What is the differential diagnosis for a patient presenting with spondylodiscitis and multilevel radiculopathy?

Differential Diagnosis of Spondylodiscitis with Multilevel Radiculopathy

The differential diagnosis must distinguish between infectious spondylodiscitis and several non-infectious mimics, while simultaneously recognizing that multilevel involvement in spondylodiscitis itself can present as either contiguous spread (20% of cases) or non-contiguous disease from multiple septic emboli (10% of cases). 1

Primary Infectious Considerations

Spondylodiscitis Patterns Themselves

• Contiguous multilevel spondylodiscitis occurs when infection spreads sequentially from one disc-vertebral unit to adjacent levels, creating a continuous column of inflammation affecting multiple nerve root levels (approximately 20% of cases). 1, 2
• Non-contiguous multilevel spondylodiscitis presents with separate infection foci at distant spinal levels from multiple septic emboli during bacteremia, creating independent sites of nerve root compression (approximately 10% of cases). 1, 2, 3
• Tuberculous spondylodiscitis has an insidious clinical presentation resulting in delayed diagnosis and should be considered when initial biopsies are non-diagnostic. 3, 4

Mechanisms of Radiculopathy in Confirmed Spondylodiscitis

• Epidural abscess formation from posterior extension directly compresses nerve roots and spinal cord, spanning multiple vertebral levels and causing compression at each affected level. 1
• Paravertebral abscess spreads laterally into soft tissues, compressing exiting nerve roots in neural foramina at multiple levels. 1

Non-Infectious Differential Diagnoses

Degenerative and Mechanical Conditions

• Intervertebral erosive osteochondrosis can mimic the disc space narrowing and endplate irregularities seen in spondylodiscitis but lacks the inflammatory markers and contrast enhancement pattern. 4, 5
• Modic type 1 endplate changes demonstrate increased signal intensity on MRI similar to early spondylodiscitis but typically lack the severe disc space involvement and paravertebral soft tissue changes. 4
• Severe degenerative arthritis may show disc space narrowing and endplate sclerosis but differs in the pattern of bone changes and absence of soft tissue inflammation. 5

Inflammatory Arthropathies

• Axial spondyloarthropathy can present with inflammatory back pain and vertebral body changes but typically shows different distribution patterns and lacks the disc-centered pathology. 4
• Hemodialysis spondyloarthropathy occurs in patients on chronic dialysis and can mimic infectious spondylodiscitis with destructive vertebral changes. 4

Neurological Conditions

• Charcot's axial neuroarthropathy presents with progressive vertebral destruction in patients with sensory neuropathy but has a distinct clinical context and imaging pattern. 4

Neoplastic Conditions

• Metastatic disease or primary spinal tumors must be excluded, particularly when single vertebral body involvement is present initially, as early spondylodiscitis can present atypically with only single vertebral involvement before classic two-adjacent-vertebrae pattern develops. 4, 6

Critical Diagnostic Imaging Features

MRI Characteristics Favoring Spondylodiscitis

• Classic pattern: Increased signal intensity in two adjacent vertebral bodies with intervening disc space involvement and contrast enhancement. 1, 7
• Epidural extension: Ringlike enhancement on gadolinium-enhanced MRI in epidural abscess lesions is a specific indicator requiring surgical consideration. 8
• Paravertebral soft tissue involvement: Increased signal in paravertebral musculature with contrast enhancement supports infectious etiology. 7

Atypical Presentations Requiring High Suspicion

• Single vertebral body involvement can represent early spondylodiscitis before classic imaging findings develop, leading to diagnostic delay if not recognized. 6
• Irregular cavitations (bone caries) surrounded by reactive sclerosis in the vertebral body near the frontal plate occur in 50% of chronic cases. 5
• Bone erosions on anterior cortical surface of vertebral body may represent a specific sign of chronic spondylodiscitis. 5

Diagnostic Algorithm for Multilevel Cases

Initial Imaging Assessment

• MRI with contrast is essential (sensitivity 96%, specificity 94%) to assess full extent of epidural and soft tissue involvement, with sagittal views critical for identifying all levels. 1, 2
• [18F]FDG PET/CT is particularly valuable for detecting multilevel disease and is the preferred modality within the first 14 days of symptom onset. 1, 2

Laboratory Markers

• Elevated ESR and CRP with or without leukocytosis support infectious etiology but are non-specific. 7, 5
• Negative blood cultures occur frequently and should not exclude diagnosis; biopsy-guided or surgical biopsy has higher diagnostic yield. 2, 7

Microbiological Confirmation

• CT-guided needle biopsy should be performed when possible before initiating antibiotics, though negative cultures do not exclude diagnosis. 2, 3, 7
• If first biopsy is non-diagnostic, consider additional testing for tuberculosis, brucellosis, or fungal pathogens. 3

Common Pitfalls to Avoid

• Misdiagnosing as myofascial pain when patients present with back pain without fever, particularly in previously healthy middle-aged individuals. 7
• Dismissing multilevel involvement as too atypical for spondylodiscitis when in fact 30% of cases involve multiple levels (20% contiguous, 10% non-contiguous). 1, 2
• Waiting for classic two-vertebrae pattern when early disease may show only single vertebral body involvement initially. 6
• Relying solely on blood cultures for pathogen identification when biopsy has superior diagnostic yield. 2