How does spondylodiscitis lead to multilevel radiculopathy?

How Spondylodiscitis Causes Multilevel Radiculopathy

Spondylodiscitis causes multilevel radiculopathy through direct extension of infection to the epidural space, paravertebral soft tissues, and posterior spinal elements, resulting in nerve root compression at multiple levels—a pattern that occurs in approximately 20% of cases with contiguous multilevel involvement and 10% with non-contiguous multilevel disease. 1, 2

Pathophysiological Mechanisms

Primary Infection Pathway

• The infection typically begins with hematogenous seeding of bacteria (most commonly Staphylococcus aureus) to the highly vascular vertebral endplate 3, 4
• Since the intervertebral disc is avascular in adults, infection spreads from the initial vertebral endplate focus into the adjacent disc space and then to the opposing vertebral body 1
• This creates the classic pattern of two adjacent vertebral bodies with intervening disc involvement 4, 5

Extension Patterns Leading to Radiculopathy

Epidural Space Involvement:

• Infection extends posteriorly into the epidural space, creating epidural abscesses that directly compress nerve roots and the spinal cord 1, 3
• Neurological deficits occur in up to 50% of patients with spondylodiscitis, primarily due to this epidural extension 3
• The epidural abscess can span multiple vertebral levels, causing compression of nerve roots at each affected level 1

Paravertebral and Soft Tissue Extension:

• Infection spreads laterally into paravertebral soft tissues and can form paravertebral abscesses 1, 6
• These collections compress exiting nerve roots in the neural foramina at multiple levels 4
• Tuberculous spondylodiscitis is particularly associated with psoas and paravertebral abscesses that can track along fascial planes 3

Posterior Element Involvement:

• The infection can extend to involve the posterior elements of the vertebrae (pedicles, laminae, facet joints) 1, 6
• This posterior extension creates additional sites of nerve root compression and can contribute to spinal instability 3

Multilevel Disease Patterns

Contiguous Multilevel Infection

• Approximately 20% of spondylodiscitis cases involve contiguous multilevel infection, where the infectious process spreads sequentially from one disc-vertebral unit to adjacent levels 1, 2
• This creates a continuous column of inflammation and abscess formation affecting multiple nerve root levels 1

Non-Contiguous Multilevel Infection

• About 10% of cases present with non-contiguous multilevel infections, where separate foci of infection occur at distant spinal levels 2, 7, 8
• This pattern results from multiple septic emboli during bacteremia, creating independent sites of nerve root compression 1

Clinical Implications

Common Pitfalls:

• Single-level vertebral body involvement can occur early in the disease course before classic imaging findings develop, potentially delaying diagnosis 5
• The insidious clinical presentation with nonspecific back pain often results in diagnostic delay, allowing time for multilevel extension to develop 4, 9
• Neurological deficits represent the most severe complication and indicate epidural extension requiring urgent evaluation 3, 9

Diagnostic Considerations:

• MRI with contrast is essential to assess the full extent of epidural and soft tissue involvement causing nerve root compression 8, 6
• Sagittal imaging views are critical to identify all levels of involvement and epidural extension 1
• [18F]FDG PET/CT is particularly valuable for detecting multilevel disease and is recommended for evaluation of multilevel spondylodiscitis 1

Treatment Urgency:

• Surgical intervention is indicated when neurological deficits with spinal cord compression are present, as this represents direct mechanical compression from epidural abscess or soft tissue extension 2, 3
• The presence of multilevel radiculopathy suggests extensive disease requiring aggressive treatment to prevent permanent neurological damage 3, 9