Pyomyositis is a rare bacterial infection of the muscle that usually results in an abscess. It’s most common in your thigh muscles. Pyomyositis can be difficult to diagnose, and symptoms usually include fever and muscle pain. Healthcare providers often treat it with antibiotics.


MRI images (top two images) show inflammation in thigh tissue. The CT scan (bottom image) shows an abscess (pyomyositis) that formed near the thigh bone (femur).
In MRI images of patient’s thigh, inflammation looks bright white. On CT, the pyomyositis abscesses look like well-defined shadows.

What is pyomyositis?

Pyomyositis (sometimes called tropical pyomyositis) is a rare and treatable bacterial infection that affects skeletal muscles (the muscles you use to move).

Pyomyositis usually results in an abscess (a swollen area that contains pus) that forms in your muscle. The larger muscles in your legs, especially your quadriceps (thigh muscles), are most commonly affected by pyomyositis, but it can occur in other muscles.


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What bacteria cause pyomyositis?

Approximately 90% of pyomyositis cases are caused by the bacterium Staphylococcus aureus (a common staph infection bacterium).

Most people have Staphylococcus aureus bacteria living on their skin or in their noses. These bacteria only cause problems when they make their way inside your body.

How common is pyomyositis?

Pyomyositis is a rare condition. Healthcare providers used to think pyomyositis could only happen in countries with tropical climates (hence the name “tropical pyomyositis”), but people living in temperate climates, such as North America, can develop it. It’s much less common in temperate climates than it is in tropical climates.


Who does pyomyositis affect?

Pyomyositis can affect anyone at any age. Approximately 35% of pyomyositis cases occur in children, and people assigned male at birth are more commonly affected than people assigned female at birth.

Most people who live in tropical regions and develop pyomyositis are otherwise healthy. People who live in temperate regions and develop pyomyositis often have a weakened immune system (are immunocompromised) or have another serious health condition.

Symptoms and Causes

What causes pyomyositis?

Pyomyositis is most often caused by a bacterium called Staphylococcus aureus (a common staph infection bacterium).

Healthcare professionals aren’t sure exactly how the bacteria get inside your muscle. Heavy exercise, trauma to the muscle and/or certain underlying health conditions are associated with the development of pyomyositis.


What are the symptoms of pyomyositis?

The symptoms of pyomyositis depend on how far the infection has progressed. There are three general stages of pyomyositis.

Stage one of pyomyositis can last 10 to 21 days. Symptoms include:

  • Cramps and aches in the affected muscle.
  • Low-grade fever.

In stage two of pyomyositis, the abscess has formed in the muscle. About 90% of people with pyomyositis are diagnosed at this stage. Symptoms include:

  • Fever and chills.
  • A firm lump under your skin (the muscle abscess).
  • Pain and tenderness in the affected muscle.
  • Mobility issues, like not being able to walk like you usually do if the affected muscle is in your leg.

If pyomyositis is not treated in stage two, it progresses to stage three. Stage three of pyomyositis is serious and life-threatening. Symptoms and complications of pyomyositis include:

  • Extreme pain in the affected area.
  • High fever.
  • Septic shock.
  • Organ damage or failure.

Diagnosis and Tests

How is pyomyositis diagnosed?

Pyomyositis can be difficult to diagnose since the affected muscle tissue is usually deep inside your body. Because of this, you can’t tell from the outside that something is wrong until the abscess gets large enough to cause a noticeable lump under your skin.

The early symptoms of pyomyositis are also common and vague. Fever and muscle soreness could be symptoms of many other conditions. Because of these factors, on average, there’s a 10-day delay in diagnosis from the beginning (onset) of the symptoms of pyomyositis.

Once someone comes to the hospital with symptoms of pyomyositis, an MRI is usually the definitive way to diagnose it. Blood tests and a physical exam can help contribute to the diagnosis.

What tests will be done to diagnose pyomyositis?

