Treatment-Resistant Tinea Corporis

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For 4 years, a 10-year-old boy had a recurrent rash on his left leg. He had been treated for presumed ringworm with multiple topical antifungal medications, including terbinafine, ciclopirox, and ketoconazole, each used twice daily for several weeks with near complete clearing after each course. However, the rash recurred in the same location several weeks to months after therapy was discontinued.

Examination revealed coalescing annular plaques with scaling, central clearing, and a rim of hyperpigmentation on the anterior left leg. A potassium hydroxide (KOH) preparation of skin scrapings revealed florid hyphae on microscopy, and culture of the lesion grew Trichophyton rubrum. Although unusual in morphology, the rash was consistent with persistent tinea corporis.

Tinea corporis can be managed with topical antifungal agents alone, applied on and 2 cm around the lesion, once or twice daily. Therapy should be continued for at least a week after resolution of the rash.¹ In severe cases, or when the rash fails to respond to multiple topical agents, oral agents may be required.² Although most cases of tinea resolve with these therapies, dermatophyte infections can recur, most commonly on the soles, toe webs, or nails.³ This is thought to be secondary to selective anergy to the dermatophyte antigen. Alternatively, it may be because of mannan (a glycoprotein that is spontaneously shed from T rubrum), which may suppress the cell-mediated immunity that would normally clear such infections.^4,5 In cases of refractory tinea corporis presenting with an uncharacteristic, potentially confusing morphology, culture and sensitivity testing in addition to KOH preparation can provide important diagnostic and therapeutic information.

This patient was treated with oral terbinafine sprinkles, 250 mg daily for 6 weeks, and topical ketoconazole cream. He was also instructed to use antifungal powder in his shoes and rollerblades. ■