Dermatophytosis

Are You Confident of the Diagnosis?

Dermatophytoses are superficial fungal infections that are typically limited to the upper layer of the skin. Dermatophytes subsist on keratin debris. At any one time 1 in 5 Americans is affected by a dermatophyte infection.

Dermatophytes are divided into three groups. Anthropophilic dermatophytes are restricted to human hosts and produce a mild chronic inflammation. These include Trichophyton rubrum, Trichophyton mentagrophytes, Epidermophyton floccosum and Trichophyton tonsurans. Zoophilic organisms are found mainly in animals and cause marked inflammation in humans with contact with infected dogs, cats, birds, farm animals (cattle, horses). These include Microsporum canis and Trichophyton verrucosum. Geophilic species can be found in the soil, but also in animals and humans, and cause significant inflammation that can lead to scarring. These include Microsporum gypseum.

Characteristic findings on physical examination

Tinea pedis, also known as “athlete’s foot,” is the most common presentation of a dermatophyte infection. Tinea pedis is dermatophyte infection involving the interweb spaces of the toes and the soles of the foot. It commonly presents as itchy scaly soles and itchy, fissured and macerated intertoe web spaces (Figure 1). Tinea pedis may be intertoe web space only. This type of infection presents with scaling, fissuring and maceration, particularly between the fourth and fifth toes. A second presentation is one of chronic thick hyperkeratotic scale and redness on the plantar surface of the feet.

Figure 1.

Tinea pedis may also present as inflammatory and blister-filled. This last presentation is often associated with an id reaction occurring on one or both hands. The least common presentation is one of ulceration. This can occur in the elderly or those with diabetes. Tinea manum is often a presentation of tinea pedis and is scaling and redness of one hand and two plantar surfaces. Often this is attributed to the transmission from the feet to the dominant hand by scratching and is known as “one hand two feet syndrome.”

Tinea cruris, also known as “jock itch,” is the second most common presentation of a dermatophyte infection. The most common clinical presentation is itchy, red, scaling patches in the intertriginous areas, which include the upper inner thigh, inguinal folds, perineal area and buttocks. Occasionally it will extend up on to the lower abdomen from the groin. The red scaly patches are usually bilateral.

Other details that are helpful include history of tight- fitting clothing, underwear or bathing suits and a hot humid environment. Multiple other diseases including intertrigo, inverse psoriasis, erythrasma, acanthosis nigricans can also occur in the folds. These can be distinguished by history and by performing fungal cultures or using potassium hydroxide to examine scraping as detailed below. Wood’s lamp examination is also helpful since erythrasma will fluoresce pink.

Tinea capitis is discussed in detail in the chapter entitled Tinea capitis/kerion.

Tinea corporis is a superficial dermatophyte infection that can affect any area of the body but typically excludes the glabrous skin of palms, soles, groin and scalp (Figure 2). It is typically inflammatory but can be non-inflammatory. On history you should be alert for pink or red plaques with a raised active border of scale. They can rapidly enlarge and over time the central area improves and clears leaving an annular plaque with a scaly border. Clinicians should pay special attention to symptoms, travel history, contacts with animals and other people. While infected patients have variable symptoms, itch and burning are common symptoms. Since tinea corporis occurs most commonly in hot humid environments it is important to elicit this from history.

Figure 2.

Since it can be passed from both humans and animals, exposure history through both travel and occupation should be evaluated for contact with infected humans or animals. Common exposures include people whose jobs have contact with animals (veterinarians, farmers, animal research technicians) and athletes who are involved in contact sports or have exposure to gyms.

A few clinical variants exists that are distinct. Tinea corporis gladiatorum occurs from skin-to-skin contact in wrestlers most commonly. Tinea imbricata is a form of tinea corporis that occurs in Southeast Asia and Central and South America and is clinically distinguished by concentric rings of erythema and scale. It is caused by Trichophyton concentricum. Majocchi’s granuloma is typically caused by Trichophyton rubrum and is a fungal infection in the hair follicles with a granulomatous reaction. Majocchi’s is discussed in more detail under unusual presentations below. The differential diagnosis of tinea corporis includes drug eruption, eczematous dermatitis, psoriasis, cutaneous lupus and secondary syphyllis.

Tinea unguium is a dermatophyte infection of the nail plate (Figure 3) and is a subset of onychomycosis, which may also be caused by yeast and nondermatophyte molds. It is one of the more resistant dermatophyte infections to treat and usually requires oral therapy. Thickening of the nail, brittleness of the nail, loosening or lifting of the nail can all be signs of dermatophyte infection in the nail plate. Yellow or white discoloration is also common.

