What is Pyomyositis?

  • Eleanor Lomax Biological sciences student – MBiol, Durham University
  • Snehanjana Patra M.sc Biotechnology, Amity University
  • Philip James ElliottB.Sc. (Hons), B.Ed. (Hons) (Cardiff University), PGCE (University of Strathclyde), CELTA (Cambridge University) , FSB, MMCA

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Staphylococcus aureus, which is found living on the skin or in the noses of most people. 

Pyomyositis was previously referred to as tropical pyomyositis due to the thinking that the infection could only occur in countries with tropical climates. While this is untrue, instances of pyomyositis are much more common in tropical climates compared to temperate climates.1

However, in more temperate regions those who contract the disease are often immunocompromised through HIV, diabetes, chemotherapy, malnutrition or have another serious health condition such as rheumatoid arthritis.1

Pyomyositis can affect individuals of any age, but around 35% of cases occur in children, and people assigned male at birth (AMAB) are more commonly affected than those assigned female at birth (AFAB). 

Symptoms and stages of pyomyositis 

There are three stages of pyomyositis, which are based on the degree of progression of the infection. 

Stage one – often begins with cramps and aches in the affected muscle (most commonly the thigh) and a slight fever. This stage can last around ten to twenty-one days after initial infection. 

Stage two – begins when an abscess forms in the muscle – this is often the stage at which a diagnosis is made. Symptoms of stage two include fever, a firm lump under the skin, tenderness in the muscle, and issues with mobility. 

Stage 3 – Pyomyositis should be treated as soon as possible, because if left untreated stage three may be reached, which can be life-threatening. Symptoms of stage three are extreme pain, high fever, septic shock, and organ failure. These symptoms can be fatal; therefore, a medical professional should be consulted if you suspect that you may have pyomyositis.

Diagnosis of pyomyositis

Diagnosis of the infection is difficult, because the affected muscle tissue may be deep within the body, with the developing abscess causing no detectable lumps on the surface. Additionally, early symptoms are vague and overlap with many other more common conditions. 

To diagnose pyomyositis, physicians will likely perform a physical examination to check for swelling, pain, or an abscess itself. Blood tests can be run to check for certain antibodies and immune cells that are indicative of the body’s response to infection, as this could be a sign of pyomyositis. You may be asked to undergo an MRI scan to produce detailed images of the muscles. This is often how a final diagnosis of pyomyositis is made.2

If you believe you might have symptoms of pyomyositis – such as persistent pain in your muscles, fever or a lump in a muscle, it is crucial to contact your healthcare provider – because untreated pyomyositis can lead to fatal complications.

Microorganisms that cause pyomyositis

While it cannot be said for certain how the bacterial infection enters the muscles, it is suspected that bacteremic seeding could play a role.3 This involves periodic seedings of the same bacteria into the bloodstream by an existing infection somewhere else in the body. Other factors such as heavy exercise, muscle trauma, and underlying health conditions can lead to the development of the infection.

Approximately 90% of cases of pyomyositis are caused by Staphylococcus aureus (S. aureus). S. aureus is a Gram-positive bacteria that causes a wide variety of clinical diseases, often in community and hospital environments. Treatment of S. aureus-related infections can be difficult due to its ability to adapt and become resistant to many antibiotics. Methicillin-resistant Staphylococcus aureus (MRSA) is an example of a strain that has developed antibiotic resistance.

S. aureus is found in the environment, but also is a normal part of the human flora, as it is located on the skin and in the mucous membranes of healthy individuals. The bacteria do not typically cause troublesome infections in healthy tissue, however, if able to enter the bloodstream, potentially serious infections can occur.4 

Streptococcus pyogenes causes 4-16% of pyomyositis infections and are Gram-positive catalase-negative cocci that occur in pairs or chains, most requiring an enriched media such as blood to survive. Both Streptococci and Staphylococci are members of the normal human body flora, but while Streptococci form chains, Staphylococci form clumps and do not require an enriched media such as blood to thrive.5

There is in existence an even rarer, potentially lethal necrotising variant of pyomyositis from E. coli that has been sparsely reported with less than 20 cases reported in the literature.6

Treatment options 

Early pyomyositis can be treated with antibiotics such as clindamycin or trimethoprim-sulfamethoxazole plus penicillin, as this inhibits bacterial toxin production and can enhance phagocytosis of the bacteria

When bacteria enter the muscle, cytokines are released which triggers the immune system to send white blood cells to fight the infection in the affected area. This causes some nearby tissue to die, creating a hole that fills with pus and forms an abscess. This is a defensive reaction of the tissue to prevent the spread of infectious material to other parts of the body.

However, once an abscess has formed, percutaneous or open surgical drainage is required, and aspiration (sucking out fluid) with a large bore needle may be necessary to locate and drain the abscess due to its depth within the muscle tissue. 

Other medications such as steroids can be taken to prevent your immune system from attacking your body and to reduce swelling. 

After any of these treatments, it is likely that a doctor will also suggest physiotherapy in order to improve muscle strength and encourage you to regain mobility and stay active. 

If the infection becomes severe or other therapies have not improved the condition, immunoglobulin therapy, which uses antibodies taken from donated blood, may be offered to boost the immune system. 

Complications and long-term effects

Muscle necrosis (death of muscle tissue) can occur in an individual with pyomyositis if too little blood is able to flow into the tissue. Necrosis cannot be reversed and when large areas of tissue die due to this lack of blood supply the condition is referred to as gangrene.9

Although most individuals make a good recovery from pyomyositis, long-term effects can occur. Some individuals may never regain their original muscle strength and function; therefore, physiotherapy is always recommended to try to combat this. 

