A 16-year-old girl presented with an extremely pruritic rash on the ventral aspect of both arms. She was in good health, had never suffered from eczema, and took no medications.
Key point: The symmetry and limited distribution of the eruption suggests that it may be caused by something that comes in contact with the inside of the arms. Lesional morphology and distribution is characteristic of ectoparasite bites, which occur when a human carries a pet—usually a kitten or puppy—as if the animal were a human newborn baby. On direct questioning, the patient noted the acquisition of a new kitten in the last few weeks. The most common ectoparasite responsible for this type of eruption is the mite, cheyletiella.
Treatment: The animal should be examined to confirm infestation and then professionally treated by a veterinarian to preclude ongoing problems. Old bites spontaneously resolve.
Note: Always inquire about exposure to animals when you encounter an unusual rash.