A 13-year-old boy is brought to the surgery complaining of intense itching over the lateral border of his left foot. He is otherwise well.
On examination, there is a readily visible, raised 2mm wide elongated track with surrounding erythema. On questioning, his mother says they had been in Florida three weeks ago. What is the diagnosis, management and differential diagnosis?
Diagnosis and management
The diagnosis is cutaneous larva migrans, which is a parasitic skin infection acquired in the tropics or sub-tropics and occurring on exposed areas of skin. It is caused by the larva of a hookworm, most commonly that of Ancylostoma braziliensis or Ancylostoma caninum which is excreted in the faeces of dogs, cats or other creatures and which enters the body and is then unable to escape.
The rash is commonly seen on feet, arms or buttocks. A sharp intense pain may be felt when it enters the skin, but the rash and prolonged pruritus occur from one week to several months after the initial penetration as it migrates under the skin causing the characteristic serpiginous track. The pruritus is due to an allergic immune response to the larva.
The rate of migration can vary from 2–20mm daily, according to the larva species. Treatment is with an antihelmintic such as mebendazole 100mg twice daily for three days, especially if the rash is particularly itchy.
Possible different diagnoses
- Lyme disease — erythema chronicum migrans.
- Sting by jellyfish.
- Transmitted by ticks.
- Red macule or papule on arm, leg, or trunk.
- Lesions can be up to 50cm in diameter.
- Smaller lesions found elsewhere.
- Lymphodenopathy may be a feature.
- Treatment is usually with doxycycline or erythromycin.
Contributed by Dr Gwen Lewis, a GP in Windsor, Berkshire