What is the assessment and treatment plan for scabies?

Assessment and Management of Scabies

Diagnosis

Confirm scabies by identifying burrows, papules, vesicles, and excoriations in characteristic distributions: finger webs, wrists, axillary folds, abdomen, buttocks, inframammary folds, and male genitalia. 1

• Look for intense nocturnal pruritus as a key clinical feature 1
• In infants and elderly patients, check the scalp, hairline, neck, temple, and forehead, which are typically spared in adults 2
• Definitive diagnosis requires microscopic identification of mites, eggs, or fecal pellets from skin scrapings 1
• Epiluminescence microscopy (dermoscopy) can be used as a newer diagnostic technique 1

First-Line Treatment

Permethrin 5% cream is the FDA-approved and guideline-recommended first-line treatment for uncomplicated scabies. 3, 4, 2

Permethrin Application Protocol

• Apply to all areas of the body from neck down (include scalp, temple, and forehead in infants and elderly) 2
• Leave on for 8-14 hours, then wash off 3, 2
• Use approximately 30 grams for an average adult 2
• One application is generally curative 2
• Repeat treatment after 7-10 days if symptoms persist or live mites are observed after 14 days 3, 2

However, a critical 2024 study found only 27% cure rate with permethrin vs. 87% with benzyl benzoate, suggesting emerging resistance. 5 This challenges the traditional first-line status of permethrin in some populations.

Oral Ivermectin Alternative

• Dose: 200 μg/kg body weight, repeated in 2 weeks 3, 4
• Take with food to increase bioavailability 3, 4
• Particularly useful for institutional outbreaks, immunocompromised patients, and treatment failures 1
• Single dose provides 62-86% cure rate; two doses achieve 93-100% cure 6, 7

Special Populations

Pregnant and Lactating Women

Use permethrin 5% cream exclusively—avoid lindane and consider ivermectin only if benefits outweigh risks. 3, 4

Infants and Children

• Permethrin 5% is preferred 3
• Apply to scalp, temple, and forehead in addition to body 2
• Never use lindane in children <10 years due to neurotoxicity risk 3, 4

Immunocompromised Patients

These patients are at high risk for crusted (Norwegian) scabies requiring aggressive combination therapy. 3, 4

Crusted (Norwegian) Scabies

Requires combination therapy: permethrin 5% cream applied daily for 7 days, then twice weekly until cure, PLUS oral ivermectin 200 μg/kg on days 1,2,8,9, and 15. 3, 4

• Single-agent therapy will fail due to massive mite burden (thousands to millions of mites) 4
• Never use lindane in this population due to increased absorption through damaged skin 4
• Consult an expert for management 3

Environmental and Contact Management

Treat all sexual, close personal, and household contacts within the preceding month simultaneously, even if asymptomatic. 3, 4

Decontamination Protocol

• Machine wash and dry bedding/clothing on hot cycle 3, 4
• Alternatively, dry-clean or remove items from body contact for at least 72 hours 3, 4
• Fumigation of living areas is unnecessary 3, 4
• Trim fingernails closely to reduce scratching injury 3

Follow-Up and Expected Course

Pruritus may persist for up to 2 weeks after successful treatment and does NOT indicate treatment failure. 3, 4, 2

Indications for Retreatment

• Live mites observed after 14 days 2
• Symptoms persisting beyond 2 weeks 3, 4
• New lesions appearing after initial improvement 3

Common Causes of Treatment Failure

• Failure to treat all close contacts simultaneously 3, 4
• Inadequate application of topical treatment (missing body areas) 3, 4
• Not repeating ivermectin dose after 2 weeks 3, 4
• Reinfection from untreated contacts or contaminated fomites 4
• Emerging permethrin resistance 5

Alternative Treatments

When Permethrin Fails or Is Unavailable

• Benzyl benzoate 25%: Recent evidence shows 87% cure rate vs. 27% for permethrin, though causes burning sensation in 43% of patients 5
• Lindane 1%: Apply thinly from neck down, wash off after 8 hours—contraindicated in children <10 years, pregnant/lactating women, and persons with extensive dermatitis 8, 3, 4
• Sulfur 6% ointment: Apply nightly for 3 nights 3
• Crotamiton 10%: Apply nightly for 2 consecutive nights, wash off 24 hours after second application 8

Critical Pitfalls to Avoid

• Using lindane after bathing (increases absorption and seizure risk) 8, 3
• Expecting immediate symptom resolution (itching persists 1-2 weeks normally) 3, 2
• Treating only the index patient without treating contacts 3, 4
• Applying topical treatment only to visible lesions rather than entire body 3, 4