Could the lumbar MRI findings of discogenic disease, spondylosis, foraminal stenosis, fluid in the left L5‑S1 disc space with adjacent end‑plate irregularity and edema represent discitis or osteomyelitis, and what diagnostic work‑up and management steps are recommended?

Diagnostic Work-Up and Management of Suspected Discitis/Osteomyelitis at L5-S1

You must obtain an MRI of the lumbar spine with and without intravenous contrast immediately to definitively distinguish between degenerative disc disease and infectious discitis/osteomyelitis. 1

Why Contrast-Enhanced MRI is Essential

The findings described—fluid in the L5-S1 disc space with adjacent end-plate irregularity and edema—create diagnostic ambiguity that cannot be resolved without contrast enhancement. 1

• MRI without and with IV contrast achieves 96% sensitivity, 94% specificity, and 92% accuracy for diagnosing spinal infection, making it the gold standard imaging modality. 1, 2
• Contrast enhancement is critical because it reveals the presence and extent of enhancement in the disc space, end-plates, and surrounding soft tissues—key features that differentiate infection from degenerative changes. 1
• Pre-contrast sequences must be obtained for comparison to confirm areas of abnormal enhancement; performing MRI with contrast only is inadequate and may lead to false negatives. 1, 2
• Epidural enhancement combined with abnormal laboratory values (elevated ESR, CRP, or white blood cell count) significantly increases the predictive value of a positive biopsy for spondylodiscitis. 1, 3

Critical Imaging Features to Assess

When reviewing the contrast-enhanced MRI, look for these specific findings:

Features Favoring Infection (Discitis/Osteomyelitis):

• Contrast enhancement of the disc space and adjacent vertebral end-plates is the hallmark of active infection. 1
• Paraspinal or epidural soft tissue enhancement or abscess formation strongly suggests infection. 1, 3
• Diffusion restriction on diffusion-weighted imaging (DWI) helps differentiate acute infectious spondylitis from reactive (Modic type 1) degenerative end-plate changes. 1, 3
• Destruction of two or more contiguous vertebrae with opposing end-plate involvement and spread along the anterior longitudinal ligament suggests tuberculous spondylitis. 3

Features Favoring Degenerative Disease:

• Absence of contrast enhancement in the disc space and end-plates argues against active infection. 1
• Modic type 1 changes (end-plate edema on T2-weighted images with hypointensity on T1) can mimic infection but typically lack the robust enhancement seen in discitis. 1, 4
• Vacuum disc phenomenon (gas in the disc space) is pathognomonic for degenerative disease and excludes infection. 5, 6

Laboratory and Microbiological Work-Up

While awaiting or immediately after obtaining the MRI, perform the following:

• Obtain inflammatory markers: Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) have high sensitivity for bacterial discitis/osteomyelitis, though specificity is low. 4, 7
• Blood cultures: Draw at least two sets before initiating antibiotics, as hematogenous spread is the most common route of spontaneous discitis. 7
• Consider tuberculin skin test (PPD) or interferon-γ release assay if the patient has epidemiologic risk factors for tuberculosis (endemic region, immunosuppression, prior TB exposure). 3
• CT-guided percutaneous biopsy of the disc space should be performed if MRI findings are equivocal or if microbiological confirmation is needed before starting prolonged antimicrobial therapy. 1 Biopsy is particularly useful when blood cultures are negative, which occurs in up to 50% of cases. 7

Alternative Imaging if MRI is Contraindicated

If the patient cannot undergo MRI (e.g., pacemaker, severe claustrophobia, metallic implants causing artifact):

• FDG-PET/CT is the second-line modality, with 94.8% sensitivity and 91.4% specificity for spinal infection. 2
• CT with contrast can evaluate for end-plate erosion, paraspinal soft tissue changes, and guide biopsy, but has lower sensitivity (79%) than MRI for detecting early infection. 1
• Combined gallium-67/Tc-99m bone scan provides approximately 78% sensitivity and 81% specificity for spinal infection when MRI is unavailable. 2, 3

Management Algorithm

If MRI Confirms Infection:

1. Initiate empiric intravenous antibiotics targeting Staphylococcus aureus (most common pathogen) after obtaining blood cultures and/or biopsy. 7
2. Spinal immobilization with a brace to reduce pain and prevent instability. 7
3. Surgical intervention is reserved for patients with spinal instability, cord compression, epidural abscess, or failure of medical therapy after 4-6 weeks. 1, 7
4. Monitor clinical response with serial ESR/CRP and follow-up MRI at 4-6 weeks; imaging findings lag behind clinical improvement. 1, 3

If MRI Confirms Degenerative Disease:

1. Conservative management with physical therapy, NSAIDs, and activity modification. 8, 5
2. Consider epidural steroid injections for radicular symptoms if foraminal stenosis is contributing. 8
3. Surgical fusion may be considered for refractory discogenic pain, but only after exhausting conservative measures and ideally with confirmatory discography (though discography alone is not recommended for treatment decisions). 1

Common Pitfalls to Avoid

• Do not rely on non-contrast MRI alone; the absence of contrast limits your ability to detect active infection. 1, 2
• Do not assume degenerative changes exclude infection; both can coexist, and infection can occur in a previously degenerated disc. 4, 7
• Do not delay biopsy if clinical suspicion is high despite equivocal imaging; microbiological confirmation guides targeted antibiotic therapy. 1, 7
• Do not interpret elevated inflammatory markers as diagnostic; they are sensitive but not specific, and non-infectious inflammatory conditions (e.g., CPPD spondyloarthropathy, gout) can mimic infection. 4