## Pathognomonic Sign of Scabies: The Burrow **Key Point:** The scabies burrow is the diagnostic hallmark of scabies and represents the tunnel created by the gravid female mite in the stratum corneum. ### Burrow Characteristics | Feature | Description | |---------|-------------| | **Appearance** | Linear, S-shaped, or zigzag tract | | **Length** | 5–15 mm typically | | **Colour** | Skin-coloured or slightly erythematous | | **Visibility** | May be difficult to see; use magnification or dermoscopy | | **Location** | Interdigital spaces, wrists, elbows, axillae, genitalia, buttocks | | **Pathology** | Female mite visible at burrow end under magnification | **High-Yield:** The burrow is the only lesion pathognomonic for scabies; all other lesions (papules, vesicles, pustules, excoriations) are secondary to scratching or host inflammatory response. ### Clinical Presentation Beyond Burrows - **Primary lesions:** Burrows (pathognomonic) - **Secondary lesions:** Papules, nodules, vesicles, pustules, crusts (from scratching and superinfection) - **Pruritus:** Intense, worse at night; often out of proportion to visible lesions **Clinical Pearl:** In immunocompromised patients (HIV/AIDS), crusted scabies (Norwegian scabies) may develop with minimal burrows but extensive hyperkeratotic crusting and high mite burden. ### Diagnostic Confirmation 1. **Dermoscopy:** Visualizes burrow and mite 2. **Scrapings:** Mite, eggs, or faeces seen under microscopy 3. **Ink test:** Burrow highlighted with ink for visualization 4. **Histopathology:** Mite in stratum corneum (rarely needed) [cite:Park 26e Ch 3] 
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