BRUCELLOSIS OF THE SPINE
Endemic Zoonosis | Spondylodiscitis | Prolonged Antibiotic Therapy
BRUCELLA SPECIES
Critical Must-Knows
- Endemic regions: Mediterranean, Middle East, Central Asia, Latin America
- Transmission: Unpasteurized dairy products, direct animal contact
- Lumbar spine most commonly affected (L4-L5 typical)
- Pedro Pons sign: Erosion of anterosuperior vertebral corner on X-ray
- Paraspinal abscess less common than tuberculosis (TB)
- Diagnosis: Serology (Rose Bengal, SAT) and blood cultures
- Treatment: Prolonged combination antibiotics for 3 to 6 months
Examiner's Pearls
- "Pedro Pons sign distinguishes early brucellosis from TB
- "Disc space preserved early - unlike pyogenic infection
- "B. melitensis is the most pathogenic species for humans
- "Surgery rarely needed except for neurological deficit or instability
Clinical Imaging
Imaging Gallery
Critical Spinal Brucellosis Exam Points
Geographic Clues
Endemic regions: Mediterranean (Spain, Italy, Greece), Middle East, Central Asia, Latin America. Travel history is essential in non-endemic countries like Australia. Ask about dairy consumption and animal contact.
Pedro Pons Sign
Pathognomonic radiographic finding: Erosion of the anterosuperior vertebral corner. Occurs early in disease before disc space narrowing. Helps differentiate from TB (which affects anterior vertebral body more diffusely).
Serological Diagnosis
Rose Bengal test: Rapid screening (agglutination). Standard Agglutination Test (SAT): Titres greater than 1:160 diagnostic. Blood cultures: Positive in 50-70% of acute cases. Require prolonged incubation.
Antibiotic Regimen
First-line: Doxycycline 100mg BD plus rifampicin 600-900mg daily for 3 to 6 months. Alternative: Doxycycline plus streptomycin/gentamicin. Monotherapy has high relapse rates (10-40%).
Brucellosis vs Tuberculosis Spondylitis
| Feature | Brucellosis | TB Spondylitis (Pott's Disease) |
|---|---|---|
| Endemic region | Mediterranean, Middle East, Latin America | Worldwide, especially developing countries |
| Transmission | Zoonosis (dairy, animal contact) | Respiratory (Mycobacterium tuberculosis) |
| Spine level | Lumbar most common (L4-L5) | Thoracolumbar junction (T10-L2) |
| Pathognomonic sign | Pedro Pons sign (anterosuperior erosion) | Gibbus deformity, vertebra plana |
| Paraspinal abscess | Less common (20-30%) | Common (50-75%), cold abscess |
| Disc involvement | Preserved early, involved late | Early disc destruction common |
| Diagnosis | Serology (SAT greater than 1:160), blood culture | Tissue biopsy, PCR, culture (slow) |
| Treatment duration | 3 to 6 months antibiotics | 9 to 12 months anti-TB therapy |
| Surgery need | Rarely needed (less than 10%) | More often needed (20-30%) |
MASBrucella Species
Memory Hook:MAS - Melitensis is Most pathogenic, Abortus from bovines, Suis from Swine
DAIRYTransmission Routes
Memory Hook:DAIRY reminds you that unpasteurized dairy products are the most common transmission route!
DRAntibiotic Regimen
Memory Hook:DR for 3-6 months - Doctor prescribes Doxycycline plus Rifampicin for Months!
CORNERPedro Pons Sign
Memory Hook:CORNER erosion at the anterosuperior corner - think Pedro Pons pointing to the corner!
Overview and Epidemiology
Spinal brucellosis is the most common form of osteoarticular brucellosis, a zoonotic infection caused by Brucella species. It represents one of the most important causes of spondylodiscitis in endemic regions.
