Aileen Chang, MD, FAAD, discussed infestations that can make any dermatologist’s skin crawl at the Society of Dermatology Physician Assistants 19th Annual Fall Dermatology Conference in Los Angeles, CA. Dr Chang is an assistant professor of clinical dermatology at University of California, San Francisco.

Ectoparasitosis are dermatologic diseases caused by parasites that live on the outside of their hosts, including mites, ticks, fleas, lice, bed bugs, flies, and hookworms. These arthropods and nematodes cause hypersensitivity reactions in the skin and can be annoying and uncomfortable for patients, and the scratching in response to the intense itch caused by the parasites can lead to bacterial infection.

The morphology of ectoparasitoses often are urticarial plaque with a central papulovesicle, but they can also show bullae and purpura, and patients can present with excoriated papules because of itching. Dr Chang shared the case of a patient who was ultimately diagnosed with bedbug bites, highlighting that the patient’s live-in partner did not have a skin reaction to the infestation. Dr Chang noted that it is important in all cases of excoriated papules to really identify the cause of the bite. Identifying the cause of bites should focus on the distribution of the lesions on the body, a relevant history from the patient, and recommendation of professional pest control services to help narrow down the cause. Potential causes of bites and their distribution and history patterns include:

• Bedbugs: clustered in one location but can also be widespread on the body; often occur after travel or change in living situation
• Scabies: found in webspaces, wrists, ankles, umbilicus, male genitalia, and female areola; occur when a patient has had close contact with someone with an infestation and in overcrowding situations
• Body lice: occur along clothing seams; history includes lack of access to hygiene services and an inability to care for self
• Avian, rat, or mouse mites: lesions are typically widespread; occur in patients who have bird or rat nests near the home, people who raise chickens or have pets, and sometimes in people who live in areas undergoing construction or renovations
• Flea bites: seen most typically around the ankles and lower legs but can be higher on the body in children; associated with pet dogs or cats, especially if the animal has not been recently inspected

Dr Chang then provided several different pearls for identifying various ectoparasitoses, such as looking for a “wake sign,” which shows the burrowing pattern of scabies, and performing a “clothing biopsy” for identifying body lice.

Reference
Chang A. What bit me? Diagnostic & management pearls for ectoparasitic infestations. Presented at: Society of Dermatology Physician Assistants 19th Annual Fall Dermatology Conference; November 4-7, 2021; Los Angeles, CA.