A 25-year-old woman presented with a one-month history of a pruritic eruption on the buttocks (see the accompanying figure). She had recently returned from a beach vacation in Mexico. She was given a methylprednisolone dose pack during a visit to the emergency department, but the eruption showed no improvement after one week.
The answer is D: cutaneous larva migrans. Cutaneous larva migrans, also known as creeping eruption, is a common, self-limited, parasitic infection often seen in patients who have recently traveled to tropical regions, particularly if they have frequented beaches and shady areas.1 Although it may be caused by a myriad of nematodes, the most common infective agent is a dog and cat hookworm, Ancylostoma caninum and Ancylostoma braziliense.2
The lesions of contact dermatitis occasionally may be serpiginous if the patient has brushed against the leaves of a poison ivy plant. A month-long duration would be uncommon, though, as is the intradermal nature of these lesions. Contact dermatitis typically involves superficial eczematous changes with bullae formation in advanced cases.
The lesions of tinea corporis often have well-demarcated, erythematous papules within the plaques, mimicking folliculitis. As in folliculitis, there are no serpiginous tracks in tinea corporis.
In folliculitis, patients have erythematous papules without the serpiginous tracks.
Urticaria may present with serpiginous lesions. However, the lesions are transient, lasting less than 24 hours in a given location on the skin.
Familial outbreaks of cutaneous larva migrans have been seen in which infection began with the household pet. When the animal defecates, the hookworms are shed and the larvae are picked up by humans through breaks in the skin, hair follicles and even through intact skin. The areas most often affected include the feet, hands, buttocks, thighs and chest.
The eruption begins as a pruritic reaction at the site of entry that progresses within a few hours into an inflamed papular or papulovesicular eruption. Tracks left by the larvae's migration may also be seen. The eruption may spread up to 1 to 2 cm per day. Severe pruritus, vesicular and bullous lesions, local swelling, erosions and folliculitis may also be encountered, especially in those with previous exposure. Biopsy is generally not helpful and blood tests only rarely indicate eosinophilia or elevated immunoglobulin E levels.
The patient was treated with topical thiabendazole suspension four times a day. The eruption resolved within two weeks. One year later, the patient reported no complications or recurrence of the eruption.
Previous attempts at destructive therapies, such as cryotherapy, have proved ineffective. Isolated cutaneous cases have been successfully treated with topical thiabendazole suspension, especially when the medication is applied ahead of the advancing edge. However, because of the risk of systemic infection and the ease of oral treatment, some physicians are proponents of routine systemic treatment with oral thiabendazole, albendazole or ivermectin. While thiabendazole has significant side effects that include nausea, vomiting, diarrhea and dizziness, albendazole and ivermectin are reliable and have fewer adverse effects.3 In fact, ivermectin may be given as a single dose with no known toxic side effects.