## Distinguishing Scabies from Atopic Dermatitis ### Pathognomonic Feature of Scabies **Key Point:** Burrows (linear or S-shaped tunnels in the stratum corneum) are the pathognomonic finding of scabies and are virtually absent in atopic dermatitis. These are created by the gravid female mite as it tunnels through the epidermis. **High-Yield:** Burrows are most commonly found in: - Web spaces between fingers (classic location) - Flexor wrists - Palms and soles - Axillae - Genitalia - Inframammary fold ### Comparative Table: Scabies vs Atopic Dermatitis | Feature | Scabies | Atopic Dermatitis | | --- | --- | --- | | **Burrows** | Present (pathognomonic) | Absent | | **Lichenification** | Secondary (from scratching) | Primary finding | | **Xerosis** | Not prominent | Marked, primary | | **Seasonal pattern** | No clear seasonality | Winter exacerbation | | **Family history** | No genetic predisposition | Often positive (atopy) | | **Pruritus timing** | Nocturnal, worse at night | Variable, not specifically nocturnal | | **Response to topical scabicide** | Complete cure | Chronic relapsing course | ### Clinical Pearl **Clinical Pearl:** The presence of burrows with nocturnal pruritus in a patient with household contacts also affected strongly suggests scabies over atopic dermatitis. Dermoscopy or magnification can help visualize burrows when clinical diagnosis is uncertain. ### Diagnostic Confirmation Scabies diagnosis can be confirmed by: - Microscopy of burrow scrapings (mite, eggs, or feces) - Dermoscopy showing the mite at the burrow entrance - Skin biopsy (rarely needed) **Warning:** Do not confuse secondary lichenification in chronic scabies with primary lichenification of atopic dermatitis — the presence of burrows and positive scrapings will clarify the diagnosis. 
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