A 19-year-old man develops a rash in the groin area. On examination, it is a large well-demarcated area of tan-brown discoloration around his left inguinal area. There is some scaling of the lesion when brushed with a tongue depressor. Which of the following is the most appropriate initial diagnostic test?
punch biopsy of skin Tzanck smear potassium hydroxide (KOH) preparation of scrapings blood culture for fungi