A 32-year-old woman presents with intense pruritus, particularly worse at night, for the past 3 weeks. She reports burrows on her wrists, interdigital spaces, and lower abdomen. Her 6-year-old daughter and husband also have similar symptoms. On dermoscopy, a characteristic 'jet with a trail' sign is noted. What is the most appropriate first-line treatment for this patient and her family?

Explanation

## Diagnosis and Clinical Context **Key Point:** The clinical presentation of nocturnal pruritus, burrows in characteristic sites (wrists, interdigital spaces, abdomen), and dermoscopic finding of the 'jet with a trail' sign (mite with its burrow) are pathognomonic for scabies. **High-Yield:** Scabies is a contagious parasitic infestation caused by *Sarcoptes scabiei* var. hominis. The entire household must be treated simultaneously to prevent re-infestation. ## Treatment Algorithm ```mermaid flowchart TD A[Confirmed Scabies]:::outcome --> B{Patient type?}:::decision B -->|Adult/Child >2 yrs| C[Permethrin 5% cream]:::action B -->|Infant <2 yrs or pregnant| D[Sulfur 5-10% ointment]:::action B -->|Severe/Crusted| E[Ivermectin + topical agent]:::action C --> F[Apply neck down, repeat day 7]:::action D --> G[Apply for 3 consecutive nights]:::action E --> H[Oral ivermectin + permethrin]:::action F --> I[Treat all household contacts]:::action G --> I H --> I I --> J[Symptomatic relief: antihistamines]:::action ``` ## Why Permethrin 5% is First-Line | Feature | Permethrin 5% | Benzyl Benzoate | Sulfur 5% | Ivermectin | |---------|---------------|-----------------|-----------|------------| | **Efficacy** | 95% (single application) | 90% | 85% | 90% | | **Age** | >2 months | All ages | Preferred <2 yrs | >15 kg only | | **Pregnancy** | Safe (Category B) | Caution | Preferred | Contraindicated | | **Application** | 2 applications, 7 days apart | Single application, wash after 24 hrs | 3 nights consecutive | Oral, repeat after 7 days | | **Tolerability** | Excellent | Irritant, odor | Messy, greasy | Systemic option | | **Cost** | Moderate | Low | Low | High | **Clinical Pearl:** Permethrin is neurotoxic to mites but safe in humans due to rapid skin metabolism. It is the WHO-recommended first-line agent for scabies in non-pregnant adults and children >2 months. **High-Yield:** The application must cover the entire body from neck downward, including web spaces, genitals, and buttocks. Many treatment failures occur due to inadequate application or failure to treat contacts. ## Management of Contacts and Fomites **Key Point:** All household members and close contacts must receive simultaneous treatment, regardless of symptoms, as the incubation period is 2–6 weeks. - Wash all bedding, clothing, and towels in hot water (>60°C) or seal in plastic bags for 7 days - Non-washable items (pillows, mattresses) should be vacuumed or left unused for 1 week - Symptomatic relief: antihistamines (cetirizine 10 mg daily) and topical emollients - Pruritus may persist for 2–4 weeks even after successful treatment due to mite antigen-induced inflammation **Mnemonic:** **SCABIES** = **S**kin burrows, **C**ontacts treated, **A**pply permethrin, **B**ody coverage complete, **I**nterdigital spaces, **E**very 7 days repeat, **S**ymptomatic relief ## Why Other Options Are Suboptimal - **Benzyl benzoate:** Older agent, more irritant, requires single application but less convenient; reserved for resource-limited settings - **Sulfur 5%:** Preferred in infants <2 years and pregnant women, but less effective and requires 3 consecutive nights of application - **Ivermectin:** Reserved for crusted scabies, immunocompromised patients, or when topical agents fail; not first-line for uncomplicated scabies