Which of the following is the most sensitive diagnostic method for confirming scabies in a patient with clinical suspicion?

Explanation

## Diagnosis of Scabies: Confirmatory Methods **Key Point:** Microscopic examination of burrow scrapings is the gold standard for confirming scabies; it demonstrates mites, eggs, or fecal pellets (scybala). ### Diagnostic Methods Comparison | Method | Sensitivity | Specificity | Procedure | Yield | | --- | --- | --- | --- | --- | | **Burrow scraping + microscopy** | 60–80% | 100% | Scrape burrow with scalpel; mount on slide ± KOH; examine for mites/eggs/feces | Gold standard | | **Dermoscopy** | 85–95% | High | Visualize mite, burrow structure, or "delta wing" sign | Non-invasive; increasingly used | | **KOH mount of scales** | 40–50% | High | Dissolve scale with KOH; examine for mites | Lower yield than burrow scraping | | **Wood's lamp** | Poor | Poor | No fluorescence in typical scabies | Not useful for diagnosis | | **Ink test** | Moderate | Moderate | Apply ink; wipe; burrows retain ink | Useful for teaching; not standard | ### Technique for Burrow Scraping 1. **Identify burrow:** Linear or S-shaped tunnel, typically on wrist, finger web, or axilla 2. **Scrape:** Use scalpel blade at 45° angle; scrape burrow and surrounding area until blood oozes slightly 3. **Mount:** Place scrapings on glass slide with mineral oil or KOH solution 4. **Examine:** Low power (×10) to locate mites; high power (×40) for detailed identification 5. **Findings:** Mites (oval, 0.3–0.4 mm), eggs, or fecal pellets (scybala) = positive **High-Yield:** Sensitivity is only 60–80% because not all burrows contain mites at the time of scraping. Multiple scrapings from different burrows increase diagnostic yield. **Clinical Pearl:** If clinical suspicion is high but microscopy is negative, treat empirically — the cost of missing scabies (continued transmission, complications) outweighs the risk of unnecessary treatment. **Mnemonic:** **SCABIES Diagnosis** — **S**craping from **C**linical **A**reas (burrows) **B**y **I**ncision **E**xamined under **S**cope (microscope). ### Why Other Methods Are Suboptimal - **Dermoscopy:** Highly sensitive and non-invasive; increasingly popular but requires dermoscope and expertise. Not universally available in all settings. - **KOH mount of scales:** Lower yield because mites preferentially live in burrows, not in loose scales - **Wood's lamp:** No diagnostic utility; scabies does not fluoresce