Pyomyositis is a rare bacterial infection of skeletal muscle which can result in an abscess (a buildup pocket pus). While pyomyositis is treatable with antibiotics or surgical drainage, it can be fatal if left untreated. Risk factors of pyomyositis include trauma to i.e. physical damage), or overexertion of (i.e. intensive physical activity), skeletal muscles. The cause of pyomyositis and importance of early recognition are explored in this article.

What is Pyomyositis? 

Pyomyositis is a rare bacterial infection in the skeletal muscles (the muscles attached to the bones which allow movement of the body), which typically arises without penetrative trauma or i infection of the adjacent tissue. It is most commonly caused by the bacterium Staphylococcus aureus (S. aureus). S. aureus may live harmlessly on the skin and in the nose (nasal passage). However, if S.aureus enters our bloodstream or muscle tissue - due to heavy exercise, physical trauma, or underlying medical conditions – it can cause infection leading to pyomyositis.

Although pyomyositis is more common in tropical climates such as Africa, South America and the South Pacific, it can also occur in temperate climates. Children and adolescents are at a higher risk of contracting pyomyositis, while people assigned male at birth are more likely to be affected than those assigned female at birth. Individuals with immunocompromised, who have a weaker immune system, are more vulnerable to contracting pyomyositis. However, pyomyositis can occur in all demographics, including otherwise healthy individuals. 

Symptoms & prognosis

Pyomyositis typically progresses through three stages:

Stage 1: Patients experience vague muscle pain and cramps often accompanied by a low fever, as the body attempts to kill the invading bacteria. Due to the generally mild symptoms at this stage, pyomyositis is often not identified until it progresses to the second stage.

Stage 2: One or more abscesses may form in the skeletal muscles. The pain in the muscles may worsen, along with an increased swelling and fever. The abscess may be visible through the skin as a lump at this stage, which may cause mobility issues. For example, an abscess in the legs may cause difficulty walking. Timely medical intervention is essential. If pyomyositis remains untreated, the condition may progress to severe infection.

Stage 3: Extreme pain and high fever. As pyomyositis progresses, the infection may trigger sepsis – an inflammatory response where the body’s immune system begins to damage itself. Ultimately, this may lead to organ failure (loss in function of organs), septic shock (a dangerous drop in blood pressure), and potentially death. Even upon survival, patients may experience a lasting loss of function in the affected muscles or limbs. 

Although pyomyositis can be fatal, early diagnosis and treatment will allow patients to make a quick recovery. Imaging and laboratory tests are used to confirm diagnosis. If caught early, pyomyositis can often be treated with antibiotics. However, surgery may be required to remove the abscesses in more developed pyomyositis.¹

Sports as a risk factor

Pyomyositis can be caused by overuse or physical damage to skeletal muscles, which can occur during intensive physical activity. Pyomyositis has been reported in otherwise healthy teenagers after participation in wrestling, despite no direct hit or penetrative damage to the infected area.^2,3 Similarly, pyomyositis has been recorded in healthy soldiers undergoing physically intensive training.⁴ It is suggested that strenuous exercise causes minor tears and damage to skeletal muscles, increasing the risk of S. aureus infection. However, the exact mechanisms through which vigorous exercise leads to pyomyositis remains unclear and requires further research.

Primary vs secondary infection

Primary infection refers to pyomyositis without a clear path for S. aureus to enter into the bloodstream. Secondary infection refers to where there is a clear pathway of S. aureus entry. 

For example, there is a case of secondary pyomyositis resulting from bacterial infection in chronic paronychia (nail inflammation).⁵ Insect bites may also increase the risk of secondary pyomyositis⁴, which may contribute to the increased prevalence of pyomyositis in tropical climates. 

While most cases of pyomyositis related to sports are classified as primary pyomyositis, acute muscle injuries resulting from vigorous physical activity may lead to secondary infections. Secondary infections may cause a more severe prognosis than primary pyomyositis. However, the methods of diagnosis and treatment of primary and secondary pyomyositis remain the same.

Summary

Pyomyositis is a bacterial infection of the skeletal muscles, most commonly caused by the bacterium S. aureus. The infection generally progresses through three stages, characterised by increased pain and muscle weakness, as well as the formation of one or more abscesses. Although pyomyositis could be fatal or lead to disability, early diagnosis and treatment usually allow patients to make a full, timely recovery. Strenuous physical activity increases the risk of pyomyositis – either directly through acute muscle injuries, or indirectly through muscle damage as a result of overuse. Most pyomyositis resulting from physical exercise are classified as a primary infection; however, some may be considered secondary infections and more severe. Ultimately, more research is needed to fully understand the link between intensive physical activity and pyomyositis.