Everything you need to know including signs, causes, and treatment.
Polymyositis is a type of inflammatory myopathy. This group of diseases includes several types of myopathies, like inclusion body myositis and masticatory muscle myositis (MMM), which only affects the masticatory muscles (the ones you use for chewing). What makes polymyositis different, though, is that it can affect multiple muscles at the same time instead of one specific muscle group or area.
These inflammatory myopathies are often considered autoimmune diseases, which means the body creates autoantibodies, and the immune system attacks itself. Over time, your pup’s muscles become inflamed and irritated, and those autoantibodies break down the muscle tissue as the disease progresses.
Weakness, lethargy, and atrophy are all symptoms of inflammatory myopathies, but those symptoms don’t always stick around. Sometimes inflammatory diseases like polymyositis are acute, meaning that symptoms may show up but go away quickly, while other times, your pup may experience chronic, long-term symptoms. Although polymyositis isn’t curable, treatments are available to help pet owners manage the condition and maintain their pet’s quality of life.
There are several types of polymyositis, and each has different causes. Three main contributing factors may trigger the disease process:
Dogs with polymyositis often show symptoms that their muscles aren’t working normally. A dog with weak, sore muscles may cry or have difficulty when standing up or jumping off of furniture, or they may even whine when you are petting them if the pain is severe. These symptoms can make dogs feel depressed since it’s hard to do the things they normally love, like playing with toys or running around outside.
🚨If you notice any of these signs in your dog, you should take them to a vet immediately.
If your veterinarian believes your pup may have polymyositis, they’ll perform a full physical examination and see what symptoms your pup is showing. Your vet may also recommend diagnostic tests like thoracic X-rays or a blood test with a complete blood count to check for changes in an enzyme called creatine kinase (CK).
This enzyme is found in your skeletal muscles, heart muscle, and brain. When any of those tissues are damaged, they leak CK, which can be used to identify muscle injuries or disease. To make a definitive diagnosis, your vet may take a muscle biopsy to identify any muscle atrophy and inflammation on a microscopic level.
Unfortunately, the outlook for this disease isn’t as good as we’d like it to be. Polymyositis and other canine inflammatory myopathies often lead to euthanasia in affected dogs. But don’t give up hope just yet. In some cases, clinical signs rapidly improve with aggressive treatment.
Pups like this Corgi were given immunosuppressants or high doses of steroids called corticosteroids, and went on to live a long and happy life despite the disease. Options like immunosuppressive therapy may also help to lessen your dog’s immune system response. These treatment options are especially effective in acute conditions. However, only your vet or vet specialist can help you decide the best path for you and your pup.
Although any dog can develop the disease, certain breeds of dogs have an increased risk of polymyositis. These may include:
The first symptoms of myositis may include weakness, lethargy, lameness, or weight loss.
Polymyositis may be treated with high doses of corticosteroids or immunosuppressive therapy.
The life expectancy for your pup will vary depending on the cause of the disease and how well it can be treated. The more severe the disease is when it’s found, the worse the prognosis is likely to be. If you notice your dog displaying any unusual symptoms, take them to a vet immediately.
