Pott's Disease (Spinal Tuberculosis) - 10 Marks Answer

Definition

Sites of Involvement

• Lower thoracic and lumbar vertebrae are the most common sites, followed by the middle thoracic and cervical vertebrae.
• Usually two contiguous vertebrae are involved, but several vertebrae can be affected.
• Skip lesions (non-contiguous vertebrae) may occur in ~7% of cases.
• Paradiscal involvement is the most common radiological type, followed by central, anterior, and appendicial types.

Pathology

Infection of Bone

• Begins in the cancellous area of the vertebral body, most commonly in the epiphyseal location.
• TB produces an exudative reaction with hyperaemia.
• Infection spreads and destroys the epiphyseal cortex, intervertebral disc, and adjacent vertebrae.
• May spread beneath the anterior longitudinal ligament to reach neighbouring vertebrae.
• The vertebral body becomes soft and collapses, producing anterior wedging (common in thoracic spine) or total collapse.
• With healing, the adjacent vertebral bodies may fuse.

Formation of Cold Abscess

• The exudate (serum, leucocytes, caseous material, bone fragments, and TB bacilli) penetrates ligaments and follows fascial planes to form a "cold abscess".
• Cervical region: Retropharyngeal abscess; may track to the mediastinum or neck (sternomastoid abscess).
• Thoracic spine: Fusiform/bulbous paravertebral abscess ("bird-nest appearance"); may compress the spinal cord.
• Lumbar region: Enters the psoas sheath → psoas abscess, palpable in the iliac fossa. Can gravitate to the thigh, Scarpa's triangle, or gluteal region.

Clinical Features

• Constitutional symptoms (weakness, weight loss, evening fever, night sweats) usually precede spinal symptoms.
• Most patients are under 30 years of age.
• Local pain over the affected vertebrae - the most common early symptom; worsens with activity.
• Pain referred along spinal nerves may mimic neuralgia, sciatica, or abdominal pathology.
• Night cries in children (pain due to muscle relaxation during sleep).
• Paraspinal muscle spasm, restricted movements.
• Kyphosis (gibbus) - visible localised angular kyphosis in the dorsal spine in advanced cases.
• Cold abscess features: dysphagia, dyspnoea (retropharyngeal abscess), flexion deformity of hip (psoas abscess).

Radiological Features

• Takes 3-5 months for bony destruction to appear on plain X-ray; >30% of mineral must be lost.
• Paradiscal type (most common): Demineralisation with indistinct bony margins, narrowing of disc space, vertebral wedging.
• Central type: Lytic lesion in the vertebral body centre, ballooning - mimics tumour or Calve's disease.
• Anterior type: Shallow excavation on anterior/lateral surface.
• Fusiform paravertebral abscess shadow in thoracic spine; psoas shadow enlargement in lumbar.
• Skip lesions on X-ray.
• CT and MRI: Allow early identification of bony lesions, prevertebral/paravertebral abscess, and cord compression status.
• Severity of gibbus predicted by: y = a + bx (a = 5.5, b = 30.5, x = initial vertebral height loss).

Pott's Paraplegia

1. Smallest diameter of spinal canal in this region.
2. Abscess remains confined under tension and enters the spinal canal.
3. TB infection is common here.
4. Spinal cord terminates below L1.

Types

• Early onset paraplegia: During active disease - due to cold abscess, caseous material, granulation tissue, TB pus. Prognosis favourable.
• Late onset paraplegia: Years after disease becomes quiescent - due to internal gibbus, kyphotic deformity, dural fibrosis, spinal canal stenosis. Prognosis less favourable.

Mechanisms (Table 19.1)

• Extrinsic/mechanical (during active disease): Cold abscess, granulation tissue, sequestrated bone/disc fragments, pathological subluxation/dislocation.
• Following healing: Ridge of bone anterior to cord, fibrosis of dura mater, gliosis of cord.
• Intrinsic/non-mechanical: Spread of TB inflammation through dura to cord.
• Rare: Spinal tumour syndrome, thrombosis of anterior spinal artery.

Clinical Progression

Grading of Paraplegia

Differential Diagnosis

• Developmental: hemivertebra, Calve's disease, Schmorl's nodes, Scheuermann's disease.
• Infections: pyogenic osteomyelitis, brucellosis, enteric fever, mycotic infections.
• Benign neoplasms: haemangioma, aneurysmal bone cyst, giant cell tumour.
• Malignant: Ewing's tumour, chordoma, osteosarcoma, multiple myeloma, lymphoma, secondaries.
• Others: Paget's disease, traumatic fracture, hydatid disease, Langerhans cell histiocytosis.

Management

Anti-TB Treatment

• Essentially the same as pulmonary TB.
• INDEX-TB Guidelines (India): 2-month intensive phase (HRZE) + 10-16 months continuation phase (HRE) depending on disease site and clinical course.
• DOTS under RNTCP ensures compliance.
• Short-course treatment (9 months) has been shown equally effective in early, drug-susceptible disease.

Indications for Surgery (regardless of paraplegia)

• Doubtful diagnosis requiring open biopsy.
• Failure to respond to anti-TB drugs.
• Radiological progression of bony lesion or paraspinal abscess.
• Imminent vertebral collapse.
• Prevention of severe kyphosis.
• Spinal instability/subluxation/dislocation.

Surgical Options

• Anterolateral decompression with interbody bone grafting or costotransversectomy.
• Titanium cage filled with cancellous bone grafts when most of vertebral body is removed.
• Posterior spinal fusion (Hibbs and Albee methods) - now rarely used; reserved for junctional areas and children at risk of severe kyphosis.

Cold Abscess - Management

• Small abscess: heals with anti-TB treatment.
• Large/tense abscess: surgical drainage by appropriate approach.
• Paravertebral abscess: evacuated at time of bony debridement.

Treatment of Pott's Paraplegia - Three Schools

1. Immediate radical anterior debridement + decompression + arthrodesis in all cases (rationale: TB can penetrate dura, making recovery impossible if delayed).
2. Initial conservative treatment (immobilisation/bedrest); surgery only if no improvement within specified time.
3. Middle path regimen: Rest + anti-TB for 4 weeks; surgical decompression if no neurological improvement (recommended for developing countries with limited resources).

Key Examination Points to Remember

• Most common form of skeletal TB.
• L1 and lower thoracic are most commonly involved.
• Paradiscal is the most common radiological type.
• Psoas abscess = hallmark of lumbar Pott's disease.
• Pott's paraplegia in up to 30% - graded I-IV.
• Gibbus = angular kyphosis from vertebral collapse.
• MRI is the investigation of choice for early detection and cord assessment.
• INDEX-TB treatment duration: 12-18 months total for spinal TB.
• Middle path regimen is the practical approach in resource-limited settings.

Note: The PDF you attached is the Textbook of Tuberculosis and Nontuberculous Mycobacterial Diseases by Surendra K. Sharma & Mohan. The topic "Ponseti's disease" does not exist in this textbook. This answer is based on Pott's disease (Spinal TB) from Chapter 19 (pages 268-291 of the textbook), which is the relevant MD exam topic in this context. If you meant Ponseti's method (clubfoot treatment), that would require an orthopedic surgery textbook, not this one.