How to evaluate for infectious tenosynovitis?

Evaluation of Infectious Tenosynovitis

Begin with clinical assessment using Kanavel's signs for flexor tenosynovitis (fusiform finger swelling, flexed posture, pain with passive extension, tenderness along tendon sheath), then proceed immediately to ultrasound or MRI for confirmation, followed by aspiration with culture to identify the organism. 1

Initial Clinical Assessment

Key Physical Examination Findings

• For flexor tenosynovitis: Look specifically for the four Kanavel signs—these are the classic diagnostic criteria that should raise immediate suspicion 1
• For extensor tenosynovitis: Examine for dorsal hand/extremity swelling and pain, though this presents more diagnostic challenges as it lacks the classic Kanavel signs 2
• Pain disproportionate to injury near a bone or joint suggests deeper penetration and potential infectious complications 1

Critical History Elements

• Recent trauma, puncture wounds, or animal/human bites (particularly cat bites which have 75% prevalence of Pasteurella multocida) 1
• Intravenous drug use history 2
• Immunocompromised status or risk factors for atypical organisms 1

Laboratory Evaluation

Inflammatory Markers

• C-reactive protein (CRP) is the most sensitive marker with 76% sensitivity and 100% specificity for purulent flexor tenosynovitis 3
• Erythrocyte sedimentation rate (ESR) has 41% sensitivity but 100% specificity 3
• White blood cell count (WBC) has only 39% sensitivity but 100% specificity 3

Critical caveat: While elevated inflammatory markers strongly confirm infection (positive predictive value 100%), normal values cannot rule out infection due to low negative predictive values (4-13%) 3. Therefore, never rely on normal inflammatory markers to exclude the diagnosis 3.

Imaging Studies

First-Line Imaging: Ultrasound

• Ultrasound is the preferred initial imaging modality for detecting fluid within tendon sheaths, joint effusions, and abscesses 1
• Demonstrates thickened, hypoechoic tenosynovial sheath surrounding affected tendons 1, 4
• Color Doppler can assess hyperemia without IV contrast 1
• Absence of fluid essentially excludes septic tenosynovitis 1
• Ultrasound correctly diagnosed abscess in 29 of 30 patients (97% sensitivity) compared to CT's 77% sensitivity 1
• Can guide aspiration procedures for culture 1

MRI Indications

• MRI with IV contrast is superior for detecting inflammatory tenosynovitis and should be used when ultrasound is equivocal or when evaluating extent of infection 1
• Contrast-enhanced MRI increases diagnostic sensitivity for abscesses, fistulas, and extracapsular spread 1
• MRI shows lamellated hyperintense appearance of infected synovium (86-92% sensitivity, 85-87% specificity) distinct from non-infectious causes 1
• Particularly valuable for detecting bone marrow edema suggesting osteomyelitis complication 1

CT Role

• CT with IV contrast can differentiate cellulitis, myositis, tenosynovitis, and abscess 1
• Most sensitive for detecting soft tissue gas 1
• Less sensitive than MRI for early bone marrow changes but can show periosteal reaction and erosions 1

Microbiological Diagnosis

Aspiration and Culture

• Image-guided aspiration is essential as imaging alone cannot distinguish infected from non-infected fluid collections 1
• Aspiration allows organism identification which directly determines antibiotic selection 1
• Use ultrasound, CT, or fluoroscopic guidance to ensure accurate needle placement and avoid contaminating adjacent tissues 1

Expected Organisms

• Common bacterial causes: Staphylococcus aureus, Streptococcus species, Pasteurella multocida (animal bites) 1
• Atypical mycobacteria: M. marinum, M. fortuitum, M. abscessus, M. chelonae, M. bovis cause chronic granulomatous tenosynovitis, particularly in hand/wrist 1, 5
• Tissue biopsy is the most sensitive method for obtaining specimens when atypical organisms are suspected 1
• Cultures are positive in approximately 79% of surgical cases 3

Diagnostic Algorithm

1. Clinical suspicion based on Kanavel signs (flexor) or dorsal swelling/pain (extensor)
2. Obtain inflammatory markers (CRP, ESR, WBC)—if any are elevated, infection likelihood is extremely high 3
3. Perform ultrasound immediately to confirm fluid and guide aspiration 1
4. Image-guided aspiration with culture (aerobic, anaerobic, and consider mycobacterial if chronic presentation) 1
5. MRI with contrast if ultrasound equivocal, concern for deep extension, or suspicion of osteomyelitis 1
6. Tissue biopsy if cultures negative but clinical suspicion remains high, especially for atypical organisms 1, 5

Common Pitfalls

• Do not delay imaging or aspiration waiting for inflammatory markers—early diagnosis is critical to prevent complications 1
• Do not rule out infection based on normal WBC, ESR, or CRP due to poor negative predictive values 3
• Consider atypical mycobacteria in chronic, indolent cases, particularly involving hand/wrist tendons 1, 5
• Extensor tenosynovitis is easily missed due to lack of classic Kanavel signs—maintain high suspicion with dorsal extremity swelling 2
• Bilateral presentation does not exclude infection—documented cases of bilateral infectious extensor tenosynovitis exist 2