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PATIENT STORY

A 34-year-old woman presents with an itching rash on both feet for the past 6 months (Figure 146-1). She is in otherwise good health and has occasionally tried some over-the-counter (OTC) athlete's foot medicine for this rash with slight improvement. On physical exam, the patient has erythema and scale in the moccasin distribution as well as some of her interdigital spaces. A KOH preparation is positive for branching hyphae with visible nuclei enhanced by the Schwartz Lamkins stain (Figure 146-2). Patient denies a history of hepatitis or heavy alcohol use and would like to try an oral medication because she is tired of the itching. The patient is given oral terbinafine 250 mg daily for 2 weeks.

FIGURE 146-1

Tinea pedis in the moccasin and interdigital distribution. (Reproduced with permission from Richard P. Usatine, MD.)

FIGURE 146-2

Microscopic view of the KOH preparation showing branching hyphae with nuclei that are easy to see under 40× power with Swartz Lamkins stain. (Reproduced with permission from Richard P. Usatine, MD.)

INTRODUCTION

Tinea pedis is a common cutaneous infection of the feet caused by dermatophyte fungus. The clinical manifestation presents in 1 of 3 major patterns: interdigital, moccasin, and inflammatory/vesicular. Concurrent fungal infection of the nails (onychomycosis) occurs frequently.

SYNONYMS

Athlete's foot.

EPIDEMIOLOGY

  • Tinea pedis is the most common human dermatophytosis.1

  • 70% of the population will be infected with tinea pedis at some time.1

  • Prevalence increases with age and it is less common before adolescence.1

ETIOLOGY AND PATHOPHYSIOLOGY

  • A cutaneous fungal infection most commonly caused by Trichophyton rubrum.1

  • Trichophyton mentagrophytes and Epidermophyton floccosum follow in that order.

  • T. rubrum causes most tinea pedis and onychomycosis.

RISK FACTORS

  • Use of public showers, baths or pools—especially if protective footwear is not used.2

  • Household member with tinea pedis infection.2

  • Certain occupations (miners, farmers, soldiers, meat factory workers)—especially where there is use of heavy boots and the feet are warm and sweaty.2

  • Persons experiencing homelessness.3

DIAGNOSIS

TYPICAL DISTRIBUTION AND MORPHOLOGY

Three types of tinea pedis:

FIGURE 146-3

Tinea pedis seen in the interdigital space between the fourth and fifth digits. This is the most common area to see tinea pedis. (Reproduced with permission from Richard P. Usatine, MD.)

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