A 28-year-old woman presents with intense pruritus, worse at night, affecting her hands, wrists, and intertriginous areas for the past 3 weeks. Examination reveals linear burrows on the volar surface of wrists and between fingers, along with erythematous papules and excoriations. Her 5-year-old daughter and husband also have similar symptoms. Dermoscopy shows a triangular opacity at the end of a burrow. What is the most likely diagnosis?

## Clinical Diagnosis of Scabies ### Key Clinical Features **Key Point:** Scabies is a contagious parasitic infestation caused by *Sarcoptes scabiei* var. hominis, characterized by pathognomonic burrows and intense pruritus worse at night. ### Diagnostic Hallmarks Present in This Case | Feature | Finding in Case | Significance | |---------|-----------------|-------------| | **Burrows** | Linear, on volar wrists and finger webs | Pathognomonic; created by gravid female mite | | **Distribution** | Hands, wrists, intertriginous areas | Classic sites in adults | | **Pruritus** | Intense, nocturnal | Immune response to mite antigens | | **Dermoscopy** | Triangular opacity (mite) at burrow end | Confirmatory finding; "delta wing" or "jet with contrail" sign | | **Epidemiology** | Family involvement (daughter, husband) | Highly contagious; close contact transmission | | **Duration** | 3 weeks | Consistent with primary infestation timeline | ### Pathophysiology 1. Gravid female mite burrows into stratum corneum 2. Lays 2–3 eggs daily; burrow extends 1–10 mm 3. Immune response (Th2-mediated) → pruritus and papules 4. Secondary excoriations and bacterial superinfection common ### High-Yield Diagnostic Criteria **High-Yield:** The combination of **burrows + nocturnal pruritus + family involvement** is virtually diagnostic of scabies. Dermoscopic visualization of the mite clinches the diagnosis. **Mnemonic: BURROW** — **B**urrows on hands/wrists, **U**nder skin, **R**ed papules, **R**ough excoriations, **O**wn and others affected, **W**orse at night ### Confirmatory Methods - **Dermoscopy** (as done here): Mite, eggs, feces visible as triangular or comma-shaped opacities - **Scabies preparation (KOH mount):** Burrow material scraped, mounted; mite/eggs/feces visible - **Ink test:** Burrow traced with ink; mite at end absorbs ink **Clinical Pearl:** Absence of burrows does NOT exclude scabies—in nodular scabies or crusted scabies (immunocompromised), burrows may be absent or atypical. ### Treatment Overview - **First-line:** Permethrin 5% cream (apply neck to toe, 8–14 hours, repeat after 1 week) - **Oral ivermectin:** For crusted scabies, institutional outbreaks, or patient preference - **Household/close contacts:** Treat simultaneously regardless of symptoms - **Fomites:** Wash bedding, clothing in hot water; vacuum furniture [cite:Fitzpatrick's Dermatology 9e Ch 24]