POTT'S SPINE (Tuberculosis of the Spine)

Complete 15-Mark MD Examination Answer

1. DEFINITION & HISTORICAL NOTE

2. EPIDEMIOLOGY & INCIDENCE

• Skeletal TB constitutes 10% of all extra-pulmonary TB (EPTB) in immunocompetent individuals.
• The spine is the most frequently affected skeletal site (~50% of skeletal TB cases).
• Most common in children and young adults in developing countries.
• Haematogenous spread from a primary focus (lung, lymph node, genitourinary tract) is the usual route.

3. PATHOGENESIS

1. Batson's paravertebral venous plexus (haematogenous route — commonest)
2. Direct spread from adjacent paravertebral lymph nodes
3. Direct contiguous spread from adjacent vertebral bodies

Types of Lesion (by site within vertebra):

Pathological Sequence:

• Infection begins in cancellous area of vertebral body (usually epiphyseal location).
• TB produces exudative reaction with hyperaemia → destroys epiphyseal cortex → spreads to intervertebral disc and adjacent vertebra.
• Spreads beneath the anterior longitudinal ligament to reach neighbouring vertebrae.
• Vertebral body becomes soft → anterior wedging (thoracic > others due to kyphotic curve) or total collapse.
• Sequestrum: single large caseating lesion → calcifies centrally; mechanical strength reduced less.
• With healing: exudate reabsorbed, osteoporosis decreases, adjacent bodies fuse.

4. SITES OF INVOLVEMENT

• Thoracic spine (dorsal): most common (especially D6–D12), kyphosis more severe, highest risk of paraplegia.
• Thoracolumbar junction (D12–L1): second most common.
• Lumbar spine: relatively less severe deformity (lordotic curve shifts gravity posteriorly → minimal wedging).
• Cervical spine: least common; retropharyngeal abscess typical.
• Multifocal involvement (skip lesions) in ~4–5% of cases.

5. CLINICAL FEATURES

Symptoms:

• Pain (most common presenting complaint) — insidious onset, localised to the spine, worse on exertion.
• Stiffness of the spine — early protective sign.
• Constitutional symptoms: fever (low-grade), evening rise of temperature, night sweats, anorexia, weight loss.
• Deformity: Gibbus (angular kyphosis) — pathognomonic of Pott's spine; most prominent in thoracic disease.
• Neurological symptoms: weakness/paralysis of lower limbs (Pott's paraplegia), bladder/bowel dysfunction.

Signs:

• Muscle spasm obliterates normal spinal curves; all spinal movements restricted and painful.
• Careful palpation, percussion, or pressure reveals tenderness over affected vertebrae.
• "Boggy, dusky thickening" of skin over affected area (in some patients).
• Knuckle kyphosis (localised angular gibbus) — obvious when vertebral wedging and collapse have occurred.
• Stiff back test (child with spinal TB picks objects off the floor by squatting with spine straight, holding the head with hands).

Abscess Signs:

• Cervical: retropharyngeal swelling (dysphagia, stridor), collar-stud abscess in neck.
• Thoracic: paravertebral fusiform soft-tissue shadow on CXR; may track to mediastinum.
• Thoracolumbar: psoas abscess → track down iliacus sheath → point in iliac fossa, Scarpa's triangle, gluteal region, or behind the inguinal ligament.
• Lumbar: psoas abscess common; may point at anterior superior iliac spine.

6. COLD ABSCESS (Psoas Abscess)

• Formed by liquefied caseation and accumulation of TB pus without classic signs of inflammation (no redness, heat, or local throbbing).
• Routes of tracking:
  • Behind inguinal ligament → femoral triangle (Scarpa's triangle)
  • Along femoral/gluteal vessels → gluteal region
  • Upward into the mediastinum (thoracic lesions)
  • Down the thigh to the medial side of the knee (rarely)
• In cervical TB: retropharyngeal abscess may compress the airway.
• A long-standing, tense paravertebral abscess can cause aneurysmal excavation of the vertebral body.

7. POTT'S PARAPLEGIA

1. Diameter and space of spinal canal are smallest in the dorsal region.
2. Abscess remains under tension and is forced into the spinal canal.
3. TB infection is most common in this area.
4. Spinal cord terminates below L1, so cord (not cauda equina) is at risk.

Mechanisms — Table 19.1 from Sharma & Mohan:

• Cold abscess (fluid or caseous material)
• Granulation tissue
• Sequestrated bone and disc fragments
• Pathological subluxation or dislocation of vertebra

• Fibrous or bony ridges
• Healed retropulsed bony fragments

• Thrombosis/endarteritis of spinal vessels (arteritis)
• Myelitis due to direct TB invasion
• Syrinx formation
• Epidural abscess with cord compression

Types of Pott's Paraplegia:

8. DEFORMITY: THE GIBBUS

• Kyphosis (gibbus) develops due to anterior collapse of vertebral bodies.
• Most marked in thoracic spine (gravity + natural kyphotic curve).
• In cervical and lumbar spine, wedging is minimal (centre of gravity posteriorly located).
• Scoliosis: lateral deviation from asymmetric vertebral destruction.
• In very rare cases, vertebral body may dislocate anteriorly due to destruction of pedicles.

