A 28-year-old woman presents with intense itching for 3 weeks, worse at night. She reports burrows on her wrists, finger webs, and axillae. Her 5-year-old daughter and husband also have similar symptoms. Examination reveals erythematous papules, excoriations, and characteristic linear burrows. Dermoscopy shows the mite, eggs, and feces within the burrow. What is the most appropriate first-line treatment?

Explanation

## Diagnosis & Clinical Context **Key Point:** Scabies is a contagious parasitic infestation caused by *Sarcoptes scabiei* var. hominis. The classic presentation includes nocturnal pruritus, burrows on characteristic sites (finger webs, wrists, axillae, genitalia), and household transmission. ## First-Line Treatment in India **High-Yield:** Permethrin 5% cream is the gold-standard first-line treatment in most guidelines, including those followed in Indian dermatology practice. | Feature | Permethrin 5% | Sulfur 5% | Ivermectin | Benzyl Benzoate | |---------|---------------|-----------|-----------|------------------| | **Mechanism** | Neurotoxin (sodium channel blockade) | Scabicidal | Antiparasitic (GABA agonist) | Scabicidal | | **Application** | Single application, repeat after 7 days | Daily for 7 days | Oral, 2 doses 1–2 weeks apart | 3 consecutive nights | | **Pregnancy** | Safe (Category B) | Safe | Contraindicated | Safe | | **Age** | Safe from 2 months | Safe from birth | Avoid <15 kg | Safe from 6 months | | **Compliance** | Excellent (2 applications) | Poor (7 applications) | Excellent (oral) | Moderate (3 nights) | | **Cost** | Moderate | Low | High | Low | **Clinical Pearl:** The 7-day interval between permethrin applications allows for killing of newly hatched mites from eggs that survive the first application. ## Management of Household Contacts **Key Point:** All household members and close contacts must be treated simultaneously, regardless of symptoms, as the incubation period is 2–6 weeks. ## Application Technique (Permethrin) 1. Apply to entire body surface from neck downward 2. Pay special attention to finger webs, wrists, axillae, inframammary folds, genitalia, and buttocks 3. Leave on for 8–14 hours (usually overnight) 4. Wash off thoroughly 5. Repeat after 7 days **Tip:** Advise patients to trim fingernails short before application to reduce mite harboring under nails. ## Post-Treatment Pruritus **Warning:** Itching may persist for 2–4 weeks after successful treatment due to residual inflammation and mite antigens. This does NOT indicate treatment failure. Topical corticosteroids or antihistamines can be used for symptomatic relief. ## Fomite Management **Key Point:** Clothing, bedding, and towels should be washed in hot water (>60°C) or sealed in a plastic bag for 7 days to kill mites. [cite:Park 26e Ch 8]