Athlete’s Foot (Tinea Pedis)

Introduction

Tinea pedis, commonly known as athlete’s foot, is a superficial fungal infection of the skin on the foot. This condition, primarily caused by dermatophyte fungi, is widespread among adults and adolescents and presents frequently in warm, humid climates and in populations engaging in communal activities. The infection most commonly involves the interdigital spaces and plantar surfaces and is known for its recurrent nature due to the persistence of fungal spores in commonly shared environments.

Etiology and Epidemiology

Tinea pedis is caused predominantly by dermatophytes, which are keratinophilic fungi from the genera Trichophyton, Microsporum, and Epidermophyton. The most frequently implicated pathogens are Trichophyton rubrum, T. mentagrophytes/interdigitale complex, and, less commonly, Epidermophyton floccosum. T. rubrum is especially notable for its chronicity and its adaptation to colonizing human skin.

The infection is usually acquired through direct contact with contaminated surfaces, often in moist environments such as locker rooms, pools, and communal showers, where the fungi thrive. Furthermore, occlusive footwear, hyperhidrosis, and certain medical conditions, including diabetes mellitus, increase susceptibility to tinea pedis by providing an ideal environment for fungal growth. The infection is notably rare in children before puberty, potentially due to differences in skin composition and exposure patterns.

Clinical Presentation and Subtypes

Tinea pedis presents with a range of clinical manifestations that can be categorized into several subtypes. Each subtype has distinct morphological characteristics and may require tailored treatment approaches:

  1. Interdigital Tinea Pedis
    The most common form of tinea pedis is interdigital, typically presenting with erythema, scaling, pruritus, and maceration between the toes, particularly in the fourth and fifth interdigital spaces. Patients often report itching and discomfort, and in severe cases, painful fissuring and erosions can occur. Secondary bacterial infection may complicate this presentation, leading to additional symptoms such as exudate or malodor.

  2. Hyperkeratotic (Moccasin-Type) Tinea Pedis
    This form, also referred to as moccasin-type tinea pedis, presents with a chronic, diffuse hyperkeratotic eruption involving the plantar, medial, and lateral aspects of the foot. The affected skin may exhibit erythema and scaling with a characteristic moccasin-like distribution. This variant is commonly associated with chronicity and may extend to include involvement of the toenails (onychomycosis).

  3. Vesiculobullous (Inflammatory) Tinea Pedis
    The vesiculobullous type is marked by pruritic, sometimes painful vesicles or bullae on the soles and sides of the feet, often with underlying erythema. These lesions can rupture, causing significant discomfort, and are frequently localized to the medial aspect of the foot. This presentation tends to have an acute onset and may be exacerbated by secondary bacterial infection if lesions become macerated or crusted.

  4. Ulcerative Tinea Pedis
    In rare and severe cases, ulcerative tinea pedis may develop, particularly in immunocompromised individuals or those with peripheral vascular disease. This type is characterized by extensive ulceration, maceration, and associated bacterial infection, often presenting with pronounced pain and inflammation.

Differential Diagnosis

The differential diagnosis for tinea pedis is extensive and varies by clinical subtype. Interdigital tinea pedis may resemble erythrasma (caused by Corynebacterium minutissimum) or candidal intertrigo, particularly erosio interdigitalis blastomycetica caused by Candida species. In cases of moccasin-type tinea pedis, the differential includes chronic contact dermatitis, palmoplantar psoriasis, juvenile plantar dermatosis, and pitted keratolysis. The vesiculobullous variant may mimic acute dyshidrotic eczema, palmoplantar pustulosis, and scabies.

A potassium hydroxide (KOH) preparation is a standard diagnostic tool that allows for direct visualization of fungal elements. A positive KOH test revealing segmented hyphae confirms a dermatophyte infection, distinguishing tinea pedis from nonfungal conditions. Candida infections, if suspected, will reveal budding yeasts, pseudohyphae, or septate hyphae on the KOH preparation.

Treatment

Treatment of tinea pedis depends on the subtype and severity of the infection. Topical antifungal agents are generally effective and are the first-line treatment for most cases. Common topical antifungals include azoles (e.g., clotrimazole, miconazole), allylamines (e.g., terbinafine, naftifine), and other agents such as butenafine and ciclopirox. These medications inhibit fungal cell membrane synthesis or function, leading to fungal death. Treatment duration varies but is typically around four weeks for interdigital infections, although shorter courses have been effective in some cases.

For hyperkeratotic (moccasin-type) tinea pedis, topical antifungals may be less effective due to the thickness of the affected skin. In these cases, combining antifungal treatment with keratolytic agents (e.g., salicylic acid) can enhance medication penetration. Patients with persistent infections or those unresponsive to topical treatments may require systemic antifungal therapy, such as oral terbinafine, itraconazole, or fluconazole. These agents are generally administered for two to six weeks, depending on the specific medication and infection severity.

Systematic reviews of randomized trials have demonstrated the efficacy of allylamines over azoles in achieving higher cure rates in tinea pedis, although the choice of agent may also depend on individual tolerance, cost, and availability.

Adjunctive Therapy and Prevention

In cases of severe maceration or vesiculation, Burow solution (1% aluminum acetate) may be used as a soak to reduce moisture and maceration. Placing absorbent materials like gauze between the toes can also help limit friction and moisture accumulation, reducing fungal growth.

Preventive measures are crucial for patients prone to recurrent infections. Key strategies include:

  • Moisture control: Keeping the feet dry, especially the interdigital spaces, is essential. Patients should dry their feet thoroughly after bathing and avoid wearing occlusive footwear.

  • Footwear and socks: Wearing breathable footwear and socks made of moisture-wicking materials, and changing socks regularly, can help reduce moisture build-up.

  • Antifungal powders and sprays: These can be applied to shoes and socks to reduce the presence of fungal spores.

  • Avoiding communal barefoot walking: Limiting exposure to shared surfaces like locker rooms or public showers can reduce the risk of infection.

Conclusion

Tinea pedis is a prevalent and often recurrent infection that can significantly impact quality of life if left untreated. Recognizing the clinical subtypes and implementing effective treatment strategies, including both pharmacologic and preventive measures, can help manage and prevent tinea pedis. For persistent or complicated cases, consultation with a dermatologist is recommended to ensure an accurate diagnosis and appropriate therapy, including potential systemic treatments.