Causative organisms:
- Brucella melitensis (goats/sheep): Most common and most virulent for humans (responsible for greater than 90% of spinal cases)
- Brucella abortus (cattle): Milder disease
- Brucella suis (pigs): Variable severity
- Brucella canis (dogs): Rare cause of human disease
Epidemiology:
- Endemic in Mediterranean basin, Middle East, Indian subcontinent, Central Asia, Latin America
- 500,000 new cases annually worldwide
- Osteoarticular involvement: 6-12% of all brucellosis cases
- Spondylitis: Most common osteoarticular manifestation (50-60% of skeletal brucellosis)
- Males affected more than females (2:1)
- Peak incidence: 40-60 years (spinal involvement)
Endemic Regions
The MMCL regions are highest risk: Mediterranean, Middle East, Central Asia, and Latin America. In non-endemic countries like Australia, always ask about travel and dietary history.
Pathophysiology
Brucella characteristics:
- Small, gram-negative coccobacillus
- Facultative intracellular organism (survives within macrophages)
- Slow-growing (cultures need 4-6 weeks incubation)
- Non-motile, non-spore forming
- No exotoxins or plasmids
Transmission routes:
- Ingestion: Unpasteurized milk, cheese, ice cream (most common)
- Direct contact: Through skin abrasions with infected animals/products
- Inhalation: Aerosols in laboratories, abattoirs, farms
- Rarely: Vertical transmission, sexual transmission
Occupational Risk Groups
High-risk occupations: Veterinarians, farmers, shepherds, abattoir workers, laboratory personnel. Always ask about occupation in patients from endemic areas presenting with back pain and fever.
Pathophysiology of spinal involvement:
- Hematogenous spread from primary infection (usually intestinal)
- Brucellae lodge in vertebral metaphyseal vessels
- Initial osteomyelitis of vertebral endplate
- Spread to adjacent disc and vertebra (spondylodiscitis)
- Granulomatous inflammation with microabscess formation
- Less destruction than pyogenic infection due to granulomatous nature
Predilection for lumbar spine:
- L4-L5 most commonly affected (40-50%)
- L3-L4 second most common
- Lumbar spine involved in 70-80% of cases overall
- Cervical spine rare (less than 5%)
- Multifocal involvement in 10-20%
Why Lumbar Spine?
The lumbar spine is most affected because of the rich blood supply and large vertebral body size at L4-L5, providing more area for bacterial seeding from the bloodstream.
Clinical Presentation
Systemic symptoms:
- Undulant fever (classically rises and falls - "Malta fever")
- Night sweats, malaise, fatigue
- Weight loss, anorexia
- Hepatosplenomegaly (30-50%)
- May have subacute or chronic presentation
Spinal symptoms:
- Back pain: Insidious onset, progressive, worse at night
- Localized tenderness: Over affected vertebrae
- Muscle spasm: Paravertebral muscle guarding
- Reduced range of motion: Particularly extension
Neurological Involvement
- Occurs in 10-20% of spinal brucellosis
- Radiculopathy most common (root compression)
- Epidural abscess can cause cord compression
- Cauda equina syndrome rare but serious
- Better prognosis than TB myelopathy
Differential Symptoms
- More indolent than pyogenic spondylodiscitis
- Less kyphotic deformity than TB
- Fever less prominent than pyogenic infection
- Systemic symptoms more prominent than TB
- May have concurrent sacroiliitis (20-30%)
Key clinical features distinguishing from TB:
- More indolent course with systemic symptoms
- Less severe destruction and deformity
- Paraspinal abscess less common and smaller
- Neurological involvement less severe
- Better response to medical treatment
Sacroiliac Involvement
Concurrent sacroiliitis occurs in 20-30% of spinal brucellosis and can cause buttock pain, positive FABER test, and SI joint tenderness. This combination (spine + SI joint) should raise suspicion for brucellosis in endemic regions.
