What Is It, Causes, Signs and Symptoms, Diagnosis, Treatment, and More
Author: Anna Hernández, MD
Illustrator: Jillian Dunbar
What is a dermatophyte infection?
Tinea infections are one of the most common causes of superficial fungal infections around the world, and are distinguished by the area of the body affected. For instance, tinea corporis (i.e. ringworm) affects the arms, trunk, and legs; tinea capitis (i.e. scalp ringworm) affects the scalp and hair shafts; tinea faciei affects facial skin; tinea cruris (i.e. jock itch) affects the groin and inner thighs; tinea pedis (i.e. athlete’s foot) and tinea manuum affect the feet and hands, respectively; and tinea barbae affects facial hair follicles of bearded individuals. Dermatophyte nail infections are commonly known as dermatophyte onychomycosis or tinea unguium.Individuals with decreased immune response, older individuals, and children are at an increased risk of developing a dermatophyte infection. Other general risk factors include diabetes mellitus, poor circulation, and topical corticosteroid use.
What causes a dermatophyte infection?
Dermatophyte infections are caused by dermatophytes; a group of filamentous fungi that require keratin for growth. Keratin is a family of structural proteins that are found in the hair, nails, and outermost layers of the skin. There are over 20 species of dermatophytes which are classified into three genera: Trichophyton, Microsporum, and Epidermophyton.Dermatophytes can be further classified into different subtypes—anthropophilic, zoophilic, and geophilic— according to their natural habitat. Anthropophilic dermatophytes, such as Trichophyton rubrum and Trichophyton tonsurans, are the main cause of human dermatophytosis. They are often transmitted from one person to another or by contaminated objects (e.g. clothes, hats, hairbrushes), and generally cause long-lasting infection with mild inflammation. Zoophilic dermatophytes primarily infect animals, although they can occasionally spread to humans by direct contact. Finally, geophilic dermatophytes grow in keratin-rich soil containing decaying feathers, horns, and hairs. Human infection by zoophilic and geophilic dermatophytes is less common and causes more severe, inflammatory tineas.
What are the signs and symptoms of a dermatophyte infection?
Signs and symptoms of dermatophyte infections vary depending on the infectious microorganism, affected area, and the severity of the infection. Most infections tend to be superficial and localized to a specific part of the body, such as the feet, scalp, or nails. However, the simultaneous presence of more than one type of tinea is common, and can occur from direct spreading from one area to another. In addition, tinea infections can become complicated by secondary bacterial infections, which occur when different opportunistic bacteria infect the lesions caused by dermatophytes.
Tinea corporis, also known as ringworm, typically presents with a round, red, itchy rash that has an inflamed, scaly border. These lesions tend to grow in an outward pattern creating a characteristic ring-like appearance, hence the name “ringworm”. Healthy individuals typically present with one or more of these lesions, whereas individuals with a decreased immune response are at risk of developing more invasive and widespread infections.
Majocchi’s granuloma, also known as fungal folliculitis, is a rare form of tinea corporis that occurs when dermatophytes penetrate the skin through damaged hair follicles, causing a deep skin infection. In otherwise healthy individuals, Majocchi’s granuloma presents with small skin lesions and inflamed hair follicles in areas that are prone to trauma, such as the legs, arms, and ankles. Meanwhile, individuals with a decreased immune response may present with more severe manifestations, such as deep subcutaneous plaques and nodules.
Tinea capitis, tinea faciei, and tinea barbae
Tinea capitis can either be inflammatory or non-inflammatory, depending on the causative microorganism. Inflammatory tinea capitis can present with a pus-filled lump on the scalp that may leave a localized area of scarring and permanent hair loss. On the other hand, non-inflammatory tinea capitis can present with itchiness, scaling, and reversible hair loss.
Tinea faciei affects the facial skin and can sometimes occur from direct spreading of a scalp infection, especially in children. It generally presents with a skin rash that worsens after sunlight exposure. Additionally, tinea barbae affects the hair follicles and skin of bearded individuals, and can present with areas of increased redness, scaling, and pus-filled lesions.
Tinea pedis and tinea manuum
Tinea pedis, also known as athlete's foot, presents with areas of scaling as well as the softening and breaking of the skin in the spaces between the toes and the soles of the feet. Less frequently, tinea pedis can present with erosions and painful open sores in between the toes.
Tinea manuum can occur in individuals with tinea pedis due to direct spreading of the infection from the feet to the hands. It typically presents with dry skin in the palms of the hands and a skin rash with inflamed, scaly borders on the back of the hand.
Tinea unguiumDermatophyte nail infections, or tinea unguium, can cause white or yellow discoloration of the nails, as well as either thickened or brittle nails. Severe nail infections can cause complete breakdown of the nail itself, which can then become separated from the nailbed. Generally, toenails are more often affected than fingernails, and individual nails are sometimes spared.
How do you diagnose a dermatophyte infection?
A dermatophyte infection is often suspected with clinical presentation of corresponding lesions or inflammation. In most cases, diagnosis can be confirmed by additional diagnostic tests, including direct microscopy, fungal cultures, or Wood’s light examination. Direct microscopy is typically performed with a potassium hydroxide (KOH) preparation that allows the branching filaments of the fungi (hyphae) to be seen under the microscope. Wood’s light examination uses ultraviolet light to detect areas of green fluorescence that may be caused by certain types of dermatophytes. Finally, a skin biopsy may be performed if the diagnosis is still uncertain or in the case of persisting lesions that have not resolved with prior treatments.If a dermatophyte infection is initially misdiagnosed for a similar skin condition and mistakenly treated with topical corticosteroids, the characteristic appearance of the tinea can be masked (i.e. tinea incognito). This can make the diagnostic process more difficult and may delay necessary treatment.
How do you treat a dermatophyte infection?
In otherwise healthy individuals, most dermatophyte infections are not considered serious. Mild forms of localized dermatophyte infections of the skin can be treated with topical antifungals, such as clotrimazole. Because topical treatments are unable to penetrate the scalp, tinea capitis often requires the use of oral antifungal medications, such as griseofulvin or terbinafine. In addition, individuals with a decreased immune response or those with inflammatory or widespread tineas may also require systemic treatment with oral antifungals in order to resolve the infection. Severe or persistent dermatophyte nail infections can also be treated with chemical or surgical removal of the affected nails.
To prevent the spreading of an infection, individuals should avoid close contact with others, as well as sharing personal objects that could be contaminated.
What are the most important facts to know about dermatophyte infections?
Dermatophyte infections are common superficial fungal infections caused by dermatophytes; a group of fungi that infect keratinized tissues, such as the skin, hair, and nails. Dermatophyte infections are classified according to the site of infection, and include tinea corporis (ringworm), tinea capitis (scalp ringworm), tinea unguium (nail infection), and tinea pedis (athlete's foot), among others. A characteristic feature of dermatophyte infections is a round, itchy rash with inflamed borders and a central clearing, commonly known as ringworm. Dermatophyte infections can be suspected with clinical presentation of the characteristic lesions, although diagnosis is typically confirmed by additional diagnostic tests, including direct examination under a microscope, Wood’s light examination, or fungal cultures. Treatment of dermatophytosis depends on the infectious microorganism, location and severity of the infection, and typically includes systemic or topical therapy with antifungals. Preventive measures to control the spread of the infection include avoiding close contact with others, as well as avoiding the sharing of personal objects that could be contaminated.
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Resources for research and reference
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