Healthcare providers use the following tests to diagnose pyomyositis:

  • Physical exam: Your provider may perform a physical exam to check the affected area for mobility issues, pain sensitivities and an abscess. They may also check other areas of your body to rule out any other possible conditions.
  • Blood tests: Your provider may order a few blood tests to see if your body’s immune system is responding to an infection. This could be a sign of pyomyositis.
  • MRI scan: Magnetic resonance imaging (MRI) is a testing procedure that produces detailed images of the inside of your body without the use of X-rays. Providers often need to use an MRI to make a final diagnosis of pyomyositis. The infected muscle will appear different than other muscles in the images.

Management and Treatment

How is pyomyositis treated?

If pyomyositis is caught early enough, it can usually be treated with just antibiotics. You may take these medications through an IV and/or by mouth as pills. Sometimes a healthcare provider needs to drain the abscess (a swollen area that contains puss) that forms in your muscle from pyomyositis.

If you have pyomyositis and your provider prescribed you antibiotics, be sure to finish taking all the pills as prescribed even if you feel better before you’ve finished them.

How long does treatment for pyomyositis last?

The length of antibiotic treatment for pyomyositis can vary a lot depending on the severity of the infection and how you respond to treatment. Oftentimes healthcare providers use more than one antibiotic to treat pyomyositis. In general, treatment lasts for at least one week but often takes several weeks.


What are the risk factors for developing pyomyositis?

Risk factors for developing pyomyositis include:

  • Living in a tropical climate: Pyomyositis is more common in tropical countries. Approximately 1% to 4% of hospitalizations in tropical countries are due to pyomyositis.
  • Having human immunodeficiency virus (HIV): In approximately half of pyomyositis cases in North America, the person has HIV.
  • Being immunocompromised: People who have a weakened immune system, whether from a medical condition, an organ transplant or from using an immunosuppressive medication, are more likely to develop pyomyositis.
  • Having diabetes: Having high blood sugar (hyperglycemia) from mismanaged diabetes can damage your muscles. People with diabetes may also have weakened immune systems. These two factors make it more likely that someone with diabetes will develop pyomyositis.
  • Heavy exercise or muscle trauma: Vigorous exercise or trauma (damage) to your muscle(s) can trigger pyomyositis.
  • Skin infections: Skin infections, especially staph infections (infections caused by Staphylococcus bacteria), make it more likely that you could develop pyomyositis because the bacteria could spread deeper inside your body to your muscles.
  • Injection drug use: Injecting drugs increases your risk of developing pyomyositis because it can introduce the bacteria that causes pyomyositis into your body.

Outlook / Prognosis

What is the prognosis (outlook) of pyomyositis?

If you’re diagnosed with and treated for pyomyositis soon enough, you can often heal well, and the symptoms go away without any lasting damage to your affected muscle. But if left untreated, pyomyositis can cause serious health issues and can even lead to death. It’s important to contact your healthcare provider if you experience symptoms of pyomyositis.

Can I die from pyomyositis?

Yes, pyomyositis can be fatal. If pyomyositis is not treated in time, the infection can spread to your blood. This can lead to sepsis, which can cause death.

Living With

When should I see my healthcare provider about pyomyositis?

If you’re experiencing symptoms of pyomyositis, such as unexplained fever and persistent pain in your muscle, be sure to contact your healthcare provider.

Additional Common Questions

When should I see my healthcare provider about pyomyositis?

If you’re experiencing symptoms of pyomyositis, such as unexplained fever and persistent pain in your muscle, be sure to contact your healthcare provider.

A note from Cleveland Clinic

Pyomyositis is a rare but serious condition. The good news is that it’s treatable. It can take time to diagnose, so be sure to reach out to your healthcare provider if you’re experiencing symptoms such as an unexplained fever and muscle tenderness, especially if the risk factors for pyomyositis apply to you.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 02/08/2022.

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