Detecting Psoas Spasm in UTI
The psoas sign should be assessed through specific physical examination maneuvers: pain with passive hip extension or pain with active hip flexion against resistance, combined with fever and localized tenderness over the psoas muscle region. 1, 2
Clinical Presentation
The classic triad for psoas involvement includes:
- Fever - typically present as a systemic inflammatory response 2
- Localized pain - in the flank, lower abdomen, or hip region that worsens with movement 2, 3
- Psoas spasm - manifesting as a limp, inability to fully extend the hip, or pain with hip movement 2, 3
Physical Examination Techniques
Psoas Sign Testing
Perform these specific maneuvers to detect psoas muscle irritation:
- Passive hip extension - With the patient lying on their side, extend the hip backward; pain indicates a positive psoas sign 1
- Active hip flexion against resistance - Ask the patient to flex the hip while you provide resistance; pain suggests psoas involvement 1
- Palpation - Deep palpation in the lower quadrant may reveal tenderness or a firm, wooden feel over the psoas region 1
Associated Findings
- Antalgic gait or limp - The patient may walk with a characteristic limp to avoid psoas muscle activation 2, 3
- Hip flexion posture - Patients often hold the hip in a flexed position to minimize psoas stretch 3
- Limited hip range of motion - Particularly with extension movements 2
Imaging Confirmation
When psoas involvement is suspected clinically:
- Ultrasound - Can demonstrate fluid collection in the psoas muscle in most cases (demonstrated in 13 of 16 patients in one series) 2
- CT scan with contrast - Gold standard for confirming psoas abscess, showing either fluid collection or presuppurative changes 2, 4
- MRI - Can be used but is not routinely necessary for diagnosis 2
Critical Context for UTI-Associated Cases
Psoas abscess secondary to UTI is uncommon but important to recognize. 4, 5 When UTI is the suspected source:
- The infection typically spreads from pyelonephritis or perinephric infection to the adjacent psoas muscle 4, 6
- E. coli is the most common organism in UTI-related psoas abscesses 2, 4, 6
- Emphysematous UTI can rarely extend to cause psoas involvement 6
Laboratory Findings
Supporting laboratory evidence includes:
- Elevated inflammatory markers - C-reactive protein and erythrocyte sedimentation rate 2
- Leukocytosis - High neutrophil count may be present 2
- Urinalysis abnormalities - Pyuria, bacteriuria if UTI is the source 4, 5
Important Pitfall
Avoid aggressive rectal examination when psoas abscess is suspected, as this can rupture the abscess and cause peritonitis. 3 The diagnosis should rely primarily on the psoas sign, imaging, and less invasive examination techniques.