What is spondylodiscitis and how is it diagnosed and treated?

Spondylodiscitis: Definition, Diagnosis, and Treatment

Spondylodiscitis is a serious infection involving the vertebral body (spondylitis) and intervertebral disc (discitis) that requires urgent MRI imaging for diagnosis, tissue biopsy before antibiotics when feasible, and 6-12 weeks of antimicrobial therapy, with surgery reserved for neurological deficits, spinal instability, or treatment failure. 1

What is Spondylodiscitis?

Spondylodiscitis represents an infection of the vertebral endplate and adjacent disc space that typically occurs via hematogenous spread. 2 In adults, the disc is avascular and becomes infected following an initial septic embolus to the highly vascularized vertebral endplate, with subsequent spread across the disc to the opposing vertebral body. 2, 3

Key anatomical patterns:

• Single-level involvement occurs in 65% of patients 2, 4
• Contiguous multilevel infection occurs in approximately 20% of cases 2, 4, 3
• Non-contiguous multilevel disease occurs in about 10% of patients 2, 4, 3

Clinical presentation typically includes:

• Back pain (present in 85.3% of patients) combined with fever 1, 5
• Elevated inflammatory markers (ESR and CRP) 1
• Neurological deficits occur in up to 50% of patients when epidural extension or paravertebral abscesses compress nerve roots 3, 6

Most common causative organisms:

• Staphylococcus aureus accounts for up to 80% of pyogenic cases 5, 6
• Tuberculosis, brucellosis, and fungal pathogens are important non-pyogenic causes 1, 5

Diagnostic Approach

Initial Clinical Suspicion

Suspect spondylodiscitis in any adult presenting with new or worsening back/neck pain PLUS fever OR elevated ESR/CRP. 1 Do not rely on plain radiographs, as they lack sensitivity for early disease and changes may take months to appear. 1, 7

Imaging Strategy

MRI with contrast is the diagnostic modality of choice, demonstrating 96% sensitivity and 94% specificity. 1, 4 Obtain sagittal views of the entire spine to identify the full extent of involvement, epidural abscess formation, and paravertebral soft tissue extension. 1, 3

Classic MRI findings include:

• Focal or linear increased signal in adjacent vertebral endplates 2
• Involvement of the intervening disc space 1
• Endplate irregularities, erosions, or destruction on correlative CT 2
• Extension to epidural space or paravertebral soft tissues 2, 3

[18F]FDG PET/CT should be considered when:

• Symptoms are within 14 days of onset (before MRI changes develop) 1, 4
• MRI findings are inconclusive despite elevated inflammatory markers 1
• Evaluating for multilevel disease, given that 30% of cases involve multiple levels 1, 3

Microbiological Diagnosis

Obtain tissue diagnosis via image-guided or surgical biopsy BEFORE initiating antibiotics whenever possible, as biopsy has higher diagnostic yield than blood cultures. 1, 4 Blood culture positivity is only 53-54% in pyogenic and brucellar cases. 5 Tissue sampling with 16S rRNA PCR is superior to standard microbiological examination. 6

Exception to pre-treatment biopsy: If a patient had documented S. aureus bacteremia within the prior three months and MRI shows compatible spinal changes, treatment can be started directly without biopsy. 1

If the first biopsy is non-diagnostic, repeat sampling and specifically test for tuberculosis, brucellosis, and fungal pathogens. 1

Laboratory Evaluation

Measure ESR and CRP at baseline for monitoring treatment response. 1, 4 Pyogenic spondylodiscitis typically shows higher inflammatory markers compared to tuberculous or brucellar disease. 5

Treatment Algorithm

Antibiotic Therapy

Initiate empirical antibiotic therapy immediately after obtaining cultures (or immediately in septic/neurologically compromised patients), using vancomycin (15-20 mg/kg IV every 12 hours) combined with EITHER:

• Cefepime (2 g IV every 8-12 hours), OR 1, 4
• A carbapenem: meropenem (1 g IV every 8 hours), imipenem-cilastatin (500 mg IV every 6 hours), or ertapenem (1 g IV every 24 hours), OR 1, 4
• Ceftriaxone (2 g IV every 24 hours) plus metronidazole (500 mg IV every 8 hours) 1, 4

This regimen covers MRSA and gram-negative organisms. 1

Adjust antibiotics based on culture results and sensitivities once available. 1, 4

Duration and Route

Administer IV antibiotics for 2-4 weeks, then transition to oral antibiotics with excellent bioavailability. 1, 4, 6 Do NOT use oral β-lactams due to inadequate bioavailability. 1

Total treatment duration is 6-12 weeks. 1, 4 A randomized trial demonstrated that 6 weeks is non-inferior to 12 weeks, with clinical cure rates of 90.9% in both groups. 4

Switch to oral therapy when:

• CRP decreases 1
• Any significant epidural or paravertebral abscesses have been drained 1

Surgical Indications

Surgery is indicated for:

• Neurological deficits with spinal cord compression 1, 4, 6
• Progressive neurological deterioration 1
• Spinal instability or severe deformity 4, 6, 7
• Failure of conservative therapy with insufficient pain relief 4, 6, 7
• Need for tissue diagnosis when biopsy is non-diagnostic 4, 6, 7

Epidural abscess causing nerve root compression at multiple levels requires urgent surgical decompression. 1, 3 Paravertebral abscesses compressing exiting nerve roots in neural foramina necessitate drainage. 1, 3

Surgical approach options:

• Anterior approach allows for disc and bone debridement 7
• Posterior approach is indicated when posterior elements are involved or epidural abscess is present 7
• Instrumentation use in the presence of infection remains controversial 7

Monitoring Treatment Response

Monitor ESR and CRP as primary means to evaluate treatment response. 4, 6 A clear reduction in CRP and ESR in the first few weeks indicates good prognosis. 6 The treatment endpoint is normalization of inflammatory markers and osseous fusion of the mobile segment. 8

Critical Pitfalls to Avoid

Do not miss multilevel disease: Assess the entire spine with sagittal imaging, as 30% of cases involve multiple levels (20% contiguous, 10% non-contiguous). 1, 3 The valveless Batson plexus allows bidirectional blood flow, enabling bacterial seeding at multiple non-contiguous levels. 3

Do not delay imaging: Plain radiographs are inadequate for early diagnosis—proceed directly to MRI when clinical suspicion is high. 1, 7

Do not start antibiotics before obtaining tissue diagnosis unless the patient is septic, neurologically compromised, or has documented recent S. aureus bacteremia. 1 Premature antibiotics reduce diagnostic yield.

Do not use oral β-lactams for initial or early oral therapy due to inadequate bioavailability. 1

Monitor for treatment failure risk factors: Multidisc disease, concomitant epidural abscess, S. aureus infection, advanced age, diabetes, and significant comorbidities increase failure rates to 10-30%. 1, 5 Mortality is approximately 2-15% depending on severity. 6, 8

Watch for complications: Prolonged antibiotic treatment increases risk of drug intolerance and Clostridium difficile colitis. 1 Chronic back pain may persist even after successful infection clearance. 9