Why has this itchy rash resisted corticosteroids?

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     

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.