the typical immunosuppressant drugs used to treat the condition can cause undesirable side effects in dogs undergoing cancer treatment. Most veterinarians prefer to treat the cancer rather than myositis to address the most pressing problem first.