What is the most likely diagnosis and first‑line treatment for a patient with a thin, linear, serpiginous lesion on the leg that migrates over time?

Cutaneous Larva Migrans (Creeping Eruption)

Diagnosis

The most likely diagnosis is cutaneous larva migrans (CLM), a hookworm infection presenting as a characteristic serpiginous, linear skin lesion that migrates 1-2 cm per day. 1

• The diagnosis is made clinically based on the distinctive appearance of an erythematous, raised, serpentine track that advances progressively across the skin, combined with a history of potential exposure to contaminated soil or sand 1, 2
• The lesion is typically intensely pruritic (itchy), often severe enough to disrupt sleep 2, 3
• CLM is caused by penetration of dog or cat hookworm larvae (most commonly Ancylostoma braziliense or A. caninum) into human skin, where they remain trapped in the upper dermis and migrate without completing their life cycle 4, 3
• Laboratory confirmation is not required for diagnosis; the clinical presentation is sufficiently distinctive 1
• Peripheral eosinophilia may be present but is not necessary for diagnosis 1

First-Line Treatment

The recommended first-line treatment is either ivermectin 200 μg/kg as a single oral dose OR albendazole 400 mg once daily for 3 days. 1

Ivermectin (Preferred Single-Dose Option)

• Ivermectin 200 μg/kg (0.2 mg/kg) given as a single oral dose achieves cure rates approaching 95-100% 1, 5
• This is the most convenient option, requiring only one dose 1
• No dose adjustments are required for renal impairment, though safety of multiple doses in severe liver disease is not established 1

Albendazole (Alternative 3-Day Course)

• Albendazole 400 mg once daily for 3 days is equally effective with excellent tolerability 1, 2
• For patients with multiple or extensive lesions, extending treatment to 7 days may reduce recurrence rates, achieving 100% cure rates without increased side effects 1

Critical Clinical Pitfall

Do not confuse persistent itching with treatment failure. Pruritus can persist for several days after successful parasite eradication due to ongoing inflammatory and allergic dermatitis from dead larvae 1. This is a common source of unnecessary re-treatment.

Special Populations

• Pregnancy: Ivermectin has shown no teratogenicity in limited human data, though caution is warranted; albendazole should ideally be avoided, especially in the first trimester 1
• Breastfeeding: Both ivermectin and albendazole appear compatible with breastfeeding based on low excretion into breast milk 1

Key Differential Diagnoses to Exclude

• Erythema migrans (Lyme disease): This presents as a round or oval expanding erythematous lesion (not linear/serpiginous), typically ≥5 cm in diameter, appearing 7-14 days after tick bite 6
• Strongyloidiasis (larva currens): Presents with rapidly moving urticarial tracks on trunk, upper legs, and buttocks, migrating much faster than CLM 7
• Drug reaction: Generally non-migratory maculopapular eruptions without the characteristic winding, snake-like pattern of CLM 1

Prevention

• Avoid unprotected skin contact with soil or sand potentially contaminated with dog or cat feces 1, 2
• Proper hand hygiene after contact with dogs or potentially contaminated soil 1
• Wear protective footwear on beaches in endemic areas 2, 3