A 38-year-old man from rural Madhya Pradesh presents with a 6-month history of progressive back pain and lower limb weakness. On examination, he has kyphotic deformity of the thoracic spine, paraparesis (grade 3/5 bilaterally), and a sensory level at T8. Plain radiographs show anterior vertebral body collapse with loss of disc space height at T6–T7, and MRI reveals heterogeneous signal intensity in the vertebral bodies with epidural extension compressing the spinal cord. Tuberculin skin test is positive (18 mm induration). What is the most likely diagnosis and the primary mechanism of neurological deficit in this patient?

Explanation

## Diagnosis: Pott Disease (Spinal Tuberculosis) **Key Point:** Pott disease is tuberculosis of the spine, most commonly affecting the thoracic and lumbar vertebrae. It is the most common form of skeletal tuberculosis and remains endemic in India. **Clinical Features Supporting Diagnosis:** - Insidious onset over months (typical of TB; acute pyogenic infections present acutely) - Kyphotic deformity ("gibbus" deformity) from anterior vertebral body collapse - Positive tuberculin skin test (TST ≥15 mm is significant in endemic areas) - MRI findings: heterogeneous signal, vertebral body involvement with disc space involvement - Paraparesis with sensory level indicating spinal cord compression ## Mechanism of Neurological Deficit **High-Yield:** Spinal cord compression in Pott disease occurs through multiple mechanisms: 1. **Epidural granulation tissue and abscess** — most common cause of acute/subacute cord compression 2. **Vertebral collapse and kyphotic deformity** — mechanical compression from bone destruction 3. **Instability and subluxation** — from loss of vertebral body integrity 4. **Fibrosis and adhesions** — late mechanism causing chronic myelopathy **Clinical Pearl:** The epidural space is involved in ~50% of Pott disease cases. Granulation tissue, caseous material, and abscess formation in the epidural space are the PRIMARY reversible causes of cord compression and are amenable to anti-TB therapy and decompression if needed. ## Imaging Findings in Pott Disease | Feature | Pott Disease | Pyogenic Osteomyelitis | Metastatic Tumour | |---------|--------------|----------------------|-------------------| | **Onset** | Insidious (weeks–months) | Acute (days–weeks) | Variable | | **Vertebral involvement** | Anterior body (paradiscal) | Central or posterior | Variable | | **Disc space** | Early involvement (TB crosses disc) | Spared initially | Usually spared | | **Kyphosis** | Common (gibbus) | Rare | Rare | | **TST/Culture** | Positive TB culture/PCR | Blood/CSF culture positive | Negative | | **Epidural involvement** | Common (granulation tissue) | Common (pus/abscess) | Common (tumour) | **Key Point:** In Pott disease, TB crosses the disc space early (unlike pyogenic infections), leading to involvement of adjacent vertebral bodies and characteristic "skip lesions."