ContentsSynopsisCodesLook ForDiagnostic PearlsDifferential Diagnosis & PitfallsBest TestsManagement PearlsTherapyDrug Reaction DataReferencesView all Images (4)
Other Resources UpToDate PubMed


Print Images (4)
Contributors: Neil Mendoza MD, Paritosh Prasad MD
Other Resources UpToDate PubMed


Pyomyositis is an infection of the skeletal muscle most commonly caused by Staphylococcus aureus.

The epidemiology of this infection is different in the tropics where it affects children and younger adults, often due to trauma, than in temperate regions where it is seen in adults often with intravenous drug use or with immunodeficiency such as human immunodeficiency virus (HIV) infection, hematologic malignancies, steroid use, chemotherapy use, and alcoholic liver disease.

While the most common pathogen causing this infection is S. aureus, other pathogens that have been implicated include group A Streptococcus and the enteric gram-negative organisms. Infections are typically due to a single organism, but can also be polymicrobial.

The course of infection is typically subacute. Initially, there is mild pain and local swelling. Fever and increasing pain at the site of involved muscle follows. It is at this point (10-21 days after the first symptoms of infection) that most patients present, and it is at this stage that pus can be aspirated from the infected muscle. Finally, signs of major systemic illness and sepsis manifest. Throughout the course of infection, erythema, fluctuance, and tenderness of the involved site evolve and become more prominent. Leukocytosis is common.

Imaging modalities (especially magnetic resonance imaging [MRI]) are important in the diagnosis of this infection and may help identify areas of infection that would benefit from surgical drainage.


M60.009 – Infective myositis, unspecified site

29689003 – Infective myositis

Look For

Subscription Required

Diagnostic Pearls

Subscription Required

Differential Diagnosis & Pitfalls

  • Depending on the site of pyomyositis, the location of pain may mimic osteomyelitis, septic arthritis, appendicitis, or diverticulitis.
  • Early in the course, muscle strain may be suspected, especially if the patient recalls vigorous exercise or injury.
  • If there has been trauma to the muscle group, hematoma might be suspected.
Imaging modalities including MRI are very helpful in identifying the muscle inflammation or abscess that defines pyomyositis and may help eliminate some of the entities in the above differential diagnosis.

Best Tests

Subscription Required

Management Pearls

Subscription Required


Subscription Required

Drug Reaction Data

Below is a list of drugs with literature evidence indicating an adverse association with this diagnosis. The list is continually updated through ongoing research and new medication approvals. Click on Citations to sort by number of citations or click on Medication to sort the medications alphabetically.

Subscription Required


Subscription Required

Last Updated: 01/25/2016
Copyright © 2019 VisualDx®. All rights reserved.
Print 4 Images
View all Images (4)
(with subscription)
Pyomyositis (Stage 1) : Edema, Muscle cramp, ESR elevated, Low grade fever, WBC elevated
Clinical image of Pyomyositis
Copyright © 2019 VisualDx®. All rights reserved.