Common Foot Infections

Case 2. PJ is a 48-year-old patient who comes to your office with a painful lesion on the bottom of his left foot. He reports gaining 11 kg (25 lb) since retiring from the military last year. Last month, he joined a gym and started swimming for exercise. You note a hyperkeratotic lesion approximately 1.5 cm in diameter on the plantar surface of the foot. There is also flaking of the skin between the first and second toes with maceration and underlying erythema.

Tinea pedis (ie, athlete’s foot) is a common cutaneous fungal infection seen in industrialized countries.^1–3 Dermatophytes are the most prevalent pathogenic fungi causing an inflammatory response in the epidermis of the foot. Trichophyton species (ie, Trichophyton rubrum and Trichophyton interdigitale) are dermatophytes with an affinity for keratinized tissues, such as skin, hair, and nails.^1,2

There are three major risk factors for tinea pedis: direct contact, predisposing conditions, and environmental conditions. Direct contact with a pathogenic fungus may be in the form of fungal spores or infected skin fragments.¹ Transmission is common between family members, but contamination can occur from infected belongings, pets, or soil.⁴ Predisposing medical conditions that result in poor circulation or immune suppression increase the likelihood of superficial skin infection or prolonged healing.¹ Fungi thrive in warm, moist environmental conditions; wearing occlusive footwear provides ideal conditions for fungal proliferation.³

Tinea pedis infections can have diverse clinical presentations, especially on different skin tones. Interdigital, hyperkeratotic, and vesiculobullous are the three main forms.⁵ The most common location of tinea pedis, especially in children, is in the interdigital spaces. The main symptom is itching.^6,7 Interdigital infections present with erythema, white scaling, peeling, and maceration.¹ Adjacent areas of the foot also are commonly infected. A complicated form of interdigital tinea pedis, dermatophytosis complex, can result from secondary bacterial infections. Gram-positive bacteria (ie, Staphylococcus aureus or streptococci) and gram-negative bacteria (ie, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella or Proteus species) may cause infection in dermatophytosis complex. Secondary infection with these bacteria can cause a foul odor, erosions, and maceration of the skin.

The second most common form of tinea pedis is hyperkeratotic, or moccasin-type.^1,8 This type of tinea pedis is characterized by varying forms of chronic hyperkeratotic scaling patches and erythema of the skin in the area of the foot that would be covered by moccasin style footwear.^8,9 Lesions typically are located on the dorsum of the foot, sparing the distal portion.^7,10 The edge of the lesion may be arcuate, annular, and slightly elevated.¹¹ The hyperkeratotic form of tinea pedis is mostly asymptomatic and likely to be resistant to treatment.^12,13