Predicting Final Gibbus Angle (Formula — Sharma & Mohan):

y = a + bx

• y = final angle of gibbus
• a = 5.5 (constant)
• b = 30.5 (constant)
• x = amount of initial loss of vertebral body height (vertebral body height divided into 10 equal parts; loss of each contiguous affected vertebra summed)

9. RADIOLOGICAL FEATURES

Plain X-Ray (Earliest and Most Important):

• Reduction in disc space — earliest sign (due to disc destruction).
• Rarefaction (osteoporosis) of adjacent vertebral bodies.
• Anterior wedging of vertebral body → angular kyphosis (gibbus).
• Paravertebral shadow: fusiform opacity (psoas abscess) — best seen in dorsal and lumbar regions.
• Calcification within abscess (in chronic/healing disease).
• Loss of psoas shadow on one/both sides.

CT Scan:

• Better delineation of bony destruction, sequestra, and extent of abscess.
• CECT abdomen: hypodense paravertebral/psoas collection with ring enhancement.
• Helps plan surgical approach.

MRI (Gold Standard for Spinal TB):

• Earliest and most sensitive investigation.
• Sagittal T1: hypointense vertebral bodies and disc (L1 and L2 example — Fig 19.6B).
• Sagittal T2: hyperintense vertebral bodies and epidural soft tissue (Fig 19.6C).
• Shows extent of cord compression, epidural abscess, cord signal changes.
• Defines subligamentous spread and skip lesions.
• T1 with gadolinium: bright enhancement of affected vertebrae and epidural soft tissues.

10. DIFFERENTIAL DIAGNOSIS

• Developmental defects: hemivertebra, Calvé's disease, Schmorl's nodes, Scheuermann's disease.
• Pyogenic spondylitis (staphylococcal, Brucella) — more acute, rapid destruction, fever.
• Metastatic carcinoma — usually in older patients; disc preserved until late.
• Multiple myeloma.
• Lymphoma.
• Eosinophilic granuloma (Langerhans cell histiocytosis).
• Sarcoidosis.
• Ankylosing spondylitis.

• Disc involved early (TB); disc spared till late (malignancy).
• Cold abscess typical of TB.
• Gibbus (angular kyphosis) characteristic of TB.
• MRI showing subligamentous spread and large abscess favours TB.

11. DIAGNOSIS

1. Clinical + Radiological (plain X-ray, CT, MRI) — usually sufficient.
2. ESR, CRP — elevated; non-specific.
3. Mantoux test — supportive; negative in immunocompromised.
4. CT-guided biopsy — for histopathology (caseating granuloma with Langhans' giant cells) and culture.
5. CBNAAT (Xpert MTB/RIF) — increasingly used for bone and joint TB:
   • Bone and joint fluid: pooled sensitivity 97.2%, specificity 90.2%.
   • Bone and joint tissue: sensitivity 94.6%, specificity 85.3%.
6. Culture on Lowenstein-Jensen medium — gold standard for confirmation and DST; slow (6–8 weeks).

12. MANAGEMENT

A. Anti-Tuberculosis Treatment (ATT)

• Standard regimen: 2HRZE + 4–7HR (total 9–12 months, extended up to 18 months in complicated cases).
• Drugs: H (Isoniazid), R (Rifampicin), Z (Pyrazinamide), E (Ethambutol).
• Response monitored by clinical improvement (pain relief, muscle spasm reduction) and radiological improvement (bone density restoration, fusion).
• Most patients respond well to conservative ATT alone.

B. Immobilisation

• Bed rest (absolute in early/active disease).
• Spinal orthoses/braces (thoracic/lumbar corsets, cervical collar) — maintain alignment, prevent deformity progression, relieve pain.
• Not required after bony fusion is achieved.

C. Surgical Treatment

1. Doubtful diagnosis where open biopsy is required.
2. Large abscess not responding to aspiration.
3. Significant spinal instability.
4. Progressive deformity despite adequate ATT.

• Paraplegia not recovering with conservative ATT (mechanical compression).
• Rapid onset or progressive paraplegia.
• Late-onset paraplegia (healed disease with fibrous/bony cord compression).

Surgical Options:

1. Anterior decompression (Hong Kong operation / anterior debridement and fusion): standard approach for dorsal spine TB with cord compression; decompression of cord by extensive anterior debridement + bone grafting.
2. Posterior laminectomy: less favoured (cord still compressed anteriorly; risk of spinal instability).
3. Combined anterior–posterior stabilisation: for severe deformity and instability.
4. Drainage of abscess: CT-guided aspiration or open drainage.
5. CT-guided transpedicular biopsy: for diagnosis.

Treatment of Pott's Paraplegia:

• Early onset (active disease): ATT + decompression + bone grafting.
• Late onset (healed disease): Anterior radical decompression essential (no response to ATT expected).
• Medical paraplegia (non-mechanical / vascular): ATT alone; steroids may be added.

13. PROGNOSIS

• With timely ATT, majority of patients recover completely.
• Neurological recovery is good for early-onset paraplegia (mechanical, active disease) — up to 80–90% with decompression.
• Late-onset paraplegia has a poorer prognosis without surgery.
• Residual deformity (gibbus) persists; can cause cosmetic and cardiopulmonary problems in severe cases (restrictive lung disease from thoracic kyphosis).

SUMMARY TABLE — HIGH-YIELD POINTS FOR MD EXAM

• Sharma SK, Mohan A (Eds). Textbook of Tuberculosis and Nontuberculous Mycobacterial Diseases, 3rd Ed. Chapter 19: Skeletal Tuberculosis (S Bhan, HL Nag), pp 267–293. Jaypee Brothers Medical Publishers, New Delhi.
• Sharma SK, Mohan A (Eds). Chapter 20: Musculoskeletal Manifestations of Tuberculosis (Aman Sharma, Kusum Sharma), pp 294–301.