Discitis-Osteomyelitis

Figure 1: Lateral chest radiograph of a 76-year-old man with back pain shows destruction of mid-thoracic disc space (star).
Figure 2: Sagittal reformatted CT image (myelogram) shows destruction (star) of the disk space, opposing endplates and epidural extension of soft tissue (arrowheads) seen as filling defect on this myelographic study.

Facts: Spinal Infections

• A spectrum of diseases - osteomyelitis (spondylitis), discitis, discitis-osteomyelitis, epidural abscess
• Of all osteomyelitis, spine accounts for 2% - 4% of anatomic sites
• When spinal infection involves thoracic spine, neurologic compromise is a concern
• Patients at risk include diabetes, IV drug user, chronic delibitating disease, immunosuppression, recent vertebral surgery
• Most common clinical presentation = axial back pain, constant, not relieved by rest (night pain is a red flag for infection or neoplasm)
• Most spinal infections are due to bacterial infection (>50%, S. aureus); definitive diagnosis made by culture from blood or biopsy

Imaging

• Plain radiography: disc space narrowing (2-3 weeks of infection) --> endplate sclerosis (8-12 weeks) --> bony lysis --> vertebral body collapse resulting in localized kyphosis
• CT: more bony details, with myelography it can delineate the degree of spinal canal encroachment
• MRI: best imaging method to assess spinal infection; high sensitivity/specificity/accuracy (more than 90%)
• Features: disc destruction (narrowing, signal change), endplate destruction, abscess, epidural extension, posterior element involvement
• Think of TB if: late clinical presentation, extensive paravertebral abscess, relative preservation of disc, subligamentous spread

Our case: Discitis-osteomyelitis from Staphylococcus aureus.

References:

1. An HS, Seldomridge JA. Spinal infections diagnostic tests and imaging studies. Clin Orthop Rel Res 2006;444:27-33