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[8 min read] Common fungal infections of the skin

Fungal infections of the skin can be quite common even in otherwise healthy individuals. The most commonly encountered skin infections caused by fungi are due to dermatophytes. These infections are generally diagnosed by history and confirmed by microscopic evaluation of skin scrapings or by biopsy. Dermatophyte infections can involve any surface of the body including scalp, feet, groin, and nails.

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Dermatophyte infections of the scalp are known as tinea capitis. Worldwide, the most common organism to cause this infection is Microsporum canis. Other common offenders include Trichophyton tonsurans and Trichopyton violaceum. Tinea capitis presents with scaly, round plaques of hair loss with pustules. It is very itchy, and is most common in children. Severe cases result in kerion, where patients get a mass-like abscess and swollen lymph nodes. These infections may result in permanent scarring hair loss. It’s best to treat tinea capitis with systemic antifungal therapy.

Infections of the body are known as tinea corporis.  Tinea corporis presents with itchy, red scaly plaques and may be mistaken for eczema or psoriasis. The most common dermatophyte to cause this infection is Trichophyton rubrum. Treatment of tinea corporis may involve topical or systemic antifungals, depending on severity of the disease or previously failed therapies.

Tinea pedis is a dermatophyte infection of the feet, commonly known as “athlete’s foot”. Patients may have scaly, itchy plaques in a moccasin distribution covering the sole and the peripheral edges of the feet. Tinea pedis often looks like eczema or palmoplantar psoriasis, but involvement of the nails or web spaces between the toes provides additional clues for this diagnosis. The most common organisms causing tinea pedis are Trichophyton rubrum and Epidermophyton floccosum. There is also a blistering variant which is caused by Tricophyton mentagrophytes. Treatment of athlete’s feet involves use of topicals, and in some cases, systemic therapies. Keeping the feet dry with antifungal powders, absorbent powders, and good overall hygiene practices are all helpful ways to prevent recurrences.

Two feet one had syndrome is a phenomenon where a tinea infection affects both the feet and one hand as the name-sake suggests. Trichophyton rubrum and Trichophyton mentagrophytes are usually the culprit behind these infections. It’s thought that this condition affects the dominant hand with which the patient is using to scratch their feet, resulting in spread of the fungal infection.

Tinea cruris is a dermatophyte infection affecting the groin. Commonly known as “jock-itch”, patients who have this infection report itchy, red rash in the groin and thighs. Some patients will have concurrent infection of their feet as well. There is thought that patients may sometimes spread the infection from their toenails or feet to their groin when they are putting on their undergarments. Putting on socks prior to getting dressed can be helpful in patients with recurring infections. Treatment of tinea cruris usually starts with topical therapies, but may require systemic therapy when topical creams fail. Other disorders that may mimic tinea cruris include eczema and inverse psoriasis.

When tinea infections go deeper, it becomes a Majocchi’s granuloma. This type of infection is deeper and involves the hair follicles. Majocchi’s granulomas often arises after patients use topical steroids to treat the itch of a pre-existing fungal infection. Patients will have erythematous, inflamed and itchy plaques or nodules on the skin. Systemic antifungals are always recommended to treat this deeper infection.

The diagnosis of fungal infections is often made based on clinical history and physical examination. Occasionally, a skin scraping evaluated with KOH under microscopy may be helpful to demonstrate the hyphae and confirm diagnosis. Biopsy may also be helpful to identify fungal elements if the diagnosis is unclear.

Treatment of common tinea infections involves topical and systemic therapies. The most effective agents include topical or systemic terbinafine, systemic griseofulvin, or topical ketoconazole. Powder formulations of antifungals can be helpful to reduce moisture, which often propagates fungal infections. It is important never to use systemic ketoconazole as there is a significant risk of dangerous liver toxicity. When considering systemic antifungals, it is important to check for drug interactions as many of these medications may interact with common medications.

– Dr Lulu Wong

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References

  • Christine T Lauren. Review of Dermatology, Chapter 5.4 Fungal diseases. Elsevier. 2017. P305-306.
  • Zhan P, Ge YP, Lu XL, She XD, Li ZH, Liu WD. A case-control analysis and laboratory study of the two feet-one hand syndrome in two dermatology hospitals in China. Clin Exp Dermatol. 2010 Jul;35(5):468-72. doi: 10.1111/j.1365-2230.2009.03458.x. Epub 2009 Oct 23. PMID: 19874338.

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