What are the diagnostic tests and treatment options for Brucella sacroileitis?

Diagnostic Confirmation of Brucella Sacroiliitis

In endemic areas, confirm Brucella sacroiliitis with blood cultures (2 sets), Brucella serology (titers ≥1:160), and MRI of the spine—image-guided biopsy is NOT needed if blood cultures are positive or serology is strongly positive (≥1:160). 1, 2

Diagnostic Algorithm

Step 1: Obtain Blood Cultures and Serology

• Draw 2 sets of aerobic and anaerobic blood cultures in all patients with suspected Brucella sacroiliitis before starting antibiotics 1, 2, 3
• Alert the laboratory beforehand as Brucella requires biosafety level 3 precautions due to aerosolized transmission risk to laboratory workers 2
• Blood cultures have 15-70% sensitivity depending on laboratory practices and require prolonged incubation up to 4 weeks 2, 4
• Obtain Brucella serology using standard tube agglutination (STA) test—titers ≥1:160 are diagnostic when combined with compatible clinical presentation 1, 2, 3
• In endemic settings, false-negative serology is unusual; all patients with brucellar vertebral osteomyelitis had titers ≥1:160 in published series 1

Step 2: Perform MRI Imaging

• MRI of the spine is the imaging modality of choice with 97% sensitivity and 93% specificity for Brucella sacroiliitis and spondylitis 2, 3
• MRI demonstrates inflammatory changes in vertebral bodies, disc involvement, and paravertebral/epidural abscesses 1
• Obtain baseline ESR and CRP as inflammatory markers are typically elevated 1, 2

Step 3: Determine Need for Biopsy

Do NOT perform image-guided aspiration biopsy if: 1, 2, 3

• Blood cultures are positive for Brucella species
• Brucella serology is strongly positive (≥1:160) in endemic settings
• Both clinical presentation and imaging are compatible with Brucella infection

Consider image-guided biopsy only if: 1

• You are in a non-endemic area (like the United States) where false-positive serology is more likely
• Blood cultures are negative AND serology is negative or equivocal despite high clinical suspicion
• Alternative diagnoses need to be excluded

Step 4: Consider Bone Marrow Culture

• Bone marrow culture has the highest sensitivity and should be reserved for cases where blood cultures are negative despite high clinical suspicion 2
• Bone marrow is the investigation of choice when blood cultures fail to yield organisms 2

Clinical Context to Recognize

Look for these specific features that suggest Brucella sacroiliitis: 2, 3, 5

• Subacute presentation with low-grade relapsing fever and afternoon temperature swings with profuse sweating
• Severe back pain or sciatica radiculopathy, particularly affecting the lumbar spine (L4-L5 levels most common)
• Epidemiologic risk factors: consumption of unpasteurized dairy products, occupational exposure to livestock, or residence in endemic areas
• Osteoarticular involvement is the most common complication of brucellosis (prevalence 2-77%) 3, 5

Critical Pitfalls to Avoid

• Do not wait for antibody test results before starting treatment if clinical suspicion is high and imaging is compatible 2
• Do not perform unnecessary biopsies in endemic settings with positive blood cultures or strongly positive serology (≥1:160), as this exposes patients to procedural risks without added diagnostic value 1
• In non-endemic areas like the United States, be aware that false-positive serology is more common, and biopsy may be warranted even with positive serology 1
• Brucella spondylitis is commonly mistaken for tuberculous spondylitis, leading to delayed diagnosis and inappropriate treatment 6
• Normal CSF protein levels do not rule out neurobrucellosis if it develops 1

Treatment Considerations After Diagnosis

Once confirmed, treat with doxycycline 100 mg twice daily for 6 weeks PLUS either streptomycin 15 mg/kg IM daily for 2-3 weeks OR gentamicin 5 mg/kg IV daily for 7 days 2, 3

• Aminoglycoside-containing regimens may be superior for brucellar spondylitis compared to rifampicin-containing regimens 2
• Immobilization is crucial for cervical involvement to prevent devastating neurological complications 2
• Consult infectious disease specialist and spine surgeon, especially in non-endemic areas 1