In an adult with persistent back pain, possible fever and elevated inflammatory markers, what is the appropriate diagnostic work‑up for suspected spondylodiscitis?

Diagnostic Work-Up for Suspected Spondylodiscitis

In an adult with persistent back pain, fever, and elevated inflammatory markers, obtain MRI with contrast of the entire spine immediately—this is the diagnostic modality of choice with 96% sensitivity and 94% specificity—and secure a microbiological diagnosis via image-guided biopsy before starting antibiotics whenever clinically feasible. 1

Clinical Suspicion Triggers

Suspect spondylodiscitis when you encounter:

• New or worsening back/neck pain combined with fever 2
• New or worsening back/neck pain with elevated ESR or CRP 2
• Back pain lasting 14-90 days with systemic inflammatory signs 3, 4
• Diabetes mellitus (present in 75% of cases), recent bacteremia, endocarditis, or immunocompromised state 3, 4

Imaging Algorithm

First-Line: MRI with Contrast

• Order sagittal MRI views of the entire spine, not just the symptomatic region 1
• MRI demonstrates 96% sensitivity and 94% specificity and is essential to assess epidural extension, nerve root compression, and paravertebral soft tissue involvement 1
• Critical pitfall: 30% of cases involve multiple levels (20% contiguous, 10% non-contiguous), so imaging only the painful segment will miss disease 1, 5, 3

When to Add [18F]FDG PET/CT

Consider PET/CT in three specific scenarios:

• Symptoms present ≤14 days (MRI changes may not yet be evident) 1
• MRI findings inconclusive despite elevated inflammatory markers 1
• To evaluate for multilevel disease, particularly in IV drug users, post-surgical patients, or those with recent bacteremia 1, 5

CT Imaging Role

• Use CT when MRI is contraindicated (pacemakers, severe claustrophobia) 1
• CT evaluates bony destruction, neuroforaminal stenosis, and guides biopsy 1
• Non-sclerotic endplate erosions on CT predict positive microbiology in 54.5% of cases 6

Plain Radiographs

• Do not rely on plain films—they lack sensitivity for early diagnosis 2
• Radiographs may show irregularities, erosions on opposing vertebral bodies, reactive sclerosis, and reduced disc space only in established disease 7

Laboratory Evaluation

Obtain baseline inflammatory markers:

• ESR and CRP for monitoring treatment response 1
• CRP >50 mg/L increases likelihood of positive biopsy microbiology to 63.6% 6
• Blood cultures (positive in approximately 50% of cases) 4

Microbiological Diagnosis—The Critical Step

Obtain tissue diagnosis via image-guided or surgical biopsy before initiating antibiotics whenever the patient is not septic or neurologically compromised 2, 1:

• Biopsy has higher diagnostic yield than blood cultures alone 1
• CT-guided biopsy is the standard approach 6
• Submit specimens for aerobic, anaerobic, mycobacterial (tuberculosis), brucellosis, and fungal cultures 1
• If the first biopsy is non-diagnostic, repeat sampling with specific testing for TB, brucellosis, and fungal pathogens 1

Predictors of Positive Biopsy

The combination of paravertebral abscess + non-sclerotic endplate erosions has 100% specificity for positive microbiology 6. Other high-yield combinations include:

• Paravertebral abscess + CRP >50 mg/L (96.6% specificity) 6
• Non-sclerotic endplate erosions + CRP >50 mg/L (96.6% specificity) 6

Exception to Pre-Treatment Biopsy

Skip biopsy and proceed directly to treatment only when: S. aureus bloodstream infection occurred within the preceding 3 months AND MRI shows compatible spine changes 2. This scenario alone provides sufficient microbiologic diagnosis.

Key Imaging Findings to Document

On MRI, identify and report:

• Vertebral endplate involvement (initial infection site in adults) 3
• Adjacent disc space involvement (infection spreads from endplate across avascular disc) 2, 3
• Epidural abscess formation (present in 75% with neurological deficits) 3
• Paravertebral soft tissue extension and abscesses (compress nerve roots in neural foramina) 1, 5
• Number and location of all involved levels (single-level in 65%, contiguous multilevel in 20%, non-contiguous in 10%) 3

Critical Diagnostic Pitfalls to Avoid

1. Missing multilevel disease: Always image the entire spine—20% have contiguous multilevel involvement and 10% have non-contiguous disease at distant levels 1, 5, 3

2. Starting antibiotics before biopsy: Except in septic or neurologically compromised patients, withhold empiric therapy until microbiologic diagnosis is secured 2, 1

3. Relying on plain radiographs: They are insensitive early in disease when intervention is most effective 2

4. Imaging only the symptomatic region: Symptoms may not correlate with all sites of infection, particularly in non-contiguous multilevel disease 5

5. Misdiagnosing as degenerative disease: Spondylodiscitis is frequently mismanaged initially as degenerative pathology, delaying diagnosis by months 2

Diagnostic Timeline Expectations

• Symptom duration before diagnosis typically ranges 14-90 days 3, 4
• Early in the disease course, radiographic changes may be absent despite active infection 3
• This insidious presentation explains why diagnosis is often delayed and why clinical suspicion based on the combination of back pain + fever or back pain + elevated inflammatory markers must trigger immediate MRI 2, 3