Two patients present with back pain. Patient X has 10 days of high fever with complete destruction of the intervertebral disc on MRI. Patient Y has 4 months of low-grade fever with vertebral body destruction but a comparatively well-preserved disc space. The reason the disc survives longer in Patient Y's condition is:

• A Granulation tissue in tuberculosis grows away from the end plates
• B The disc is avascular and therefore protected from haematogenous infection
• C Tuberculous bacilli preferentially colonise the anterior longitudinal ligament
• D Mycobacterium tuberculosis lacks the proteolytic enzymes that rapidly destroy cartilage and disc tissue ✓

Explanation

Pyogenic organisms release potent proteolytic enzymes that destroy the disc within days, whereas Mycobacterium tuberculosis produces no such enzymes, so the disc is destroyed late and mainly by direct extension of disease from the adjacent vertebral bodies. This relative preservation of disc space is a key discriminator favouring tuberculosis over pyogenic spondylodiscitis. The disc being avascular explains its vulnerability to infection generally, not its survival in tuberculosis.

Reference: Tuli's Textbook of Tuberculosis of the Skeletal System, 5th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.