Investigations
Serological Tests
| Test | Method | Interpretation |
|---|---|---|
| Rose Bengal Test | Rapid agglutination screening | Highly sensitive (greater than 95%), confirm positive with SAT |
| Standard Agglutination Test (SAT) | Quantitative antibody titre | Greater than 1:160 diagnostic; greater than 1:320 highly suggestive |
| 2-Mercaptoethanol (2-ME) Test | Detects IgG (active infection) | Positive suggests active disease, useful for monitoring treatment |
| Coombs Test | Detects blocking antibodies | Useful for chronic brucellosis with negative SAT |
| ELISA | IgM and IgG antibodies | High sensitivity, useful for monitoring response |
Blood Cultures
- Positive in 50-70% of acute cases
- Require prolonged incubation (up to 4-6 weeks)
- Alert laboratory to clinical suspicion (biosafety precautions needed)
- Modern BACTEC systems improve yield
Other Laboratory Findings
- CRP elevated (usually less than pyogenic infection)
- ESR elevated (50-100mm/hr typical)
- Mild normocytic anaemia
- Leukopenia or normal WCC (unlike pyogenic infection)
- Elevated liver enzymes (50%)
Laboratory findings show inflammatory markers with serology confirming diagnosis in most cases.
Imaging Gallery
Management
Principles of Treatment
- Combination therapy is mandatory (monotherapy has 10-40% relapse)
- Prolonged duration: Minimum 3 months, typically 6 months for spondylitis
- Intracellular penetration: Brucella survives in macrophages
- Good bone penetration required
First-Line Regimens
Antibiotic Regimens for Spinal Brucellosis
| Regimen | Drugs | Duration | Notes |
|---|---|---|---|
| WHO Recommended | Doxycycline 100mg BD + Rifampicin 600-900mg OD | 3-6 months | Oral regimen, best compliance |
| Alternative (more efficacious) | Doxycycline 100mg BD + Streptomycin 1g IM OD | 6 weeks strep, 6 months doxy | Higher cure rate but injectable |
| Severe disease | Doxycycline + Rifampicin + Gentamicin | 2-3 weeks gent, then oral | For neurological involvement |
| Pregnancy | Rifampicin + TMP-SMX | Throughout pregnancy | Avoid doxycycline and aminoglycosides |
Treatment Monitoring
- Clinical response: Fever resolution in 1-2 weeks
- CRP/ESR: Should decrease by 2-4 weeks
- Serology: SAT may remain positive, 2-ME should become negative
- MRI: Repeat at 3-6 months if response uncertain
Treatment Duration
Minimum 3 months, but most experts recommend 6 months for spondylodiscitis. Shorter courses have unacceptable relapse rates (up to 30%). Continue until clinical cure and normalization of inflammatory markers.
Complications
Treatment outcomes:
- Cure rate: 95% with appropriate antibiotics
- Relapse rate: 5-10% with adequate treatment (higher with monotherapy)
- Time to response: 2-4 weeks for symptom improvement
- Residual back pain: 20-30% have some long-term pain
Complications:
Complications of Spinal Brucellosis
| Complication | Incidence | Management |
|---|---|---|
| Neurological deficit | 10-20% | Urgent decompression if progressive |
| Epidural abscess | 10-20% | Surgery if not responding to antibiotics |
| Paraspinal abscess | 20-30% | Usually responds to antibiotics, drain if large |
| Relapse | 5-10% | Retreatment with prolonged course |
| Chronic pain | 20-30% | Multidisciplinary pain management |
| Instability | Rare (less than 5%) | Surgical stabilization |
Prognostic factors:
- Early diagnosis improves outcomes
- Neurological involvement worsens prognosis
- Treatment delay associated with higher complication rate
- Compliance with prolonged antibiotics crucial
Evidence Base
Treatment Duration for Brucellar Spondylitis
- Retrospective study of 219 patients with brucellar spondylitis
- Treatment duration less than 3 months associated with 30% relapse rate
- Treatment for 3-6 months reduced relapse to less than 10%
- Doxycycline plus streptomycin showed lower relapse than doxycycline plus rifampicin
MRI Features of Spinal Brucellosis
- MRI sensitivity greater than 95% for spinal brucellosis
- Disc involvement in 87% of cases
- Paraspinal soft tissue involvement in 31%
- Epidural involvement in 24%
WHO Recommended Treatment
- Doxycycline plus rifampicin for 6 weeks is standard for uncomplicated brucellosis
- Osteoarticular disease requires extended treatment (minimum 12 weeks)
- Aminoglycoside-containing regimens may be more effective but less practical
- Combination therapy essential to prevent relapse
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Endemic Region Travel History
"A 55-year-old man presents with 6 weeks of progressive low back pain, night sweats, and weight loss. He returned from a trip to Turkey 3 months ago where he consumed unpasteurized cheese. Examination reveals lumbar tenderness at L4-5 with restricted range of motion. How would you approach this case?"
