Psoas abscess

Disease Description (Causes and Symptoms)

• Definition: A psoas abscess is a condition in which pus (an abscess) accumulates within the psoas major muscle, which extends from the lumbar spine to the pelvis, or between its fascial layers.
• Pathophysiology: Infection occurs through hematogenous spread (usually primary) or direct spread from adjacent organs (such as the spine, intestines, or urinary tract) (secondary). Because the psoas muscle has an abundant blood and lymphatic supply and is adjacent to multiple organs, infection can spread to it easily.
• Main causative organisms/triggering factors:
  • Primary: Hematogenous spread—Staphylococcus aureus (especially non-tuberculous bacteria) is common. The possibility of MRSA should be considered.
  • Secondary: Direct spread from vertebral osteomyelitis, intestinal infections (cecum, small intestine, colon), urinary tract infections, pancreatic abscesses, etc.—intestinal gram-negative bacilli (e.g., E. coli), anaerobic bacteria, etc.
  • Tuberculous psoas abscess: Tuberculous spondylitis (a substantial proportion in regions with a higher prevalence of tuberculosis than developed countries).
  • Risk factors: Diabetes, history of tuberculosis, alcoholic liver disease, malignancy, immunosuppression, trauma (secondary infection after a hematoma), etc.
• Clinical symptoms:
  • Fever, chills, general malaise, weight loss, loss of appetite
  • Low back, flank, abdominal, or groin pain; a flexed-hip posture (pain is relieved when lying prone or keeping the hip slightly flexed)
  • Difficulty walking (limping); a palpable mass on the front or side of the thigh (rare)
  • Specific physical examination finding: Psoas sign—pain elicited when the hip is passively extended

Treatment Methods

• Diagnostic principles:
  • Blood tests (CBC, CRP/ESR), blood cultures (before administering antibiotics)
  • Imaging: CT (abdominopelvic CT; most useful for identifying abscesses in the pelvis and psoas region, with CT-guided drainage possible) or MRI (excellent when a spinal-associated lesion is suspected)
  • Ultrasound is accessible but has low sensitivity. Gram staining, culture, and antimicrobial susceptibility testing should be performed on specimens obtained during abscess drainage
• Antibiotic treatment:
  • Empirical antibiotics are determined according to local organism distribution and the patient's risk factors. Common choices include:
    • Broad-spectrum: vancomycin (or other MRSA coverage) + gram-negative and anaerobic coverage (e.g., cefepime or piperacillin–tazobactam)
    • Antibiotic de-escalation (targeted treatment) according to subsequent culture results
  • Treatment duration: This varies according to the causative organism and whether drainage is performed. Generally, at least several weeks after drainage (a total of 4–6 weeks or longer) is required. In tuberculous cases, standard anti-tuberculosis therapy (usually for at least 6 months) is administered.
• Drainage:
  • Percutaneous drainage (CT- or ultrasound-guided) is often recommended as the primary treatment (effective and relatively minimally invasive).
  • Surgical drainage (open or endoscopic) is necessary for complex abscesses, multiloculated/septated abscesses, cases requiring surgical treatment because of accompanying intra-abdominal lesions, or failure of percutaneous drainage.
• Concurrent treatment/management:
  • Control of underlying diseases (such as diabetes), fluid and electrolyte correction, analgesics, and other symptomatic treatment
  • Monitoring of kidney and liver function (when antibiotic dose adjustment is necessary)
  • Management of infectiousness and long-term anti-tuberculosis treatment when the cause is tuberculosis
• Precautions (during treatment):
  • Appropriate drainage and antibiotic adjustment based on culture results determine the prognosis.
  • Clinical and imaging improvement must be confirmed before discontinuing antibiotics.
  • If signs of severe sepsis appear, immediate intensive care treatment and expanded antibiotic coverage are required

Checklist Before an Outpatient Visit (Including Items to Bring and Example Questions)

• Items to bring (helpful to have):
  • A list of current medications (including prescriptions, OTC medications, and herbal medicines), and allergy history (especially medication allergies)
  • Past medical history (tuberculosis, diabetes, cancer, recent trauma or surgery, recent infections)
  • Recent test results (if available)—copies or CDs of blood tests and imaging (CT/MRI)
  • The date symptoms began and their progression (temperature changes, location and intensity of pain, walking pattern, changes in appetite and weight, etc.)
• Examples of questions frequently asked at an outpatient visit (for self-reporting):
  • When did the symptoms begin? What has the temperature been?
  • Where is the pain (back/flank/groin/thigh), and which positions worsen or relieve it?
  • Have you recently had an infection (spinal, urinary tract, or abdominal) or a history of tuberculosis?

Examples of General Questions to Ask the Doctor

• What is the expected duration of treatment with this antibiotic, and what are its common side effects?
• In my case, which option for drainage (percutaneous vs. surgical) is appropriate?
• What is the risk of recurrence after treatment, and what symptoms can be expected if it recurs?
• If my pain or fever worsens at home, when should I go to the emergency room?

Examples of Condition-Specific Questions

• I have diabetes (or an immunocompromised condition). Will the choice of antibiotics or treatment duration be different?
• If a tuberculous psoas abscess is suspected, when should anti-tuberculosis treatment be started, and what is the plan for genetic and liver function monitoring?

Additional Precautions (Summary)

• Rapid diagnosis, appropriate drainage, and antibiotic treatment based on the causative organism are important.
• In patients with diabetes or immunosuppression, or in environments with a high prevalence of tuberculosis, the possibility of a tuberculous cause must be considered.
• Immediate emergency and inpatient treatment is required in cases of high fever, impaired consciousness, rapid heart rate (suspected sepsis), or signs of failed drainage.