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PATIENT STORY

A 30-year-old woman presents to a family physician with a rash on most of her forearm that is now encroaching on her hand. She states that it has been going on for 6 months and that 2 months ago she went to an urgent care where she was given two creams to apply to the rash. Fortunately, she had the creams with her, and Figure 144-1 shows the two creams adjacent to the eruption. The physician diagnosed tinea incognito. The urgent care provider recognized the original eruption as fungal but did not know that nystatin only treats Candida and not the dermatophytes that cause tinea corporis. Therefore, the nystatin was useless and the triamcinolone contributed to the rapid growth of this "fungus on steroids." The patient was given 4 weeks of oral terbinafine 250 mg daily, and the tinea incognito cleared completely.

FIGURE 144-1

Tinea corporis on the arm that was incorrectly treated with topical nystatin and topical triamcinolone. As neither agent is effective against T. rubrum, the dermatophyte grew to cover most of the forearm. Nystatin treats Candida and not dermatophytes, so the missed treatment was similar to a misdiagnosis and the steroid allowed this simple tinea infection to become tinea incognito. (Reproduced with permission from Richard P. Usatine, MD.)

INTRODUCTION

Tinea corporis is a common superficial fungal infection of the body, characterized by well-demarcated, annular lesions with central clearing, erythema, and scaling of the periphery.

SYNONYMS

Ringworm, dermatophytosis.

EPIDEMIOLOGY

  • It is estimated that 10% to 20% of the world population is affected by fungal skin infections.1

  • Dermatophytes are the most prevalent agents causing fungal infections of the skin.2

  • Trichophyton rubrum causes the majority of cases of tinea corporis.2

  • The prevalence of tinea corporis gladiatorum (in wrestlers) ranges from 20% to 77%.3

  • Most reported cases of tinea corporis gladiatorum have been caused by T. tonsurans.3

ETIOLOGY AND PATHOPHYSIOLOGY

  • Tinea corporis is caused by fungal species from any one of the following three dermatophyte genera: Trichophyton, Microsporum, and Epidermophyton.

  • Dermatophytes produce enzymes such as keratinase that penetrate keratinized tissue. Their hyphae invade the stratum corneum and spread centrifugally outward.

RISK FACTORS

  • Participation in daycare centers.

  • Wrestling (tinea corporis gladiatorum).3

  • Living in a nursing home.

  • Poor personal hygiene.

  • Living conditions with poor sanitation.

  • Warm, humid environments.

  • Conditions that cause weakening of the immune system (e.g., AIDS, cancer, organ transplantation, diabetes).

DIAGNOSIS

The diagnosis can be made from history, clinical presentation, culture, and direct microscopic observation of hyphae and spores in infected tissue and hairs after KOH preparation. An ultraviolet light (Wood lamp) ...

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