|Other names: Tropical pyomyositis or Myositis tropicans|
|Transverse T2 magnetic resonance imaging section through the hip region showing abscess collection in a patient with pyomyositis.|
|Diagnostic method||Diagnostic method used for PM includes ultrasound, CT scan and MRI. Ultrasound can be helpful in showing muscular heterogeneity or a purulent collection but it is not useful during the first stage of the disease. CT scan can confirm the diagnosis before abscesses occur with enlargement of the involved muscles and hypodensity when abscess is present, terogenous attenuation and fluid collection with rim enhancement can be found. MRI is useful to assess PM and determine its localization and extension|
Signs and symptoms
The clinical presentation of pyomyositis is as follows:
- Pain in affected muscle
- Abscess formation
In terms of factors that may place an individual at risk of developing pyomyositis we find:
Diagnosis is done via the following manner:
- Pus discharge culture and sensitivity
- X ray of the part to rule out osteomyelitis
- Creatinine phosphokinase (more than 50,000 units)
- MRI is useful
- Ultrasound guided aspiration
CT with IV contrast showing enlargement and heterogeneous hypodensity in the right pectoralis major muscle. A focal abscess collection with gas within it is present medially. There are enlarged axillary lymph nodes and some extension into the right hemithorax. Note the soft tissue and phlegmon surrounding the right internal mammary artery and vein. The patient was HIV+ and the pyomyositis is believed to be due to direct inoculation of the muscle related to parenteral drug abuse. The patient admitted to being a "pocket shooter"
Pyomyositis is most often caused by the bacterium Staphylococcus aureus. The infection can affect any skeletal muscle, but most often infects the large muscle groups such as the quadriceps or gluteal muscles.
Pyomyositis is mainly a disease of children and was first described by Scriba in 1885. Most patients are aged 2 to 5 years, but infection may occur in any age group. Infection often follows minor trauma and is more common in the tropics, where it accounts for 4% of all hospital admissions. In temperate countries such as the US, pyomyositis was a rare condition (accounting for 1 in 3000 pediatric admissions), but has become more common since the appearance of the USA300 strain of MRSA.
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