| Classification | | Myositis | Fasciitis | Non-infection (idiophatic)
• dermatomyositis
• polymyositis
• focal myositis | Without necrosis | Infection
• bacterial myositis (pyomiositis) | Necrotizing
fasciitis |
Pyomyositis
•
Rare condition
• Prevalent in tropical
countries (“tropical myositis”,
“bacterial myositis”)
•
Immunocompromised patients, i.m. drug abusers
•
Rising cases in western countries – related to HIV
•
66% - 94% different histopathological changes in muscle
•
most common MSK complication on AIDS patients
•
S pyogenes, Mycobacterium tuberculosis, M aviumintracellulare
Pyomyositis
- Role of MRI
| |
– Dif
idiophatic myositis – pyomyositis
Idiophatic myiositis is ussualy bilateral
–
Dif lymphedema – pyomyositis
Muscle
edema with no enhancement
– Dif
cellulitis – pyomyositis
Disproportional
involvement of subcutaneous tissue
–
Presence of phlegmon, abscesses
Must
be differentiated from cystic tumors, seroma, hematoma
Role
of MRI: patient‘s management
–
Clinical presentation is nonspecific
– May
be fatal if is not recognized
– One of the
few curable conditions in AIDS
MRI is the method of choice
Pyomyositis
- MR Findings
• Phlegmon with
diffuse enhancement
• Abscesses
•
Thickening of muscle fascia
• Presence of hemorhage
•
Presence of necrosis (myonecrosis) | 
 |
Pyomyositis versus Polymyositis
Pyomyositis | Idiopatic
polymyositis
|
Necrotizing
Fasciitis
• Rapidly
progressing infection (common in HIV)
•
Extensive necrosis of superficial and deep anatomical planes
•
Accompanied by severe systemic toxicity
•
Mortality rate 73%
M
Rouge, Surgery 1982
•
Indication of MRI in emergency
Necrotizing
faciitis MRI findings
•
More severe deeper involvement:
–
thickening of affected fascias
– fluid
collection along deep fascia sheet
–
extension into deep muscular septa and muscles
–
muscle necrosis
Role of MRI:
–
evaluation of the extent and depth of the process and involvement of
adjacent structures
– follow up for
assessment of late development of necrosis
M, 30 y. HIV infection, abscess of
right tight
and necrotizing fasciitis of
left distal tight. | 
 |
November 4,
2009
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