What is discitis osteomyelitis?

Discitis Osteomyelitis: Definition, Diagnosis, and Management

Discitis osteomyelitis is an infection of the intervertebral disc and adjacent vertebral bodies, often resulting from hematogenous seeding from a distant focus, with potential extension to paravertebral and epidural soft tissues. 1

Epidemiology and Pathophysiology

• Native vertebral osteomyelitis (NVO) occurs most commonly through hematogenous seeding of the adjacent disc space from a distant infectious focus, as the disc itself is avascular 1
• The incidence is approximately 2.4 cases per 100,000 annually, increasing with age to over 6/100,000 in adults over 70 years 2
• Approximately 80% of cases are hematogenous in origin, while 20% develop after spinal surgery 2
• The infection typically begins with a septic embolus to the vertebral endplate, then spreads to the adjacent disc 1

Clinical Presentation

• Recalcitrant back or neck pain unresponsive to conservative measures is the most common presenting symptom 1
• Fever may or may not be present 1
• Elevated inflammatory markers (ESR, CRP) are typically present 1
• Neurologic symptoms may occur if there is extension to the epidural space 1
• Diagnosis is often delayed by several months and initially misdiagnosed as a degenerative process 1

Risk Factors

• Recent bloodstream infection, particularly Staphylococcus aureus 1
• Infective endocarditis 1
• Immunocompromised state 1
• Advanced age 1
• Intravenous drug use 1, 3
• Diabetes, long-term steroid use, liver failure, and renal failure 1
• Recent spinal procedures or surgery 3

Diagnostic Approach

Clinical Suspicion

• Suspect discitis osteomyelitis in patients with:
  • New or worsening back/neck pain with fever 1
  • New or worsening back/neck pain with elevated ESR or CRP 1
  • New or worsening back/neck pain with recent bloodstream infection or endocarditis 1
  • Fever with new neurologic symptoms with or without back pain 1

Imaging

• MRI is the imaging modality of choice (sensitivity 97%, specificity 93%, accuracy 94%) 1
  • Characteristic findings include inability to distinguish margins between disc space and adjacent vertebral marrow on T1-weighted images, with increased signal intensity on T2-weighted images 1
  • Gadolinium enhancement may be the first sign of acute inflammation 1
• If MRI is contraindicated (implantable devices, claustrophobia):
  • Consider combination spine gallium/Tc99 bone scan, CT scan, or PET scan 1
• Plain radiographs have limited sensitivity in early disease 1
• CT is superior to radiographs for detecting early bone changes, with abnormalities visible in nearly half of patients within the first 2 weeks 1

Microbiologic Diagnosis

• Blood cultures should be obtained in all patients 1
• Image-guided aspiration biopsy is recommended in patients with suspected discitis osteomyelitis 1
• If paravertebral fluid collections are present, CT-guided aspiration should be performed 3
• The yield of CT-guided percutaneous sampling is 31-91% 3
• Consider withholding antibiotics for 1-2 weeks before biopsy if clinically feasible 3
• If initial biopsy is negative, consider repeat biopsy after 72 hours 3
• In patients with S. aureus bloodstream infection within the preceding 3 months and compatible MRI findings, disc space aspiration may not be necessary 1

Microbiology

• Discitis osteomyelitis is commonly monomicrobial 1
• Staphylococcus aureus is the most frequent causative organism (40-60%) 1, 2
• Tuberculosis accounts for approximately 20% of cases 2
• Consider Brucella species in patients from endemic areas 1
• Consider fungal pathogens in immunocompromised hosts 1

Treatment

Antimicrobial Therapy

• Definitive therapy should be based on culture results and susceptibility testing 1
• Antibiotic therapy for 4-8 weeks appears to provide the optimal balance of efficacy and treatment duration for most patients with discitis osteomyelitis 4
• Empiric antibiotics should be withheld until microbiologic diagnosis is established, except in patients with:
  • Hemodynamic instability
  • Sepsis or septic shock
  • Progressive or severe neurologic symptoms 1

Surgical Intervention

• Surgical intervention is indicated for:
  • Progressive neurologic deficits
  • Progressive deformity
  • Spinal instability with or without pain despite adequate antimicrobial therapy 1
• Consider surgical debridement with or without stabilization for:
  • Persistent or recurrent bloodstream infection without alternative source
  • Worsening pain despite appropriate medical therapy 1
• Surgery is generally not recommended when bony imaging findings worsen at 4-6 weeks if clinical symptoms, physical examination, and inflammatory markers are improving 1

Monitoring Response to Treatment

• Monitor systemic inflammatory markers (ESR and/or CRP) after approximately 4 weeks of antimicrobial therapy 1
• ESR values >50 mm/hour and CRP values >2.75 mg/dL after 4 weeks of treatment may indicate higher risk of treatment failure 1
• Routine follow-up MRI is not recommended in patients with favorable clinical and laboratory response 1
• Consider follow-up MRI to assess evolutionary changes in epidural and paraspinal soft tissues in patients with poor clinical response 1
• Improvement in paravertebral and epidural soft tissue on follow-up MRI correlates best with clinical improvement 1

Differential Diagnosis

• Non-infectious processes can mimic infectious discitis/osteomyelitis:
  • Pseudarthrosis in ankylosing spondylitis
  • Amyloidosis
  • Destructive spondyloarthropathy of hemodialysis
  • Modic changes type 1
  • Neuropathic arthropathy
  • Calcium pyrophosphate dehydrate spondyloarthropathy
  • Gout 5

Prognosis

• Mortality rates have improved from approximately 25% in the pre-antibiotic era to 0-11% in contemporary cohorts 1
• Factors associated with worse outcomes may include:
  • Multidisc disease
  • Concomitant epidural abscess
  • Lack of surgical therapy when indicated
  • Infection with S. aureus
  • Advanced age
  • Significant comorbidities 1