Infectious Myositis

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Overview


By [Chris Santucci]

Infectious Myositis is an infection that can be caused by microbes of all domains. It is characterized by muscle inflammation and usually is seen in voluntary muscle. [1] It is an uncommon infection and is very diverse in the way it can come about. Infectious myositis can result from surgeries in which incisions allow microbes in, wounds that are contaminated, injectable drug needles that are unsterilized, undercooked foods, among other reasons, making it difficult to detect and prevent at first. Immunocompromised individuals are always at risk for myositis. Myositis is not caused by one microbial group, but rather can be caused by a broad range of microbes including bacteria, fungi, viruses, and parasites. The infection can be polymicrobial, but in many cases one organism dominates the infected site. In order to identify the specific microbe responsible, culturing is necessary. This page hopes to express the vast array of infection and treatments associated with the main types of myositis.

To the right is a photograph depicting a patient with myositis of the gastrocnemius. This is a typical case of myositis in voluntary skeletal muscle.

MRI of myositis of the gastrocnemius and multiple abscesses of the posterior compartment caused by community-acquired methicillin-resistant Staphylococcus. [1].


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Legend/credit: MRI of myositis of the gastrocnemius and multiple abscesses of the posterior compartment caused by community-acquired methicillin-resistant Staphylococcus. [8].
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Bacterial Infectious Myositis


Bacteria are the most common domain that can infect muscle leading to myositis from infection according to the literature. Staphylococcus aereus and Streptococcus strains, both gram-positive and typically facultative anaerobes, are the most common bacteria causing agents of myositis and are categorized into their own type of myositis. Some cases of bacterial myositis are polymicrobial, especially when infections are contaminated with soil. In events of bacterial myositis, it is necessary to culture on differential media and use gram staining to determine the bacteria responsible for the infection in order to treat the infection. Pyomyositis, psoas abscess, S. aereus myositis, group A and group B streptococcal myositis, Clostridial gas gangrene, and nonclostridial myositis are the distinctive categories of bacterial myositis. [3]

Pyomyositis

Pyomyositis, also known as tropical myositis because it is found often in tropical climates, is a bacterial infection due to hematogenous spread (spread through the blood stream) mainly caused by Staphylococcus aereus that is only present in one muscle group. [4]. This infection is often seen in children, but not always. [5] In fact, it can be found in people of all ages and is becoming more prevalent in the United States in the past 40 years. [6]
It was discovered that immunocompromised individuals, such as those with HIV, are more likely to acquire pyomyositis. [7] This can be attributed to many reasons, but most importantly the fact that S. aureus grows much more easily in immunocompromised people that have a weaker defense mechanism [8] Pyomyositis cases, in general, have increased since the HIV epidemic has broken out. [9]


Since pyomyositis occurs in single muscle groups, it is no surprise that cases of pyomyositis have been identified in bodybuilders who use anabolic steroids, known to increase athletic performance. Anabolic steroids are commonly injected into sites in which the athlete desires mass gain. [10] ,which poses more risks than just the detrimental effects anabolic steroids have on healthy individuals who do not need them for health reasons. In a case study, one bodybuilder began to have pain in his right arm and was diagnosed with pyomyositis of brachial biceps. The diagnosis was a result of culturing of a sample of the patient’s steroid needle, which was positive for S. aereus, which can be treated with antibiotics. [11] Another bodybuilding, anabolic steroid-user with the same diagnosis of S. aereus pyomyositis in the brachial biceps underwent surgical cleaning and a Penrose drain (essentially a tube that drains fluid after surgery) was used in addition to antibiotic treatment. [12] In a third similar case, a steroid user was found to have pyomyositis of the brachial biceps and ipsilateral triceps with culturing revealing presence of S. viridians, which was treated with antibiotics. A picture of magnetic resonance imaging of the bicep can be seen to the right.

Magnetic resonance imaging of myositis by S. viridians in the bicep of an anabolic steroid user. [2].

In all three cases, the athletes were able to return to full athletic activity within 42 days. Since anabolic steroids in bodybuilders, among other drugs administered without clinical approval, are injected in a nonsterile site, the site at which the steroids are injected is at high risk for infections i.e. pyomyosits.


