From the Guidelines
Psoas abscess is primarily caused by bacterial infection, with Staphylococcus aureus being a common pathogen, and can occur through hematogenous or lymphatic spread or direct extension from adjacent structures. The infection can lead to inflammation, tissue destruction, and pus collection within the psoas muscle compartment. According to the most recent and highest quality study 1, Staphylococcus aureus accounts for about 90% of pathogens causing pyomyositis.
Causes of Psoas Abscess
- Primary psoas abscess results from hematogenous or lymphatic spread of bacteria from distant sites
- Secondary psoas abscess develops from the direct extension of infection from adjacent structures, such as the gastrointestinal tract, urinary tract, spine, or hip joint
- Common organisms in secondary cases include E. coli, Bacteroides, Streptococcus, and Mycobacterium tuberculosis
Risk Factors
- Diabetes
- Intravenous drug use
- HIV infection
- Renal failure
- Immunocompromised state
Diagnosis and Treatment
- Diagnosis typically requires imaging (CT or MRI)
- Treatment involves appropriate antibiotics (often starting with broad-spectrum coverage like vancomycin plus piperacillin-tazobactam) for 3-4 weeks, along with drainage of the abscess either percutaneously or surgically 1.
- Addressing the underlying cause is essential for preventing recurrence, particularly in secondary cases.
Key Considerations
- Blood culture results are positive in 5%–30% of cases 1
- MRI is the imaging modality that demonstrates pyomyositis most effectively 1
- Prompt, aggressive surgical debridement is necessary to remove all necrotic tissue, sparing the deeper structures when possible 1
From the Research
Causes of Psoas Abscess
- Psoas abscess can be caused by various pathogens, including Staphylococcus aureus, Mycobacterium tuberculosis, Escherichia coli, and other enteric Gram-negative bacilli and anaerobes 2, 3, 4
- The abscess can occur due to hematogenous spread, contiguous spread from adjacent organs, trauma, or local inoculation 4
- In some cases, psoas abscess can be caused by uncommon pathogens such as Pasteurella multocida, which can infect a patient via a bite or scratch from dogs or cats 4
- Psoas abscess can also be caused by methicillin-resistant Staphylococcus aureus (MRSA), especially after spine surgery 5
- The most common accompanying disease associated with psoas abscess is diabetes mellitus, and vertebral osteomyelitis is a common underlying condition 2
Risk Factors
- Diabetes mellitus is a significant risk factor for developing psoas abscess 2
- Spine surgery, especially posterolateral fusion of the lumbar spine, can increase the risk of developing psoas abscess 5
- Trauma, bites, or scratches from animals can also increase the risk of developing psoas abscess 4