Several weeks ago, this 14-year-old boy developed an itchy spot on his neck. Concerned that the problem was “ringworm,” the boy’s grandfather took him to the primary care provider, who prescribed nystatin cream. This produced modest improvement in the appearance of the lesion but had no effect on the associated itching. At that point, they were referred to dermatology for further evaluation.
The patient denies any other skin problems. The only animal he has been exposed to is his own dog, who has been part of the household for years. The boy is not involved in contact sports (eg, football, wrestling), and he reports that none of his siblings or friends have any skin complaints.
He is otherwise healthy and does not take any prescription medications.
The “rash” consists of a single, 2-cm lesion on the patient’s anterolateral neck. It is perfectly round and slightly erythematous, with a cleared center and scaly advancing margin. Palpable adenopathy is evident just above the lesion. There are no other lesions elsewhere, and the patient’s skin is otherwise unremarkable.
What is the diagnosis?