Occasionally, pyomyositis can spread to multiple, different muscles, potentially causing problems with breathing and swallowing when the muscles involved in these processes become weak. As well as this, inflammation that has spread to the lungs can cause scarring, thereby impacting the function of the lungs.10 Children who contract pyomyositis can also develop complications such as pneumonia, arthritis, and osteomyelitis.11

Pyomyositis is rare and the prognosis for recovery is good if treated early and properly. If left untreated, 0.5-2% of individuals die from the infection. After surgical drainage, there is the possibility that the infection could return. However, following your doctor’s advice about your antibiotic consumption schedule is the best way to reduce the likelihood of recurrence.

Preventative measures

There are few recommendations concerning the prevention of pyomyositis because its mechanism of infection is still largely unknown. However, it is believed that the nasal passages should be examined in individuals who have a history of pyomyositis or Staphylococcal infections and a topical mupirocin nasal formulation can be prescribed to prevent nasal infections of S. aureus.11

Although there is no guaranteed way of preventing pyomyositis, there are steps that can be taken to strengthen muscles. These include regular moderate exercise, a balanced diet, and stress management. 

Hand hygiene is considered one of the most important ways to reduce the risk of infection by S. aureus, particularly in hospital settings. Thorough hand washing using an antibacterial soap removes germs from the hands and reduces the likelihood that they will enter the body through touching the eyes or the mouth, this also reduces the likelihood of passing germs onto others. 

Summary

Pyomyositis is a rare bacterial infection that is most often caused by Staphylococcus aureus but can be caused by other types of bacteria. It mostly occurs in skeletal muscles such as those in the thigh. 

It can be difficult to diagnose, as symptoms begin with a fever, muscle cramps, and mobility issues, which are indicative of many other more common conditions. It is more likely to be diagnosed when later on an abscess forms within the muscle and a lump is detectable under the skin. 

Pyomyositis is much more common in tropical climates compared to temperate climates, those who develop pyomyositis in temperate climates are often already immunocompromised e.g., through HIV. Pyomyositis is treated with antibiotics, and once an abscess has formed, surgical drainage is required to remove pus from the muscle. If left untreated, complications such as muscle necrosis, septic shock, and death can occur. However, most individuals recover well from the infection. There is no guaranteed way of preventing pyomyositis, but regular moderate exercise, a balanced diet, and stress management are good ways to develop strong muscles.

References

  1. Chattopadhyay B, Mukhopadhyay M, Chatterjee A, Biswas PK, Chatterjee N, Debnath NB. Tropical Pyomyositis. N Am J Med Sci [Internet]. 2013 [cited 2024 May 5]; 5(10):600–3. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3842701/.
  2. López Fernández L, Jiménez Escobar V, Sáenz Moreno I, Gallinas Maraña E, Cuadrado Piqueras L. Acute pyomyositis: Diagnosis and treatment of 3 cases in a secondary hospital. An Pediatr (English version) (Barc) [Internet]. 2021 [cited 2024 May 5]; 95(6):467–8. Available from: http://www.analesdepediatria.org/en-acute-pyomyositis-diagnosis-treatment-3-articulo-S2341287921001812.
  3. Radcliffe C, Gisriel S, Niu YS, Peaper D, Delgado S, Grant M. Pyomyositis and Infectious Myositis: A Comprehensive, Single-Center Retrospective Study. Open Forum Infect Dis [Internet]. 2021 [cited 2024 May 5]; 8(4):ofab098. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8047863/.
  4. Taylor TA, Unakal CG. Staphylococcus aureus Infection. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 [cited 2024 May 5]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK441868/.
  5. Barchi L, Fastiggi M, Bassoli I, Bonvicini F, Silvotti M, Iughetti L, et al. Pyomyositis associated with abscess formation caused by streptococcus pneumoniae in children: a case report and review of literature. Ital J Pediatr. 2023; 49(1):73. Available from: https://pubmed.ncbi.nlm.nih.gov/37316947/
  6. Das S, Shaikh O, Gaur NK, Vijayakumar C, Kumbhar U. Fulminant Necrotizing Pyomyositis Tropicans. Cureus [Internet]. [cited 2024 May 5]; 14(1):e21767. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8890598/.
  7. Chen P-L, Chen Y-W, Ou C-C, Lee T-M, Wu C-J, Ko W-C, et al. A Disease Model of Muscle Necrosis Caused by Aeromonas dhakensis Infection in Caenorhabditis elegans. Front Microbiol [Internet]. 2017 [cited 2024 May 5]; 7:2058. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5209350/.
  8. Chaudhary D, Aggarwal T, Pannu AK. Staphylococcus aureus pyomyositis and septic lung emboli. CMAJ [Internet]. 2022 [cited 2024 May 5]; 194(4):E126. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8900776/.
  9. Verma S. Pyomyositis in Children. Curr Infect Dis Rep [Internet]. 2016 [cited 2024 May 5]; 18(4):12. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7102239/.

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Eleanor Lomax

Biological sciences student – MBiol, Durham University

Eleanor is a student of biological sciences who has several years of involvement in working with knowledgeable researchers to write and publish medical articles. She has a range of experience educating others about biology and medicine through her role as a STEM ambassador and through internships with the Durham university bioscience department.

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