A 32-year-old woman presents with intense pruritus, particularly worse at night, affecting her wrists, interdigital spaces, and lower abdomen for the past 3 weeks. She reports that her 6-year-old daughter and husband have developed similar symptoms. On examination, you observe linear burrows on the volar aspect of the wrists and between the fingers. Dermoscopy reveals the characteristic 'jet with a trail' sign. What is the most appropriate first-line treatment for this patient and her family?

Explanation

## Diagnosis & Clinical Features **Key Point:** The clinical presentation of nocturnal pruritus, burrows in characteristic sites (wrists, interdigital spaces, genitalia, lower abdomen), and the 'jet with a trail' sign on dermoscopy are pathognomonic for scabies. **Clinical Pearl:** The involvement of family members (daughter and husband) confirms the contagious nature of scabies and indicates household transmission — all contacts must be treated simultaneously to prevent reinfection. ## First-Line Treatment **High-Yield:** Permethrin 5% cream is the gold-standard first-line treatment for scabies in adults and children >2 months of age. ### Permethrin 5% Cream — Standard Protocol | Feature | Details | |---------|----------| | **Concentration** | 5% | | **Application** | Full-body application from neck downward | | **Duration per application** | 8–14 hours (overnight application preferred) | | **Dosing schedule** | Apply once, repeat after 7 days | | **Mechanism** | Neurotoxin to mites; disrupts sodium channel function | | **Efficacy** | >95% cure rate with two applications | | **Safety** | Safe in pregnancy and children >2 months | **Key Point:** Two applications 1 week apart are essential because the first application kills adult mites and nymphs but may not reliably kill eggs; the second application targets mites that hatch from surviving eggs. ## Why Simultaneous Family Treatment Is Mandatory 1. Scabies is highly contagious (transmission occurs with 15–20 minutes of skin-to-skin contact). 2. Incubation period is 2–6 weeks; asymptomatic carriers can transmit. 3. Treating only the index patient will result in reinfection from untreated household contacts. 4. All family members should apply permethrin on the same day. ## Adjunctive Measures - Wash all bedding, towels, and clothing in hot water (>50°C) or seal in plastic bags for 72 hours (mites cannot survive >3 days off skin). - Treat close contacts (sexual partners, household members) even if asymptomatic. - Pruritus may persist for 2–4 weeks after successful treatment due to residual inflammation; use topical corticosteroids or antihistamines for symptomatic relief. **Mnemonic:** **PERMETHRIN** = **P**erfect for **E**very **R**elative (treat all), **M**ites **E**radicated, **T**wice in **H**istory (two doses), **R**epeat at **I**nterval of 7 days, **I**ncredibly **N**on-toxic. [cite:Irvine's Dermatology 10e Ch 24]