A 44-year-old man presents with what his primary care provider called “ringworm.” The condition has not responded to topical and oral antifungal medications (clotrimazole and oral terbinafine). Fortunately, the lesions are not particularly symptomatic.
The patient, who works in an oil field, claims to be in otherwise good health. He has no pets at home, and no one else in his household has been similarly affected. He is taking no medications at this time.
EXAMINATION
Multiple arcuate and annular scaly lesions are seen, most densely distributed across the patient’s upper back and posterior shoulders. They thin out inferiorly and are missing entirely below the waist.
Many of the lesions are larger than 10 cm (though on average half that size). They have well-defined, scaly margins and mostly clear centers. There is minimal erythema.
A KOH prep of the lesions does not show fungal elements. A 4-mm punch biopsy is performed, the results of which will be discussed in the next section.
What is the diagnosis?