Derm Dx: Itchy blister between the toes - Clinical Advisor

Derm Dx: Itchy blister between the toes

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  • Bullous Tinea 1_0713 Derm Dx

  • Bullous Tinea 2_0713 Derm Dx

A 55-year-old patient presents complaining of an itchy blister between her toes that she said, “popped up overnight.” She has well controlled type 2 diabetes and is otherwise healthy.

Tinea pedis, also known as "athlete's foot," is the most common fungal disease in humans. The most prevalent variant is caused mainly by the dermatophyte Trichophyton rubrum. This variant involves erythema and scaling that may affect both the bottom and...

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Tinea pedis, also known as “athlete’s foot,” is the most common fungal disease in humans. The most prevalent variant is caused mainly by the dermatophyte Trichophyton rubrum. This variant involves erythema and scaling that may affect both the bottom and sides of the feet in a so-called “moccasin” or “sandal” distribution. Sometimes one hand is similarly affected; when both feet are affected concomitantly, this is called “one-hand, two-feet” tinea. 

This patient has bullous tinea pedis, a more inflammatory variant of tinea pedis often caused by Trichophyton mentagrophytes. Bullous tinea pedis most commonly appears as vesicles and bullae along the arch and sides of the feet. These blisters contain a straw-colored fluid and generally itch or burn significantly. 

T. mentagrophytes is also responsible for some cases of interdigital tinea pedis, in which erythema, maceration, scaling and fissuring occur between the toes. The areas of blistering and maceration may become secondarily infected with both gram-positive and gram-negative bacteria. 

Rarely, inflammatory cases of tinea pedis may be associated with dermatophytid of the hands. This presents as pruritic, small, clear vesicles distributed on the fingers and palms that arise in association with inflammatory tinea pedis.  The lesions on the hands do not actually contain fungal organism, but they resolve when the tinea pedis is adequately treated. The pathoetiology of the dermatophytid response is poorly understood, but it is likely an immune-mediated phenomenon. 

In order to confirm a diagnosis of bullous tinea pedis, clinicians must unroof the bullae, scrape the underside of the roof onto a glass slide and inoculate the specimen with potassium hydroxide. A glass coverslip should then be placed on top, and the slide should be gently heated. If present, fungal hyphae may then be visualized using a microscope. 

In this patient, the roof of the blister was removed and sent for histologic evaluation. Hyphae were present in the specimen, thus confirming the suspected diagnosis of bullous tinea pedis. 

Tinea pedis is common in patients who sweat profusely or who wear occlusive footwear.  Therefore, keeping the feet dry is essential to prevent tinea pedis. Additionally, miconazole and tolnaftate antifungal powders may be used. 

In mild cases, topical antifungals may be used. The most effective topical antifungals are the allylamines butenafine and terbinafine. In more severe cases, oral antifungals such terbinafine, itraconazole and fluconazole are required.            

Adam Rees, MD, is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine in Houston.

References

  1. Bolognia J, Jorizzo JL, Rapini RP. “Chapter 76: Fungal Diseases.” Dermatology. St. Louis: Mosby/Elsevier, 2008.
  2. James WD, Berger TD, Elston DM et al. “Chapter 15: Diseases Resulting from Fungi and Yeasts.” Andrews’ Diseases of the Skin: Clinical Dermatology. Philadelphia: Saunders Elsevier, 2006.
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