Chapter 6: Infections and Infestations
Fungal Infections: Tinea Corporis
Tinea Corporis is a fungal infection localized to the uppermost layers of the skin. It is commonly known as “ringworm”. The fungi that cause tinea corporis are called dermatophytes.
What does it look like?
The characteristic lesions are circular with a raised red border and associated scale. Most patients with tinea corporis are itchy, although the itch is typically less severe than that associated with nummular eczema.
Hover over image for caption.
What causes it?
There are several species of fungus associated with tinea corporis. Some of these are anthropophilic (meaning that they prefer to infect humans) and some are zoophilic (meaning that they prefer to infect animals). People get the infection when they come in contact with another person or an animal with the fungus on their skin.
How is it diagnosed?
In some cases, the presentation is very clear and it can be diagnosed clinically. In most cases though, it is difficult to tell apart from nummular eczema, which is also round, scaly, red, and itchy. For this reason, it is best to diagnose with a KOH prep, which is relatively quick and easy to do in clinic if there is an available microscope, or the scrapings can be sent to the laboratory for confirmation.
To perform a KOH prep, scrape the edge of one glass slide over the scaly edge of the lesion so that scale comes off onto a second glass slide. Cover with 1 drop of KOH and cover slip. The long branching hyphae are visible crossing the skin cells in the clump of skin seen on the slide. The hyphae become more clearly visible with time, so it is often helpful to set the slide aside and review at the end of clinic (see Appendix for further details).
How is it treated?
Unless it covers a large amount of the body, tinea corporis can be treated with antifungal creams. The most commonly used are terbinafine or the “–azoles” such as clotrimazole and ketoconazole. These can be used twice a day for 2-4 weeks. Topical steroids should not be used in treating tinea corporis because, while they may decrease the redness and scaling, they also diminish the patient’s immune reaction to the fungus and allow the organism to multiply and may result in more resistant disease.
Oral therapy – indicated for tinea capitis, onychomycosis and extensive tinea corporis
Specific terminology for other forms of fungal infection caused by dermatophytes:
Tinea faciei: Fungal infection of the face.
Tinea barbae: Fungal infection of the beard.
Tinea capitis: Fungal infection of the scalp – can develop into a large boggy lesion called a kerion.
Tinea cruris: Fungal infection of the groin.
Tinea pedis: Fungal infection of the feet.
Tinea manuum: Fungal infection of the hand (sometimes called “2-foot 1-hand” because it usually involves both feet but only one hand).
Tinea nigra: A fungal infection caused by one particular fungus, which makes the skin turn brown (Hortaea werneckii).
Tinea incognito: Fungal infection that has been treated with steroids. Since the inflammatory reaction is lessened, the infection looks better, but actually is getting worse. It can develop fungal folliculitis (Majocchi’s granulomatosis) if the fungus tracks into the hair follicles, which requires treatment with oral antifungals.
Onychomycosis: Fungal infection in the nail – does not clear without oral antifungals. Also sometimes referred to as tinea unguium.
