A 37-year-old man noted the recent appearance of a very itchy and scaly rash extending from the underarm onto the upper arm. He was in good health, had no pets, and had no exotic travel history.
Key point: The annular nature of this eruption suggests a number of potential diagnoses. However, the intense pruritus most strongly suggests tinea or granuloma annulare. Most of the other causes of annular skin lesions are asymptomatic. A KOH preparation disclosed innumerable fungal hyphae, establishing the diagnosis of tinea corporis.
Treatment: Because of the circumscribed nature of the tinea, the patient was instructed to apply naftifine 2% cream to the affected area once daily. The lesions cleared in 2 weeks.
Note: While he did not own a pet himself, he often visited a friend who owned a new puppy. It is presumed that this was the environment from which the dermatophyte originated.