eMedicine Specialties > Dermatology > Fungal Infections

Tinea Pedis: Differential Diagnoses & Workup

Author: Courtney M Robbins, MD, Resident Physician, Department of Dermatology, University of Alabama at Birmingham School of Medicine
Coauthor(s): Boni E Elewski, MD, Professor, Department of Dermatology, University of Alabama at Birmingham
Contributor Information and Disclosures

Updated: Nov 13, 2008

Differential Diagnoses

Candidiasis, Cutaneous
Pityriasis Rubra Pilaris
Contact Dermatitis, Allergic
Psoriasis, Plaque
Dyshidrotic Eczema
Psoriasis, Pustular
Erythema Multiforme
Syphilis
Erythrasma
Friction Blisters

Other Problems to Be Considered

Autoimmune blistering disorders
Bacterial infection
Eczematous dermatitis
Xerosis

Workup

Laboratory Studies

  • Order direct potassium hydroxide (KOH) staining for fungal elements. Usually, the fungal elements are easily identified from scaly lesions. Using counterstains may enhance the visibility of the hyaline hyphae found in dermatophyte infections. Examples include the chitin-specific stains chlorazol black E, which stains hyphae blue-black, and calcofluor, which fluoresces hyphae under a fluorescent microscope.
    • A sample from skin scrapings may be obtained using a No. 15 blade.
    • When blisters are present, the highest fungal yield is obtained by scraping the roof of the vesicle.
  • A fungal culture may be performed to confirm the diagnosis and to identify the pathogenic species.
    • Common media include dermatophyte test medium, Mycosel, or mycobiotic agar.
    • Use caution when choosing the correct culture medium because certain media (eg, dermatophyte test medium) contain cycloheximide, which inhibits the growth of nondermatophyte molds. Because these fungi can be a factor in tinea pedis, use agar without cycloheximide.

Histologic Findings

A skin biopsy and histopathological study are rarely needed to confirm a diagnosis of tinea pedis. Fungal elements within the stratum corneum can usually be identified using periodic acid-Schiff or Gomori methenamine-silver stain but may be sparse or absent in inflammatory or interdigital tinea pedis complicated by secondary bacterial infection. Neutrophils may be noted within the stratum corneum, a finding that should prompt consideration of a dermatophyte infection. In vesicular tinea pedis, spongiotic intraepidermal vesicles are present; in the chronic hyperkeratotic (moccasin) type, hyperkeratosis and epidermal acanthosis usually are present. Both types are associated with an acute or chronic dermatitis that may contain eosinophils.

More on Tinea Pedis

Overview: Tinea Pedis
Differential Diagnoses & Workup: Tinea Pedis
Treatment & Medication: Tinea Pedis
Follow-up: Tinea Pedis
References
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References

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Further Reading

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Keywords

athlete's foot, ringworm of the feet, dermatophytosis, dermatophytid, Trichophyton rubrum, T rubrum, Trichophyton mentagrophytes, T mentagrophytes, Epidermophyton floccosum, E floccosum, Scytalidium hyalinum, S hyalinum, Scytalidium dimidiatum, S dimidiatum

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Contributor Information and Disclosures

Author

Courtney M Robbins, MD, Resident Physician, Department of Dermatology, University of Alabama at Birmingham School of Medicine
Courtney M Robbins, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Medical Association, and Women's Dermatologic Society
Disclosure: Nothing to disclose.

Coauthor(s)

Boni E Elewski, MD, Professor, Department of Dermatology, University of Alabama at Birmingham
Boni E Elewski, MD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Abbott #1 Grant/research funds Investigator; Amgen Honoraria Consulting; Amgen #1 Grant/research funds Investigator; Amgen #2 Stock Stockholder; Barrier #1 Grant/research funds Investigator; Centocor #1 Grant/research funds Investigator; Intendis  Consulting; Mediquest #1 Grant/research funds Investigator; NanoBio Honoraria Consulting; Novartis #1 Grant/research funds Investigator

Medical Editor

Gregory J Raugi, MD, PhD, Professor, Department of Internal Medicine, Division of Dermatology, University of Washington at Seattle; Chief, Dermatology Section, Primary and Specialty Care Service, Veterans Administration Medical Center of Seattle
Gregory J Raugi, MD, PhD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Nothing to disclose.

Pharmacy Editor

Michael J Wells, MD, Associate Professor, Department of Dermatology, Texas Tech University Health Sciences Center
Michael J Wells, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Medical Association, and Texas Medical Association
Disclosure: Nothing to disclose.

Managing Editor

Lester F Libow, MD, Dermatopathologist, South Texas Dermatopathology Laboratory
Lester F Libow, MD is a member of the following medical societies: American Academy of Dermatology, American Society of Dermatopathology, and Texas Medical Association
Disclosure: Nothing to disclose.

CME Editor

Catherine Quirk, MD, Clinical Assistant Professor, Department of Dermatology, Brown University
Catherine Quirk, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology
Disclosure: Nothing to disclose.

Chief Editor

William D James, MD, Paul R Gross Professor of Dermatology, University of Pennsylvania School of Medicine; Vice-Chair, Program Director, Department of Dermatology, University of Pennsylvania Health System
William D James, MD is a member of the following medical societies: American Academy of Dermatology and Society for Investigative Dermatology
Disclosure: elsevier Royalty Other; american college of physicians Honoraria Other

 
 
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