Several months ago, this 8-year-old boy began losing hair from his scalp. Other than mild itching, there are no associated symptoms. The patient has no pets at home, but he spends his after-school hours with his cousin, who does.
The child is allergy prone but otherwise healthy. No one else in the family (ie, his two younger siblings) has been similarly affected.
EXAMINATION
About three-quarters of the hair is missing from a 6-cm oval patch on the parietal scalp. A few short hairs remain. The skin in this area is slightly edematous, with focal areas of broken, scaly skin.
Palpation of the head and neck reveals adenopathy in the nuchal area of the affected side. A KOH prep is performed with a #10 blade; the sample includes hairs as well as skin.
What is the diagnosis?