Spinal Infections — Pyogenic vs TB

Spinal infections encompass a spectrum of conditions including pyogenic vertebral osteomyelitis (PVO), discitis, epidural abscess, and tuberculous spondylitis (Pott disease). Early diagnosis and appropriate treatment are essential to prevent neurological deterioration, spinal instability, and sepsis. The distinction between pyogenic and tuberculous aetiology determines the treatment strategy, duration of antibiotic therapy, and surgical approach.

• Incidence of pyogenic vertebral osteomyelitis: approximately 2–5 per 100,000 population; increasing due to ageing population, immunosuppressive therapies, IV drug use, and spinal instrumentation
• Most common spinal level: lumbar spine (45–50%), followed by thoracic (35%), and cervical (15%); cervical infection carries highest risk of neurological compromise
• Pott disease (spinal TB): accounts for approximately 50% of skeletal TB worldwide; most common cause of spinal infection in TB-endemic regions; thoracolumbar junction most commonly affected
• Spinal infection must always be considered in any patient with back pain + fever + elevated inflammatory markers — early MRI is the investigation of choice; delay in diagnosis averages 3–6 months in many series, leading to preventable neurological injury

• Symptoms: severe localised back pain; point tenderness; fever; malaise; radicular pain if nerve root compression; myelopathy if cord compression
• Risk factors: diabetes, IV drug use, immunosuppression, recent urological or dental procedure, IV catheter, skin infection — haematogenous seeding from distant source is the most common route
• MRI spine with gadolinium: investigation of choice — disc signal change (T2 hyperintensity), end-plate erosion, paravertebral and epidural soft tissue enhancement, epidural abscess; MRI identifies early infection before X-ray changes develop; X-ray changes (disc space narrowing, end-plate erosion) take 3–6 weeks to appear
• Blood cultures: positive in approximately 50–60%; collect before antibiotics whenever possible; repeat if initial cultures negative
• CT-guided biopsy: performed when blood cultures negative or to confirm organism and sensitivities; diagnostic yield approximately 50–75%; send for standard culture, AFB, TB PCR, and histology; hold antibiotics for 48–72 hours before biopsy if patient stable to improve yield
• Nuclear medicine (bone scan, PET): useful when MRI equivocal or contraindicated; high sensitivity for infection but low specificity

• Radiological features: anterior vertebral body destruction; relative disc preservation until late; loss of anterior vertebral height → angular kyphosis; subligamentous spread producing multilevel involvement; calcified paraspinal abscess in chronic cases
• Gibbus deformity: severe angular kyphosis from anterior vertebral collapse in Pott disease — may develop acutely with vertebral body fracture, or gradually from progressive anterior column destruction; associated with paraplegia of Pott (compressive myelopathy from abscess, granulation tissue, or kyphosis)
• Psoas abscess: TB pus tracking along the psoas sheath from the lumbar spine to the iliac fossa or groin; presents as fluctuant groin swelling or iliopsoas spasm causing hip held in flexion; CT demonstrates paraspinal extension
• Neurological involvement: approximately 30–40% of Pott disease patients develop neurological deficit; caused by direct cord compression (abscess, granulation tissue, sequestrum) or ischaemia from vascular involvement; early surgery improves neurological outcome
• MRI TB spine: anterior column predominantly affected; multilevel disease in approximately 20%; skip lesions; subligamentous spread; cold abscess tracking; relative disc preservation early — distinguishes from pyogenic where disc is destroyed early

• Pyogenic: IV antibiotics guided by culture and sensitivity; empirical therapy with flucloxacillin (or vancomycin for MRSA risk) ± gentamicin for Gram-negative cover; minimum 6 weeks of IV antibiotics followed by oral step-down; total duration typically 3–6 months; monitor ESR, CRP, and MRI for treatment response
• IV to oral switch for pyogenic: once clinical improvement, CRP trending down, and sensitivities confirm an appropriate oral agent — oral high-bioavailability agents (rifampicin + ciprofloxacin for S. aureus; fluoroquinolone for Gram-negatives) are effective; early oral switch supported by recent OVIVA trial data
• OVIVA trial (2019): oral vs IV antibiotics in bone and joint infections — non-inferiority demonstrated for oral high-bioavailability antibiotics; oral step-down after initial IV induction now standard in many centres for pyogenic spinal infections without epidural abscess requiring urgent drainage
• TB spondylitis: standard RIPE regimen — rifampicin, isoniazid, pyrazinamide, ethambutol × 2 months; then rifampicin + isoniazid × 10 months; total 12 months for spinal TB (longer than peripheral joint TB due to spinal cord risk)
• Bracing: thoracolumbar orthosis (TLSO) for pain relief and spinal stabilisation during medical treatment; does not substitute for surgical fixation when instability is present

• Titanium implants in active TB and pyogenic infection: modern evidence supports use of titanium instrumentation even in active infection — titanium resists biofilm more than stainless steel; debridement + instrumented fusion in a single stage is now accepted; historically feared but now well-evidenced to be safe when combined with appropriate antibiotic/anti-TB therapy
• Hong Kong procedure: anterior radical debridement + interbody strut bone graft for Pott disease; classic approach for anterior column reconstruction; augmented with posterior instrumentation in modern practice

• Paraplegia of Pott: neurological deficit from TB spondylitis; two mechanisms — (1) active disease with cord compression from abscess/granulation tissue/sequestrum (responds well to surgical decompression and anti-TB therapy); (2) healed disease with fixed kyphosis compressing cord over the apex of the gibbus (late-onset Pott paraplegia — requires osteotomy and cord decompression, more complex); distinguishing active from healed disease on MRI guides management
• Brucella spondylitis: important differential in Middle East, Mediterranean, and livestock-farming regions; Brucella melitensis or B. abortus; insidious onset similar to TB but Rose Bengal agglutination test and Brucella serology positive; CT-guided biopsy confirms; treated with doxycycline + rifampicin for 3–6 months; surgical indications similar to pyogenic spondylitis
• Post-operative spinal infection: iatrogenic spinal infection after instrumented surgery; presents weeks to months post-operatively; Gram-positive organisms (S. aureus, S. epidermidis) predominate; early infections — debridement, irrigation, and implant retention if fusion not yet achieved; late infections — implant removal once fusion confirmed; Propionibacterium acnes (Cutibacterium acnes) common in cervical spine post-op
• IGRA in TB spondylitis: QuantiFERON Gold has high sensitivity but cannot distinguish active from latent TB; use alongside clinical, radiological, and microbiological data; cannot be used alone to initiate anti-TB treatment

• MRI spine: investigation of choice for spinal infection — identifies infection before X-ray changes; X-ray changes take 3–6 weeks to appear
• Pyogenic: S. aureus most common; disc destroyed early; epidural abscess (warm); acute onset
• TB spondylitis: disc relatively spared initially; anterior vertebral body destruction; cold abscess; psoas abscess; subligamentous spread; insidious onset
• Gibbus deformity: angular kyphosis from anterior collapse in Pott disease; associated with Pott paraplegia
• Pyogenic antibiotics: 6 weeks IV then oral step-down; 3–6 months total; OVIVA trial supports oral high-bioavailability agents
• Spinal TB: RIPE × 2 months intensive + RI × 10 months = 12 months total for spinal TB
• Epidural abscess + neurological deficit: surgical emergency — decompress urgently; outcome time-dependent
• Titanium instrumentation: safe in active infection and TB; single-stage debridement + fusion acceptable
• Pott paraplegia: active = decompression + anti-TB therapy responds well; late (fixed kyphosis) = complex osteotomy required
• Hold antibiotics 48–72 hours before CT-guided biopsy to improve culture yield