Psoas abscess

OVERVIEW

• Psoas abscess is a suppurative collection in the psoas muscle
• It is commonly missed or diagnosed late, with potential for severe morbidity
• The psoas muscle extends through the retroperitoneal space from the lateral borders of T12 to L5 and inserts on the lesser trochanter of the femur (30% have an additional psoas minor muscle anterior to the psoas major).

PATHOPHYSIOLOGY

Psoas abscess may be primary in origin (see risk factors) or secondary, due to local spread from:

• Vertebral osteomyelitis
• Inflammatory bowel disease (especially Crohn’s disease)
• Pyelonephritis

Complications

• Septicaemia and septic shock
• Osteomyelitis
• Epidural abscess
• Pyelonephritis

CAUSE

Causative organisms include:

• staphylococcus spp (most common)
• Streptococci
• Gram negative enteric bacteria
• Tuberculosis (immunosuppressed, or in endemic areas)

RISK FACTORS

Risk factors for primary psoas abscess include:

• Underlying immunosuppression (e.g DM, HIV, malignancy)
• IVDU
• Tuberculosis
• Local recent surgery or trauma
• Infected psoas hematoma
• Psoas haematoma may occur in haemophiliac patients

CLINICAL FEATURES

History

• may be non-specific initially
• increasing pain, usually over several days, affecting the back, buttock, groin or hip
• pain may radiate to the hip and thigh (L-2,3,4 dermatome)
• risk factors may be present
• suspect if no clear history of any trauma or other musculoskeletal injury

Examination

• fever may be present
• point tenderness of the back (may be absent or diffuse early in the presentation)
• evidence of psoas irritation
  • position of comfort is the supine position, with the knee moderately flexed and the hip mildly externally rotated
  • hip pain with movement (especially resisted hip flexion) or weight bearing

INVESTIGATIONS

Bedside

• glucose (diabetes mellitus)

Laboratory

• FBC (leukocytosis)
• CRP
• UEC
• Septic screen including blood cultures and urine MCS (exclude UTI)

Imaging

• CT abdomen may diagnose psoas abscess, and may exclude alternate diagnoses
• MRI is the gold standard, it is more sensitive than CT abdomen and can also diagnoses/ exclude epidural abscess
• ultrasound and radiographs are not useful (a scoliosis due to muscle spasm, concave to the affected side, may be present)

MANAGEMENT

Resuscitation

• rarely required

Specific therapy

• empiric antibiotics: flucloxacillin or vancomycin
• treat tuberculosis if required
• consider CT-guided drainage
• surgical drainage if CT-guided drainage is not possible or fails (~10% of cases)

Supportive care and monitoring

References and links

Journal articles

• van den Berge M, de Marie S, Kuipers T, Jansz AR, Bravenboer B. Psoas abscess: report of a series and review of the literature. Neth J Med. 2005 Nov;63(10):413-6 PMID: 16301764.
• Wong OF, Ho PL, Lam SK. Retrospective review of clinical presentations, microbiology, and outcomes of patients with psoas abscess. Hong Kong Med J. 2013 Oct;19(5):416-23. PMID: 23603777.
• Yacoub WN, Sohn HJ, Chan S, Petrosyan M, Vermaire HM, Kelso RL, Towfigh S, Mason RJ. Psoas abscess rarely requires surgical intervention. Am J Surg. 2008 Aug;196(2):223-7. PMID: 18466865.