A 28-year-old woman presents to the dermatology clinic with a 3-week history of intense pruritus, particularly worse at night. Examination reveals linear burrows on the finger webs, volar wrists, and axillae. She also has excoriated papules on the buttocks and genitalia. Her 5-year-old son and husband have similar symptoms. Dermoscopy of a burrow shows a triangular mite with eggs. What is the most appropriate immediate management?

Explanation

## Diagnosis and Clinical Features **Key Point:** The clinical presentation of linear burrows on characteristic sites (finger webs, wrists, axillae) combined with nocturnal pruritus and dermoscopic confirmation of the mite is pathognomonic for scabies. **High-Yield:** Scabies is a contagious infestation caused by *Sarcoptes scabiei var. hominis*. The burrow is the diagnostic hallmark — a linear or S-shaped tunnel created by the gravid female mite. ## Management Algorithm ```mermaid flowchart TD A[Confirmed scabies diagnosis]:::outcome --> B{Patient type?}:::decision B -->|Adult/child >2 years| C[Permethrin 5% cream]:::action B -->|Infant, pregnant, or contraindication| D[Sulfur 5-10% ointment]:::action B -->|Crusted scabies or systemic option needed| E[Ivermectin 200 µg/kg]:::action C --> F[Apply to entire body surface<br/>Repeat after 7 days]:::action D --> G[Apply daily for 5-7 days]:::action E --> H[Repeat dose at 2 weeks]:::action F --> I[Treat all household/sexual contacts]:::action G --> I E --> I ``` ## Why Permethrin 5% is the First-Line Choice | Feature | Permethrin 5% | Ivermectin | Sulfur 5% | Albendazole | |---------|---|---|---|---| | **First-line for non-crusted scabies** | ✓ | ✗ | ✗ | ✗ | | **Application** | Topical, entire body | Oral | Topical, entire body | Oral | | **Repeat dosing** | Day 7 | Week 2 | Daily × 5–7 days | Not standard | | **Safe in pregnancy** | Minimal systemic absorption | Contraindicated | ✓ | Contraindicated | | **Safe in infants** | >2 months | >15 kg or >5 years | ✓ from birth | Not standard | | **Cost-effective** | ✓ | Expensive | ✓ | Not indicated | **Clinical Pearl:** Permethrin must be applied to the **entire body surface**, including scalp, ears, neck, and intertriginous areas — not just visible lesions. A common error is applying only to affected areas, leading to treatment failure. ## Essential Management Points 1. **Timing of repeat application:** Permethrin is repeated 7 days later because it does not reliably kill eggs; the second application targets newly hatched mites. 2. **Household and sexual contacts:** All household members and sexual partners must be treated simultaneously, regardless of symptoms, to prevent reinfection. 3. **Decontamination:** Clothing, bedding, and fomites should be washed in hot water or isolated for 72 hours (mites cannot survive off-host >3 days). 4. **Pruritus management:** Antihistamines and topical corticosteroids may be needed; pruritus can persist for 2–4 weeks post-treatment due to residual mite antigens. **High-Yield:** Ivermectin is reserved for crusted (Norwegian) scabies, immunocompromised patients, or when topical application is impractical. It is NOT first-line for uncomplicated scabies in an immunocompetent patient. **Warning:** Sulfur 5% is safe in infants and pregnancy but is cosmetically unacceptable and messy; permethrin is preferred if age/pregnancy permits. **Mnemonic — SCABIES Management (First-line):** **S**ulfur (infants/pregnancy) | **C**reamPermethrin 5% (standard) | **A**bendazole (not used) | **B**enzoate (historical, rarely used) | **I**vermectin (crusted/systemic) | **E**xcoriation (treat secondary infection) | **S**ymptomatic contacts (treat all).