A 42-year-old woman presents with thoracic back pain and progressive paraplegia over 6 months. MRI shows T6–T8 vertebral destruction with kyphosis and epidural involvement. Which finding best distinguishes Pott disease from metastatic spinal disease in this scenario?

## Distinguishing Feature: Skip Lesions and Non-Contiguous Involvement **Key Point:** The pattern of vertebral involvement—particularly skip lesions (non-contiguous affected vertebrae)—is the key discriminator between Pott disease and metastatic disease. ### Comparison Table | Feature | Pott Disease (TB) | Metastatic Spinal Disease | |---------|-------------------|---------------------------| | **Vertebral involvement pattern** | **Multiple, often non-contiguous (skip lesions)** | **Usually contiguous or random scattered** | | **Number of vertebrae** | 2–3 or more (often skip pattern) | Variable, often multiple | | **Anterior vertebral body** | Preferentially involved | May involve any region | | **Epidural involvement** | Common (from granulation tissue) | Common (from tumor extension) | | **Kyphosis** | Progressive, severe | Variable | | **Paravertebral abscess** | Characteristic (cold abscess) | Absent | | **Primary tumor history** | Absent | Usually present | | **Age of presentation** | Younger (20–40 years) | Older (>50 years, variable) | ### Pathophysiology of Skip Lesions in Pott Disease 1. **Batson venous plexus spread:** TB spreads via valveless vertebral venous plexus 2. **Multiple seeding sites:** Infection seeds at multiple vertebral bodies simultaneously 3. **Non-contiguous pattern:** Lesions appear at different levels (T2, T5, T8, etc.) without involvement of intervening vertebrae 4. **Granulomatous spread:** TB spreads along ligaments and under the anterior longitudinal ligament, creating a characteristic pattern ### Metastatic Disease Spread - Usually **hematogenous** via systemic circulation - Tends to involve **contiguous or randomly scattered vertebrae** - Pattern depends on tumor type and vascular distribution - Skip lesions are **not characteristic** of metastatic disease **High-Yield:** Skip lesions (non-contiguous vertebral involvement) are pathognomonic for Pott disease. When you see multiple vertebrae involved with gaps between them on imaging, think TB first. **Clinical Pearl:** A patient with skip lesions + paravertebral soft tissue shadow (cold abscess) + insidious onset is virtually diagnostic of Pott disease. The absence of a known primary malignancy further supports TB. **Mnemonic:** **SKIP = TB** — Skip lesions indicate Pott disease; metastatic disease is usually contiguous or random. [cite:Robbins 10e Ch 8; Harrison 21e Ch 158]