An adolescent presents with a ring-shaped skin lesion with central clearing. The diagnosis is confirmed by the presence of which finding on skin scrapings?

• A. Positive patch test
• B. Hyphae on a KOH prep
• C. Gram-positive cocci on Gram stain
• D. Multinucleated cells on Tzanck smear

Answer: (B)

A ring-shaped skin lesion with central clearing points to a dermatophyte infection of the skin (tinea corporis). To confirm this on skin scrapings, a potassium hydroxide preparation is used. KOH dissolves the keratin so fungal elements are visible under the microscope; in tinea you’ll see branching, septate hyphae invading the stratum corneum. This finding specifically supports a fungal etiology.

Other tests point to different conditions. A patch test would indicate allergic contact dermatitis, not a fungal infection. Seeing Gram-positive cocci on Gram stain would suggest a bacterial infection such as impetigo or folliculitis. Multinucleated cells on a Tzanck smear are associated with herpesviruses (HSV or VZV), not dermatophytes.