A 28-year-old man from a TB-endemic region presents with progressive thoracic kyphosis, paraparesis, and an extradural soft tissue mass at T8–T9 level on MRI. The 'paradoxical disc sparing' seen early in TB spondylitis occurs because:

• A Mycobacteria preferentially secrete collagenase targeting bone not proteoglycans
• B Disc space infection is masked by epidural abscess
• C The disc is primarily avascular in adults, so hematogenous spread bypasses the disc initially ✓
• D Anti-tubercular drugs penetrate disc better than bone

Explanation

In pyogenic vertebral osteomyelitis, bacteria home to the disc via arterial supply (the disc has dual blood supply from adjacent vertebral body end-arteries in children), so disc destruction is early. In TB spondylitis (Pott's disease), the disc is initially spared because in adults the intervertebral disc is avascular; Mycobacterium tuberculosis spreads hematogenously to the highly vascular vertebral body metaphysis (just beneath the endplate) and erodes into the disc from adjacent bone. Early disc preservation with anterior vertebral body destruction ('anterior corner sign') is a classical radiological distinction of TB from pyogenic spondylitis.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.