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. (See Figure below) 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
A KOH preparation is useful when performed on scaling skin lesions, when a fungal etiology is suspected. The scraped scales are placed on a microscope slide, treated with one or two drops of KOH solution, and examined for hyphae, pseudo hyphae, or budding yeast. A Tzanck smear is a cytologic technique for the diagnosis of herpes virus infection from vesicles, and diascopy is to assess whether a skin lesion will blanch with pressure.
Skin