Psoas Abscess

A psoas abscess is essentially pyomyositis that occurs specifically in the psoas muscle in the lower back and is caused by many different bacteria, but most commonly Mycobacterium tuberculosis and S. aereus. It is classified separately because pyomyositis in the psoas muscle is more common than any other muscle group. Primary psoas abscesses occur directly in the psaos muscle, but secondary infections can occur from nearby bacterial infection that spreads into the psoas muscle. [13] The psoas muscle is subject to infection as a result of its positioning in the body. Because it is very close to the spine, which is subject to infection, bacteria can easily move through the blood and into the psoas muscle. In addition, the muscle is close to other structures like the colon, appendix, jejunum, and pancreas, which can all spread bacteria through blood to the psoas. [14] Psoas abscesses are usually treated with anti-staphylococcal antibiotics because S. aereus is the most common cause, but other antibiotics suited for gram-negative and anaerobic bacteria are necessary in other situations when the infection is polymicrobial. [15]


Primary psoas abscesses are typically caused by S. aereus as seen in cases of pyomyositis, since it is localized in one muscle group. [16]In the same way as other types of pyomyositis, primary psoas abscesses are commonly seen in heroin or other injectable drug users, and immunocompromised individuals are more susceptible. [17] To the right is a CT scan of a psoas abscess by Group A streptococci in a patient with HIV. In rare cases, primary psoas abscesses can be due to S. pneumoniae, S. milleri, and other streptococci as well as gram-negative bacteria including Escherichia coli, Pseudomonas, Haemophilus, and Pasteurella. [18]

Secondary psoas abscesses are more versatile as they result from bacterial spread from other nearby organs and muscles. S. aereus as well as Mycobacterium tuberculosis, a gram-positive Actinobacteria pathogen that typically causes tuberculosis [19] are the most common causes and are easily spread through vertebrae and other nearby structures into the psoas muscle. S. aereus and Mycobacterium tuberculosis often infect the psoas muscle in patients who have vertebral osteomyelitis, which is a bacterial infection of the spine. [20] In addition, Pott’s disease, which is a Mycobacterium tuberculosisinfection of the spine tends to cause a secondary psoas abscess. Secondary psoas abscesses in many cases, though have more than one microbe involved. Gram-negative E.coli, Enterobacter, Salmonella, and Klebsiella and anaerobes like Clostridium and Bacteroides can all be responsible for secondary psoas abscesses. [21] Because of this, many different antiobiotics may be needed for treatment. Individuals with cancers, appendicitis, and other gastrointestinal infections are more susceptible to secondary psoas abscesses as bacteria can be spread into the psoas from their preexisting conditions [22]


In an interesting case, a 45-year-old female was diagnosed with a psoas abscess in the right psoas muscle that was first identified through sharp pain in the lower back and thigh. She was not a drug user, but had a job that involved labor and heavy lifting. After an MRI that was negative for vertebral osteomyelitis, a CT scan of the lumbar spine was performed identifying a psoas abscess and can be seen to the left.

CT scan of psoas abscess by Streptococcus pyogenes in HIV patient. [3].

Upon culturing, gram-positive cocci were found and were further identified as methicillin-sensitive S. aereus allowing antiobiotic treatment with methicillin to subdue the infection. [23]


Bacterial Myositis
Bacterial Myositis is different from pyomyositis and psoas abscesses because it is unlocalized, and usually does not present a large abscess. It is much less common than pyomyositis and psoas abscesses. Bacterial Myositis is usually caused by Streptococcus, although other gram-positive bacteria can lead to myositis including Clostridium species, including the bacteria that causes gas gangrene [24] Clostridium myositis (gas gangrene) caused by C. perfringens is an infection where necrosis is present and usually results from wounds contaminated with soil, since Clostridium species live in soil, and can also be due to surgeries and intravenous drug use. Rare cases of gas gangrene can result with no skin breakage, but typically are due to gastrointestinal problems. [25] When in low-oxygen environments, like inside muscle, Clostridium convert from their spore shape to their vegetative structure and produce toxins that can cause tissue damage. Although gas is found in tissue and is excreted from the wound of most patients with gas gangrene (giving it its name), not all patients will experience gas bubbles, making those cases difficult to diagnose. Commonly, C. perfringens-infected muscle will be unable to contract and there will be less blood from the wound than in uninfected tissue, yielding physical signs of gas gangrene, and when doing culture diagnostics, the absence of neutrophils and presence of gram-positive bacilli indicate the possibility of gas gangrene. In treatment of cases of contaminated wounds, antibiotics that can kill gram-negative organisms as well as gram-positive organisms like C. perfringens must be used because of other organisms potentially contributing to the infection. [26]

CT scan of psoas abscess by Streptococcus aereus. [4].


MRI of Group B_streptococcal myositis in right rectus muscle identified with the arrow. [5].


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Myositis by Fungi

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Myositis by Viral infection

MRI of bicep parasitic myositis by Taenia solium. [6].


Parasitic Myositis

Micrograph of the unidentified fungi in a case of fungal myositis. [7].


