dermatophyte infections

Why has this itchy rash resisted corticosteroids?

DAVID L. KAPLAN, MD—Series Editor
University of Missouri Kansas City, University of Kansas

David L. Kaplan, MD––Series Editor: Dr Kaplan is clinical assistant professor of dermatology at the University of Missouri Kansas City School of Medicine and at the University of Kansas School of Medicine. He practices adult and pediatric dermatology in Overland Park, Kan.

A Photo Quiz To Hone Dermatologic Skills 

Dermatophyte infection

A 68-year-old woman has had itchy spots on the anterior neck and left arm for 2 months. Over-the-counter antipruritic creams have been ineffective. She denies using any new preparations that may have caused the rash, such as perfumes, moisturizers, or other cosmetics.

A potassium hydroxide (KOH) evaluation performed a month ago was negative; a potent corticosteroid cream was prescribed, but the rash has failed to clear.

What is the most appropriate next step?

A. Prescribe a short-term tapering course of prednisone.

B. Perform a skin biopsy.

C. Perform a second KOH evaluation.

D. Perform patch testing for possible contactants.

E. Recommend that she use hypoallergenic skin products.

(Answer on next page.)

    ANSWER—Dermatophyte infection     

Dermatophyte infection

A false-negative KOH result can occur, particularly if fungus-containing stratum corneum has been washed or scratched off the skin before the specimen is obtained. For this reason, a second KOH evaluation, C, was done—this time with positive results. During further questioning, the patient revealed she had a lap dog; the pet was suspected of carrying the dermatophyte.

The patient was given antifungal therapy. She was told to take her dog to a veterinarian for treatment.