What is a spinal epidural abscess?

Spinal Epidural Abscess: Definition, Diagnosis, and Management

A spinal epidural abscess (SEA) is a suppurative infection and infectious disease emergency that forms in the epidural space of the spine, causing potential neurological damage through direct compression of the spinal cord or by vascular compromise, leading to significant morbidity and mortality if not promptly diagnosed and treated. 1

Epidemiology and Pathogenesis

• Incidence: 2.5-3 cases per 10,000 hospital admissions 2
• Rising incidence in recent years 3
• Pathogenesis occurs through:
  • Hematogenous spread (from skin, urinary tract, mouth, mastoid, or lung infections)
  • Direct extension (from vertebral osteomyelitis or discitis)
  • Trauma
  • Post-procedural complications (surgery, biopsy, lumbar puncture, anesthesia) 2

Microbiology

The most common causative organisms include:

• Staphylococcus aureus (approximately 63.6% of cases) 4
• Streptococcus species (6.8%) 4
• Aerobic gram-negative bacilli
• Anaerobes
• Less commonly: Nocardia species, mycobacteria, and fungi 2

Risk Factors

High-risk populations include patients with:

• Diabetes mellitus
• Intravenous drug use
• Cancer
• HIV infection
• Dialysis dependence
• Immunocompromised status
• Bacteremia
• Contiguous infections (psoas abscess, osteomyelitis, skin infections)
• Spinal instrumentation/procedures
• Alcohol abuse
• Hepatic or renal disease 1, 5

Clinical Presentation

The classic triad of symptoms includes:

• Back pain (most common, present in 70-90% of cases)
• Fever (absent in approximately 50% of cases)
• Neurological deficits (present in only about one-third of cases) 5

Important to note: The complete classic triad occurs in less than 8% of cases, making diagnosis challenging 1

Neurological manifestations may include:

• Motor weakness
• Sensory changes
• Urinary retention or incontinence
• Bowel dysfunction
• Hyperreflexia
• Radicular pain
• Spinal shock
• Cauda equina syndrome 5

Diagnostic Approach

Laboratory Studies

• Complete blood count (leukocytosis in approximately two-thirds of cases)
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) - elevated in most cases
  • ESR has 100% sensitivity and 67% specificity when combined with risk factors 5
• Blood cultures (positive in many cases)

Imaging

• MRI with gadolinium contrast is the gold standard diagnostic test with sensitivity of 96% and specificity of 94% 2, 6

  • Shows location and extent of abscess
  • Identifies spinal cord compression
  • Reveals associated osteomyelitis or discitis
  • Should include pre- and post-contrast images for comparison 2

• CT scan has limited utility:

  • Low sensitivity (6%) for epidural abscess detection
  • May show gross spinal canal compromise in advanced cases
  • Useful for surgical planning 2

• Plain radiographs:

  • Insensitive for epidural abscess detection
  • May show associated bony destruction in late stages
  • Not recommended as initial imaging 2

Management

Immediate Actions

1. Blood cultures before antibiotic administration
2. Prompt empiric antibiotic therapy:
   • Vancomycin (to cover MRSA)
   • Plus a third- or fourth-generation cephalosporin (for gram-negative coverage) 5

Definitive Management

Treatment approach depends on neurological status:

1. Surgical decompression plus antibiotics:

   • Indicated for patients with:
     • Neurological deficits
     • Spinal instability
     • Progressive symptoms despite antibiotics
     • Large abscesses causing significant compression

2. Medical management with antibiotics alone:

   • May be appropriate for:
     • Neurologically intact patients
     • Patients without significant cord compression
     • Patients with prohibitive surgical risks

Duration of Treatment

• Typically 4-6 weeks of antibiotics
• Guided by clinical response, inflammatory markers, and follow-up imaging

Prognosis and Complications

• Mortality rate: 5-16%
• Neurological recovery depends on:
  • Time to diagnosis
  • Severity of deficits before treatment
  • Prompt surgical decompression when indicated
• Up to 90% of patients are misdiagnosed on their first ED visit 1
• Delayed diagnosis significantly increases risk of permanent neurological damage

Key Pitfalls to Avoid

1. Relying on the classic triad - present in <8% of cases
2. Dismissing back pain without risk factor assessment
3. Delaying MRI in high-risk patients
4. Performing lumbar puncture - contraindicated due to risk of spreading infection
5. Waiting for fever - absent in half of cases
6. Delaying antibiotics while awaiting definitive diagnosis
7. Missing multifocal abscesses - consider imaging the entire spine

Early recognition, prompt imaging with MRI, and immediate treatment are essential to prevent devastating neurological outcomes in patients with spinal epidural abscess.