A 28-year-old man with suspected scabies presents with severe pruritus and widespread erythematous papules. Clinical examination shows burrows on the hands and feet. Skin scrapings for KOH mount are negative. Which is the most appropriate next investigation to confirm the diagnosis?

Explanation

## Next Best Investigation After Negative KOH Mount **Key Point:** Dermoscopy is the most appropriate next investigation when KOH mount is negative but clinical suspicion remains high, because it has superior sensitivity (95–98%) and can visualize the mite in situ without tissue destruction. ### Why Dermoscopy is Superior to Repeat KOH 1. **Higher sensitivity** — 95–98% vs. 60–80% for KOH 2. **Non-invasive visualization** — allows direct in vivo observation of mite, burrows, and characteristic features 3. **Rapid and repeatable** — can examine multiple sites without damage 4. **Identifies diagnostic patterns:** - **"Mite" or "delta wing" sign** — the mite body with front legs - **"Triangular sign"** — anterior end of mite - **"Jet with contrail" sign** — mite with burrow trail ### Dermoscopic Features of Scabies | Feature | Description | Specificity | | --- | --- | --- | | Mite (delta wing sign) | Triangular or comma-shaped structure | Pathognomonic | | Burrow | Linear or S-shaped track | Highly specific | | Eggs | Small dots in burrow | Specific | | Fecal pellets | Brown dots along burrow | Specific | **High-Yield:** Dermoscopy is increasingly recognized as the **non-invasive gold standard** for scabies diagnosis, especially in resource-rich settings and when KOH is negative. **Clinical Pearl:** Dermoscopy is particularly useful in **atypical scabies** (nodular, bullous, or incognito variants) where mite burden may be low and KOH sensitivity is reduced.