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Dermatology for the Practicing Allergist: Tinea Pedis and Its Complications

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Dermatology for the Practicing Allergist: Tinea Pedis and Its Complications

Muhannad Al Hasan et al. Clin Mol Allergy.

Abstract

Tinea pedis is a chronic fungal infection of the feet, very often observed in patients who are immuno-suppressed or have diabetes mellitus. The practicing allergist may be called upon to treat this disease for various reasons. Sometimes tinea infection may be mistaken for atopic dermatitis or allergic eczema. In other patients, tinea pedis may complicate allergy and asthma and may contribute to refractory atopic disease. Patients with recurrent cellulitis may be referred to the allergist/immunologist for an immune evaluation and discovered to have tinea pedis as a predisposing factor. From a molecular standpoint, superficial fungal infections may induce a type2 T helper cell response (Th2) that can aggravate atopy. Th2 cytokines may induce eosinophil recruitment and immunoglobulin E (IgE) class switching by B cells, thereby leading to exacerbation of atopic conditions. Three groups of fungal pathogens, referred to as dermatophytes, have been shown to cause tinea pedis: Trychophyton sp, Epidermophyton sp, and Microsporum sp. The disease manifests as a pruritic, erythematous, scaly eruption on the foot and depending on its location, three variants have been described: interdigital type, moccasin type, and vesiculobullous type. Tinea pedis may be associated with recurrent cellulitis, as the fungal pathogens provide a portal for bacterial invasion of subcutaneous tissues. In some cases of refractory asthma, treatment of the associated tinea pedis infection may induce remission in airway disease. Very often, protracted topical and/or oral antifungal agents are required to treat this often frustrating and morbid disease. An evaluation for underlying immuno-suppression or diabetes may be indicated in patients with refractory disease.

Figures

Figure 1
Figure 1
Interdigital tinea pedis affecting the space between the third and fourth digits. Tinea infections between the toes are common due to high moisture content and occlusion and often present with itching, burning, and/or malodor. This figure shows a man with dry-type tinea pedis in the third interspace. (Photograph kindly provided by Dr. Stuart Leicht, Division of Dermatology, East Tennessee State University).
Figure 2
Figure 2
Bilateral moccasin type tinea pedis lesions. Moccasin type tinea pedis is a more prolonged form of tinea infection that surrounds the sole and lateral aspects of the foot in a slipper or moccasin distribution. 2A shows hyperkeratotic skin on the medial and bottom portions of the foot. 2B shows moccasin type tinea pedis on the lateral portion of the foot.
Figure 3
Figure 3
Vesiculobullous type tinea pedis on the plantar surface of the feet. This type of tinea pedis usually causes pustules or vesicles on the instep and plantar surfaces of the feet. Bacterial infection should be ruled out by microscopy or culture. (Photograph kindly provided by Dr. Stuart Leicht, Division of Dermatology, East Tennessee State University.)
Figure 4
Figure 4
Activation of cutaneous and/or circulating T cells by fungal antigens could induce a Th2-dominant response leading to elaboration of IL-4, IL-13 and IL-5. The first 2 cytokines can lead to two pivotal effects: Synthesis of IgE by B cells and endothelial activation leading to eosinophil recruitment by a vascular cell adhesion molecule (VCAM)-very late activating antigen 4 (VLA-4) adhesion molecule pathway. Both IgE and eosinophils play a prominent role in atopic disease. IgE in the presence of antigen can cross-link mast cells leading to further cytokine, chemokine and mediator production. The other cytokine, IL-5, enhances eosinophil production from the bone marrow, eosinophil activation, survival, recruitment and degranulation. These processes can result in expression of atopic disease, from rhinitis and asthma to atopic dermatitis.
Figure 5
Figure 5
KOH preparation of fungal hyphae. This slide shows the branched hyphae of T. rubrum. Scrapings from the outer edge of a tinea lesion should be taken with a sterile scalpel, placed on a slide and KOH applied. KOH dissolves the epithelial cells seen in the background and leaves the fungus to be viewed by microscopy.

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