Which radiological sign on plain radiography indicates early-stage Pott disease before significant vertebral collapse occurs?

Explanation

## Early Radiological Signs of Pott Disease **Key Point:** The **anterior vertebral body erosion** (lytic sign) is the earliest radiological manifestation of Pott disease, appearing before vertebral collapse develops. ### Progression of Radiological Findings | Stage | Radiological Finding | Timeline | |-------|----------------------|----------| | **Early (Stage 1)** | Anterior vertebral body erosion; loss of sharp anterior margin; osteopenia | 2–4 weeks | | **Active (Stage 2)** | Vertebral body collapse; disc space narrowing; kyphotic deformity begins | 6–12 weeks | | **Late (Stage 3)** | Gibbus deformity (severe kyphosis); paravertebral abscess (seen on CT/MRI); cord compression | Months to years | ### Why Anterior Erosion Occurs First? The anterior vertebral metaphysis is the primary site of tuberculous infection. Caseous necrosis and osteoclastic activity destroy the anterior cortex before the vertebral body loses height. This creates a characteristic **"moth-eaten" or "fuzzy" anterior margin** on lateral radiographs. **Clinical Pearl:** The **lytic sign** (erosion of the anterior vertebral margin) is often the ONLY finding on plain radiographs in early disease. MRI is far more sensitive for detecting early TB spondylitis before radiographic changes appear. **High-Yield:** Gibbus deformity is a LATE sign indicating advanced disease with significant vertebral collapse and kyphosis. It is NOT an early finding and should not be expected in Stage 1 disease. **Mnemonic:** **EARLY signs = Erosion, Late signs = Gibbus** - **E**rosion of anterior vertebral body → early - **L**ytic changes, **A**bscess (paravertebral) → intermediate - **T**otal collapse, **E**pidural extension → late - **G**ibbus deformity → very late [cite:Park 26e Ch 3]