A rash that "traveled" over the top of the foot

A 47-year-old female presented to our dermatology clinic with a recent history of vacationing in Panama City, Florida. During her stay, she often walked in the sand without shoes. Three to four days after returning home, she developed small blisters, severe pruritus, erythema, and swelling on the right dorsal foot between the fourth and fifth toes. The patient thought she had poison ivy and treated the area with topical pramoxine (Caladryl) and oral diphenhydramine (Benadryl). She noticed that the rash “moved,” making a path across the top of her foot. A friend, who raised puppies, thought it might be a “hookworm” infection.

The patient was initially seen by a surgeon, who performed an ultrasound in the hopes of visualizing the hookworm and cutting it out. He was unable to see any infectious agent in the skin. He put her on cephalexin (Keflex) for any superficial infection from scratching and mebendazole (Vermox), 100 mg twice daily for 3 days. Her last dose was 3 days before presenting to our office.

The patient stated that the infection continued to migrate across the top of her foot and was now moving onto the medial and plantar aspect of the foot. She could feel something moving in her skin, it burned intensely, and the pruritus was an 8 to 9 on a scale of 10, with 10 being the worst itching she has ever felt. The burning sensation was usually several millimeters in advance of where the eruption could be seen (see Figure 1).

DISCUSSION

This patient has cutaneous larva migrans (CLM), which is the name for infection with dog hookworm when it occurs in humans. In human infection, the hookworm gains access to the epidermis but lacks the collagenase enzymes required to penetrate the human basement membrane and get into the dermis, as occurs with dogs; thus in humans, the larva is left forever “migrating” through the epidermis, creating the pathognomic serpiginous eruption known as CLM. The eruption is the result of an allergic reaction by the human host in response to the proteases produced by the migrating larvae. The larva usually begins to migrate about 4 days post-inoculation and proceeds at a rate of about 2 cm daily.

Infections occur in warm, moist, sandy areas where dogs defecate and their feces contain infectious larva that come into contact with human skin. Sandboxes; beneath buildings where plumbers, electricians, and pest exterminators work; and public beaches (most commonly in Florida and Georgia in the southeastern United States) are common sites where infection can occur.

Treatment CLM is considered a selflimiting condition (lasting 4-8 weeks), but the intense pruritus and burning require symptomatic relief.

Today broad-spectrum antihelminthics can be used, but thiobendazole is considered the drug of choice. It is not very well-tolerated by mouth and is best used when compounded into a cream and applied 3 to 4 times daily to the affected areas and about 2 to 3 cm in advance of the most recent tract. Symptomatic relief can be obtained in about 48 hours.

A more tolerable oral treatment is ivermectin (Stromectol), which has minimal toxicity and is available in a single dose, enhancing adherence. We chose to treat the patient with compounded thiobendazole in Cetaphil cream and a single oral 12-mg dose of ivermectin. The patient returned to our office in 1 week; symptoms had resolved, and the eruption was beginning to clear by at least 50%. JAAPA

Sandra Morris practices in general dermatology. Steven Marcet practices in general dermatology and is a Mohs surgeon. Both work at Newnan Dermatology, Newnan, Georgia. The authors have indicated no relationships to disclose relating to the content of this article.