Polymyositis: Causes, Symptoms, and Treatment

Medically Reviewed by Zilpah Sheikh, MD on January 16, 2024
6 min read

Polymyositis is a type of disease called an inflammatory myopathy, which means that it irritates the muscles that help you move. Polymyositis also damages nearby tissues, such as the blood vessels that supply oxygen and nutrients to your muscles. 

It usually affects the muscles in your thighs and upper arms. It causes muscle weakness and pain on both sides of your body and makes it hard to do everyday things, such as climbing stairs and getting out of a chair. There’s no cure for this ongoing (chronic) condition, but there are treatments that can help with symptoms.

Polymyositis vs. dermatomyositis

Polymyositis is related to another inflammatory disease called dermatomyositis. Both conditions cause muscle weakness and soreness, but dermatomyositis also causes a rash. This rash could be smooth or scaly and might not be near the weakened muscles. Dermatomyositis also might lead to swelling around your eyes or fingernails.

Polymyositis vs. polymyalgia rheumatica

Polymyositis shares many symptoms with a condition called polymyalgia rheumatica. These conditions can impact muscles on both sides of your body, particularly near the abdomen. The biggest difference is that polymyalgia rheumatica tends to cause muscle pain and stiffness, but polymyositis causes pain and weakness.


No one knows the exact cause of polymyositis. Research shows that it might be similar to an autoimmune disorder. This is when your immune system, which usually protects you against foreign invaders such as viruses, makes a mistake and attacks your own tissues instead. It might be an inherited condition, which means it's passed down through families.

You are at a higher risk of getting polymyositis if you have an autoimmune condition such as:

  • Lupus
  • Rheumatoid arthritis
  • Scleroderma
  • Sjogren’s syndrome

It’s also more common among people with HIV or AIDS.

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.


The symptoms of polymyositis are caused by inflammation (irritation and swelling) in your muscles. The muscle weakness happens on both sides of your body. It usually affects muscle groups closer to the center of your body, such as hips, shoulders, thighs, upper arms, upper back, and neck.

You may have trouble lifting your arms over your head, walking up flights of stairs, rising from a chair, or carrying things. Sometimes, it may be hard to swallow food.

Other symptoms include:

  • Muscle aches
  • Fever
  • Weight loss
  • Fatigue
  • Joint pain
  • Trouble breathing

The condition slowly gets worse over 3-6 months. It's rare, but you could also have polymyositis that comes on very fast.

Polymyositis can become inactive, meaning it will go away and come back. During the inactive periods, you may feel well and have few or no symptoms.



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

Your doctor will take your medical history to rule out other conditions. They may also test your muscle strength.

You may also get tests such as:

  • Blood tests: These can help the doctor spot signs of muscle damage.
  • EMG (electromyography): This is used to check if the patterns of electrical impulses in your muscles are normal or not.
  • MRI (magnetic resonance imaging): This uses a magnet to scan and create images of large areas of your muscle.
  • Muscle biopsy: Your doctor will take a small sample of your muscle for testing to see if the muscle tissue is inflamed.

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

Polymyositis medications

These medications can help with polymyositis:

Corticosteroids. These are the first medicines used to treat polymyositis. They lower inflammation and ease pain.
Drugs that suppress the immune system (immunosuppressants). These medicines help your immune system stop attacking your body's tissues. There are many different kinds of immunosuppressants, such as azathioprine (Imuran® and Azasan®), methotrexate (Rheumatrex® and Trexall®), and rituximab (Rituxan).

Therapeutic treatments

In addition to medicine, your doctor may also suggest some of these therapies, depending on your symptoms:

  • Physical therapy. A physical therapist will guide you through helpful exercises. These exercises will make you stronger and help you move better. 
  • Speech therapy. Polymyositis can weaken the muscles you use to speak. A speech therapist can help with your pronunciation so you can speak more clearly.
  • Dietetic assessment. Over time, muscle weakness can make it difficult to chew and swallow. A nutritionist or registered dietitian can help you plan soft and nutritious meals.

Other treatments

Some people with polymyositis benefit from regular blood infusions. During this procedure, a medical professional will use an IV to give you antibodies called immunoglobulins. These healthy antibodies help protect your muscles from autoimmune attacks.

If you have difficulty moving, braces and other special devices can help.

Complications that might come along with polymyositis include:

Trouble swallowing: This could happen if the muscles in your esophagus are affected. It can lead to weight loss and malnutrition.

Aspiration pneumonia: When you can’t swallow well, you’re more likely to breathe food or liquid (including saliva) into your lungs. This can cause pneumonia.

Breathing problems: If your chest muscles are affected, you could have shortness of breath, and possibly respiratory failure.

Digestion problems: If the muscles in your digestive tract are weakened, you might have problems digesting food. This can also cause malnutrition.

Falls: Weak muscles can cause you to fall and break bones.

Polymyositis is also linked to other health problems. It doesn’t necessarily cause these conditions, but it can increase your risk for them. These include:

  • Heart disease
  • Lung disease
  • Cancer
  • Other connective tissue diseases, such as lupus or rheumatoid arthritis

The prognosis for polymyositis depends on how severe a case you have. Most people respond to treatment and get some of their muscle strength back. Some weakness may remain, and your symptoms could come back. While the condition is rarely life-threatening, you could become disabled if you don’t get proper treatment.

Polymyositis causes your immune system to attack your body's tissues. The main symptoms are muscle weakness and pain, which can make it difficult to climb stairs, lift heavy objects, or carry out other daily activities. There’s no cure, but certain therapies can help manage symptoms and keep your muscles strong. Talk to your doctor about the best treatments for you.

What are the major symptoms of polymyositis?

This condition causes muscle weakness. It usually affects muscles near the abdomen (such as the neck, upper back, upper arms, shoulders, hips, and thighs) across both sides of your body. Muscle aches, fatigue, and fever are other common symptoms.

What is the most common cause of polymyositis?

It’s not clear what causes polymyositis. Some researchers think it might be linked to autoimmune disorders, which cause your immune system to fight your healthy cells as if they were invading germs.

What is the life expectancy of polymyositis?

Polymyositis is a condition you will have your whole life. With the right treatment, you can feel better. But there is a risk of death. About 1 in 10 people who have polymyositis die from it or related diseases.

What does a polymyositis flare-up feel like? 

Polymyositis makes your muscles feel very weak. It might lead to difficulty moving, breathing, or swallowing. You could also feel aches and fatigue.