Negative-Culture Tinea Corporis

A 49-year-old man was concerned about a right flexor forearm lesion that had been increasing in size for 6 weeks. The light pink, well-demarcated, 5-cm, circular lesion featured slight peripheral elevation with ulceration, crusting, and a relatively clear central area. A culture of material from the lesion was negative for fungi. A potassium hydroxide evaluation was not performed.

The eruption cleared completely after a 4-week course of econazole cream applied twice daily. The negative fungal culture result may have occurred because the specimen was taken from an area of the lesion that contained relatively little crusting.

Since the infection spreads centrifugally, specimens for fungal testing must be taken from the periphery or advancing edge of the lesion, where dermatophytes are present.