Conclusion

References

  1. ↑ [Crum-Cianflone, Nancy F. “Bacterial, Fungal, Parasitic, and Viral Myositis.” Clinical Microbiology Reviews 21.3 (2008): 473–494. PMC]
  2. ↑ Bartlett et al.: Oncolytic viruses as therapeutic cancer vaccines. Molecular Cancer 2013 12:103.
  3. ↑ [Crum-Cianflone, Nancy F. “Bacterial, Fungal, Parasitic, and Viral Myositis.” Clinical MicrobiologyReviews 21.3 (2008): 473–494. PMC]
  4. ↑ [Crum-Cianflone, Nancy F. “Bacterial, Fungal, Parasitic, and Viral Myositis.” Clinical Microbiology Reviews 21.3 (2008): 473–494. PMC]
  5. ↑ [Horn, C. V., and S. Master. 1968. Pyomyositis tropicans in Uganda. East Afr. Med. ]
  6. ↑ [Levin, M. J., and P. Gardner. 1971. “Tropical” pyomyositis: an unusual infection due to Staphylococcus aureus. N. Engl. J. Med. 284:196-198.]
  7. ↑ [Crum-Cianflone, Nancy F. “Bacterial, Fungal, Parasitic, and Viral Myositis.” Clinical Microbiology Reviews 21.3 (2008): 473–494. PMC]
  8. ↑ [Widrow, C. A., S. M. Kellie, B. R. Saltzman, and U. Mathur-Wagh. 1991. Pyomyositis in patients with the human immunodeficiency virus: an unusual form of disseminated bacterial infection. Am. J. Med]
  9. ↑ [Christin, L., and G. A. Sarosi. 1992. Pyomyositis in North America: case reports and review. Clin. Infect. Dis. 15:668-677]
  10. ↑ [Filho, Nivaldo Souza Cardozo et al. “PYOMYOSITIS IN ATHLETES AFTER THE USE OF ANABOLIC STEROIDS - CASE REPORTS.” Revista Brasileira de Ortopedia 46.1 (2011): 97–100. PMC]
  11. ↑ [Filho, Nivaldo Souza Cardozo et al. “PYOMYOSITIS IN ATHLETES AFTER THE USE OF ANABOLIC STEROIDS - CASE REPORTS.” Revista Brasileira de Ortopedia 46.1 (2011): 97–100. PMC]
  12. ↑ [Filho, Nivaldo Souza Cardozo et al. “PYOMYOSITIS IN ATHLETES AFTER THE USE OF ANABOLIC STEROIDS - CASE REPORTS.” Revista Brasileira de Ortopedia 46.1 (2011): 97–100. PMC]
  13. ↑ [ Crum-Cianflone, Nancy F. “Bacterial, Fungal, Parasitic, and Viral Myositis.” Clinical Microbiology Reviews 21.3 (2008): 473–494. PMC]
  14. ↑ [ Crum-Cianflone, Nancy F. “Bacterial, Fungal, Parasitic, and Viral Myositis.” Clinical Microbiology Reviews 21.3 (2008): 473–494. PMC]
  15. ↑ [Tomich, Eric B., and David Della-Giustina. “Bilateral Psoas Abscess in the Emergency Department.” Western Journal of Emergency Medicine 10.4 (2009)]
  16. ↑ [Gruenwald, I., J. Abrahamson, and O. Cohen. 1992. Psoas abscess: case report and review of the literature. J. Urol]
  17. ↑ [Santaella, R. O., E. K. Fishman, and P. A. Lipsett. 1995. Primary vs secondary iliopsoas abscess. Presentation, microbiology, and treatment. Arch. Surg]
  18. ↑ [Crum-Cianflone, Nancy F. “Bacterial, Fungal, Parasitic, and Viral Myositis.” Clinical Microbiology Reviews 21.3 (2008): 473–494. PMC]
  19. ↑ [MicrobeWiki, Mycobacterium tuberculosis]
  20. ↑ [Crum-Cianflone, Nancy F. “Bacterial, Fungal, Parasitic, and Viral Myositis.” Clinical Microbiology Reviews 21.3 (2008): 473–494. PMC]
  21. ↑ [Santaella, R. O., E. K. Fishman, and P. A. Lipsett. 1995. Primary vs secondary iliopsoas abscess. Presentation, microbiology, and treatment]
  22. ↑ [van den Berge, M., T. de Marie, S. Kuipers, A. R. Jansz, and B. Bravenboer. 2005. Psoas abscess: report of a series and review of the literature. Neth. J. Med]
  23. ↑ [Tomich, Eric B., and David Della-Giustina. “Bilateral Psoas Abscess in the Emergency Department.” Western Journal of Emergency Medicine 10.4 (2009)]
  24. ↑ [Adams, E. M., S. Gudmundsson, D. E. Yocum, R. C. Haselby, W. A. Craig, and W. R Sundstrom. 1985. Streptococcal myositis. Arch. Intern. Med.]
  25. ↑ [ El-Masry, S. 2005. Spontaneous gas gangrene associated with occult carcinoma of the colon: a case report and review of the literature. Int. Surg]
  26. ↑ [Crum-Cianflone, Nancy F. “Bacterial, Fungal, Parasitic, and Viral Myositis.” Clinical Microbiology Reviews 21.3 (2008): 473–494. PMC]



Authored for BIOL 238 Microbiology, taught by Joan Slonczewski, 2017, Kenyon College.

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