In which condition would you expect to find the presence of hyphae on a KOH prep?

The presence of hyphae on a KOH prep is significant for diagnosing fungal infections. A KOH (potassium hydroxide) preparation is a laboratory test where skin scrapings or samples are treated with potassium hydroxide to clear away keratin and other debris, making fungal elements more visible under a microscope. When hyphae are detected, it indicates the presence of dermatophytes or yeast, both of which are associated with fungal infections such as tinea (ringworm), candidiasis, and others.

In contrast, conditions like psoriasis, erythema marginatum, and actinic keratosis do not involve fungal pathogens and would not present with hyphae on a KOH prep. Psoriasis is an autoimmune condition characterized by rapid skin cell turnover leading to thickened plaques, and KOH prep would show no fungal elements. Erythema marginatum is a skin manifestation associated with rheumatic fever and does not involve fungi. Actinic keratosis is a precancerous skin condition resulting from sun damage, also unrelated to fungal infections.

Thus, in the context of skin conditions where hyphae are identified on a KOH prep, a fungal infection is the correct choice.