Pyomyositis

Pyomyositis
File:Pyomyositis MRI.jpg Transverse T2 magnetic resonance imaging section through the hip region showing abscess collection in a patient with pyomyositis.
Classification and external resources
Specialty
ICD-10	M60.0
ICD-9-CM	040.81, 728.0
DiseasesDB	29474
Patient UK	Pyomyositis
MeSH	D052880
Orphanet	764

Pyomyositis, also known as tropical pyomyositis or myositis tropicans, is a bacterial infection of the skeletal muscles which results in a pus-filled abscess. Pyomyositis is most common in tropical areas but can also occur in temperate zones.

File:CT pyomyositis.jpg

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"

File:Tropical pyomyositis CT.JPG

CT exam showing a multiloculated fluid collection in the left gluteus minimus muscle found to be a staph aureus pyomyositis in a 12-year-old healthy boy.

File:Axial T1 FS Post Gad tropical pyomyositis.JPG

Axial T1 weighted fat suppressed post IV gadolinium contrast enhanced MRI image showing a mutliloculated bacterial abscess in the left gluteal muscle which grew Staphlococcus Aureus (methicillin sensitive) thought to be due to tropical pyomyositis.

File:Cor post gad MRI Tropical pyomyositis.JPG

Coronal fat suppressed post contrast image showing a multiloculated bacterial abscess in the left gluteus minimus muscle due to tropical pyomyositis.

File:Cor T2 MRI tropical pyomyositis.JPG

Coronal T2 weighted fat suppressed image showing a multiloculated fluid collection in the left gluteal musculature due to tropical pyomositis in a 12-year-old boy.

Epidemiology

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.

Treatment

The abscesses within the muscle must be drained surgically (not all patient require surgery if there is no abscess). Antibiotics are given for a minimum of three weeks to clear the infection.