Scenario 2: Differentiating from TB Spondylitis
"A 45-year-old woman from rural Pakistan presents with 3 months of progressive thoracolumbar back pain. MRI shows spondylodiscitis at L1-L2 with a small paraspinal collection. How do you differentiate between TB spondylitis and brucellosis, and how does this affect your management?"
Scenario 3: Neurological Deterioration on Treatment
"A 50-year-old man with confirmed spinal brucellosis (L4-L5) has been on doxycycline and rifampicin for 4 weeks. He now presents with progressive bilateral lower limb weakness (power 3/5), urinary retention, and reduced perineal sensation. MRI shows enlarging epidural abscess with cord compression. What is your management?"
Australian Context
Epidemiology in Australia:
Spinal brucellosis is rare in Australia as the country has been officially brucellosis-free for livestock since 1989. Cases that occur in Australia are virtually always imported from endemic regions. Clinicians should maintain a high index of suspicion in patients with:
- Recent travel to endemic regions (Mediterranean, Middle East, Central Asia, Latin America)
- Immigration from endemic countries
- Consumption of unpasteurized dairy products overseas
- Occupational exposure overseas (veterinarians, farmers working abroad)
Diagnostic considerations:
Australian laboratories may have limited experience with Brucella cultures, which require prolonged incubation and biosafety level 3 precautions. When brucellosis is suspected, it is essential to alert the laboratory to ensure appropriate handling and extended culture times. Serology (Rose Bengal and SAT) is available through reference laboratories and remains the primary diagnostic modality. PCR testing is increasingly available for tissue specimens.
Management in Australian practice:
The antibiotic regimens remain the same as international guidelines: doxycycline plus rifampicin for 3-6 months. Rifampicin is available on the PBS for this indication. Patients may require specialist infectious diseases consultation given the rarity of the condition and the prolonged treatment course required. Surgical intervention, when needed, follows standard spine surgery principles with post-operative continuation of antibiotics for the full 6-month duration.
BRUCELLOSIS OF THE SPINE
High-Yield Exam Summary
Epidemiology
- •Endemic: Mediterranean, Middle East, Central Asia, Latin America
- •Transmission: Unpasteurized dairy (most common), animal contact
- •B. melitensis is most common and virulent species
- •Spondylodiscitis in 6-12% of brucellosis cases
Clinical Features
- •Lumbar spine most common (L4-L5)
- •Insidious back pain with systemic symptoms
- •Undulant fever, night sweats, weight loss
- •Less destruction than TB, smaller abscesses
Diagnosis
- •Rose Bengal: Screening (greater than 95% sensitive)
- •SAT greater than 1:160: Diagnostic
- •Blood cultures: Positive 50-70%, need prolonged incubation
- •Pedro Pons sign: Anterosuperior vertebral corner erosion
Imaging
- •X-ray: Pedro Pons sign early, disc narrowing late
- •MRI: T2 high signal, enhancement, epidural collection
- •Less destruction and smaller abscesses than TB
- •Disc preserved early (unlike pyogenic infection)
Treatment
- •First-line: Doxycycline 100mg BD + Rifampicin 600-900mg OD
- •Duration: 3-6 months (minimum 3 months)
- •Alternative: Doxycycline + Streptomycin (more effective but injectable)
- •Surgery rare (less than 10-15%): neurological deficit, large abscess, instability
Key Differences from TB
- •Brucellosis: Lumbar spine, less destruction, smaller abscesses
- •TB: Thoracolumbar, gibbus, large cold abscesses
- •Brucellosis: Serology diagnosis; TB: Tissue diagnosis
- •Brucellosis: 3-6 months treatment; TB: 9-12 months