Tuberculous Osteomyelitis (Skeletal Tuberculosis)
High-Yield Revision Notes for NEET PG / NEXT
Skeletal tuberculosis accounts for approximately 10% to 15% of all extrapulmonary tuberculosis cases. It is caused by the hematogenous spread of Mycobacterium tuberculosis into bone tissue, characteristically targeting the vertebral bodies.
MRI Features: Demonstration of anterior vertebral involvement and a tracking paraspinal cold abscess causing structural narrowing.
Pathophysiology & Localization
- Primary Route: Arrives via hematogenous dissemination from a primary visceral focus (often subclinical pulmonary or lymphatic lesions). In spinal disease, spread occurs via the Batson’s paravertebral venous plexus.
- Anatomic Target: The spine is the most common site (50% of skeletal cases), termed Pott’s Disease. It classically begins in the anterior margin of the vertebral body near the subchondral bone plate.
- Paradiscal Spread: The infection routinely breaches the anterior or posterior longitudinal ligaments to track into adjacent vertebrae. Because the intervertebral disc is avascular, it resists early destruction and is squeezed or narrowed secondarily, contrasting with pyogenic infections where the disc is destroyed rapidly.
Key Subtypes & Named Lesions
| Condition / Sign | Anatomic / Diagnostic Features |
|---|---|
| Pott’s Spine | Most commonly affects the lower thoracic and upper lumbar vertebrae. Causes bone collapse leading to characteristically sharp, angular posterior spinal deformity (Gibbus deformity). |
| Cold Abscess | An accumulation of liquefactive caseous necrosis devoid of typical acute inflammatory signs (warmth, erythema). In the lumbar spine, it tracks along the psoas sheath to present as a groin mass (Psoas abscess). |
| Spina Ventosa | Tuberculous dactylitis involving the short tubular bones of the hands or feet in children. Manifests as a painless, expansile, “inflated” bone lesion with periosteal new bone formation. |
| Pott’s Paraplegia | Neurological deficit caused by mechanical spinal cord compression from an expanding cold abscess, caseous debris, granulation tissue, or bony subluxation. |
Diagnostic Workup
- Magnetic Resonance Imaging (MRI): The initial imaging modality of choice for spinal involvement. It excels at demonstrating early marrow edema, subligamentous tracking of collections, and detailing spinal cord compromise.
- Histopathology (Definitive Standard): CT-guided fine-needle aspiration or core bone biopsy reveals pathognomonic caseating granulomas with Langhans giant cells and epithelioid histiocytes.
- Microbiology & Molecular Diagnostics: Ziehl-Neelsen staining captures Acid-Fast Bacilli (AFB). Cartridge Based Nucleic Acid Amplification Test (CBNAAT / GeneXPT) is used preferentially due to rapid turnaround and concurrent detection of rifampicin resistance mutations.
Management Protocol
- Medical Therapy (Primary Axis): Standard multi-drug Anti-Tubercular Therapy (ATT). Skeletal tuberculosis routinely demands extended course treatment durations ranging from 9 to 12 months, contrasting with standard pulmonary regimens.
- Surgical Indications: Reserved for cases with progressive neurological deficits (Pott’s paraplegia), severe spinal instability, significant kyphotic deformity development, or failure to respond to medical therapy.