What Is Polymyositis?

Polymyositis is a rare form of arthritis that causes muscle weakness and pain. There’s no cure for this ongoing (chronic) condition, but there are treatments that can help with symptoms.

Causes

No one knows what the exact cause is. But doctors do know that it’s an autoimmune condition, which means the body can attack its own tissues. This is what causes the problems.

It’s more common in people with other autoimmune diseases like lupus and rheumatoid arthritis. It’s also more common among people with HIV.

Most people who have polymyositis get diagnosed between the ages of 30 and 60. It’s very rare in children, and it affects women more often than men.

Symptoms

The symptoms of polymyositis are caused by swelling or pain in the muscles. The muscle weakness affects both sides of the body equally.

The condition tends to target the muscle groups that are closest to the trunk of the body -- the hips, shoulders, thighs, upper arms, upper back, and neck.

If you have it, you may notice you have trouble lifting your arms over your head, walking up flights of stairs, rising from a chair, or carrying things. In some cases, it may be hard to swallow food, but this is unusual.

You may or may not have pain in the areas where the muscles are weak. Over time, the muscles may atrophy, meaning they waste away or become less bulky. The condition often worsens slowly, and you might not notice symptoms for months.

Muscle weakness may be one of the first symptoms you do notice. You may also feel you just can’t do all the things you used to. You may also have:

  • Fever
  • Weight loss
  • Fatigue
  • Joint pain
  • Raynaud’s phenomenon, a condition in which the fingers or toes become very cold and discolored due to blood-flow problems.

Diagnosis

There are no simple tests to diagnose polymyositis. It often takes time before doctors know for sure you have it.

Your doctor will consider your medical history, and your family’s, to rule out other conditions. You may also get tests such as:

  • EMG (electromyography), which checks to see if the patterns of electrical impulses in the muscles are normal or not)
  • Muscle biopsy, which can show whether or not the muscle tissue is inflamed. Your doctor will take a small sample of your muscle for testing. You may need to get an MRI to help your doctor find a good spot to biopsy.
  • Certain blood tests, for signs of muscle damage

Continued

Treatment

Polymyositis is a chronic condition. That means that once you have it, it sticks around. But there are ways to help manage it.

Common treatments include:

  • Steroids. These help with muscle inflammation, reduce pain, and even increase muscle strength. But steroids can have many side effects, so when your doctor prescribes them, he’ll keep an eye on you.
  • Drugs that suppress the immune system. You may take these with steroids, or on their own if steroids don’t help.
  • Speech therapy. If you have trouble swallowing, this can help strengthen those muscles.

Ask your doctor about any questions you may have, and for other ways to make your life easier.

WebMD Medical Reference Reviewed by David Zelman, MD on September 19, 2016

Sources

SOURCES:

Arthritis Foundation: “Myositis.”

Muscular Dystrophy Association: “Polymyositis

National Institute of Neurological Disorders and Stroke. “NINDS polymyositis information page.”

National Organization for Rare Diseases: “Polymyositis.”

Myositis Association: “Polymyositis,” “Practical concerns,” and “Patients living with myositis.”   

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