Figure 3.

Tinea barbae/tinea faciei are dermatophyte infections of the face. Tinea barbae typically affects the bearded area of men and tinea faciei (Figure 4) can occur on any area of the face in women and children. These dermatophyte infections are the most commonly underdiagnosed or misdiagnosed. While they can occur as red patches or plaques on the face, they often do not have scale. They are often mistaken for contact or eczematous dermatitis, polymorphous light eruption, cutaneous lupus or other photosensitive disorders. Often they are treated with topical steroids, which can change the appearance of the primary lesions. See Tinea incognito below.

Figure 4.

Expected results of diagnostic studies

Diagnostic confirmation

Scraping scale from the border to look under light microscopy using potassium hydroxide (KOH) results in identification of fungal elements. The KOH helps to dissolve keratin and leave the fungal elements intact. Fungal culture is more specific than KOH for detecting a dermatophyte infection. If suspicion is high and KOH is equivocal or negative, a fungal culture should be performed.

Fungal cultures can be grown on a number of media. The most common ones are Sabouraud agar, which contains agar and glucose but no antibiotics, Mycosel, which contains agar and antibiotics and dermatophyte test medium (DTM). DTM contains phenol red solution, which causes a color change from yellow to bright red under alkaline conditions and indicates a positive dermatophyte result. Polymerase chain reaction ( PCR) can also be used for fungal DNA identification. Confirmation can also be made by skin or nail plate biopsy. Septate branching hyphae can often be seen in the stratum corneum using special fungal stains including periodic acid-Schiff or Gomori methenamine silver on biopsied specimens.

Who is at Risk for Developing this Disease?

Tinea pedis is thought to be more common in men. It is also more common in hot humid environment, with the prolonged use of occlusive footwear especially plastic or rubber footwear as well as in those who share shoes, share public showers or have an increased tendency to sweat. Tinea pedis is more common in certain families and there appears to be predisposition in some individuals.

Tinea cruris affects mostly men with a 4:1 male to female ratio and has a peak incidence in men in their teens to thirties. The exact incidence is not known since it is under-reported. Affected men include athletes, those whose jobs require tight-fitted uniform and those living in hot humid environments. Additionally, the obese and those with diabetes are at increased risk. Chronic use of oral steroids and chronic immunosuppression in general is also thought to be a risk. Children do not commonly develop tinea cruris. Although it is often noted that patients with tinea cruris also have tinea pedis or onychomycosis, there are no studies to confirm this as a risk factor.

Tinea corporis is more common in warm humid environments and occurs in all age groups. There is some evidence that women who have increased contact with children are at increased risk. Additionally those in occupations that put them in contact with animals, athletes and children are at slightly increased risk. Immunocompromised patients are at increased risk for more disseminated disease and atypical presentations.

Tinea unguium risk factors include older age, history of tinea pedis, diabetes and poor-fitting shoes.

Tinea barbae commonly affects men whereas tinea faciei affects all ages and both sexes with peak incidence in children and in adults in their 20s to 40s. The most common sources of infection in the United States are pets (primarily cats and dogs). Those in frequent contact with pets and farm animals are at increased risk as are those with increased contact with children. Tinea barbae used to be a more common infection when razors were used without sterilization on multiple clients in a barber shop, but since the common practices of sterilization and single-use blades, this is a less frequent infection.

What is the Cause of the Disease?

Etiology

At the national Centre for Mycology in Alberta, Canada, 58% of dermatophytes isolated are T rubrum, 27% are T mentagrophytes, 7% are T verrucosum and 3% are T tonsurans. In the United States there are higher percentages of T tonsurans isolated especially from tinea capitis. At the Center for Disease Control, the percentages for dermatophyte infections have not been estimated.

Tinea pedis is most commonly caused by T rubrum. Intertriginous and hyperkeratotic versions are typically caused by T rubrum. Bullous tinea pedis is more often caused by T mentagrophytes. E floccosum has also been reported to cause tinea pedis.

Tinea cruris is commonly caused by T rubrum or E floccosum.

Tinea corporis is most commonly caused by T rubrum ( some report it is responsible for close to 50% of all cases). There are increasing numbers caused by T tonsurans, T mentagrophytes and Microsporum canis. Rarer causes include T verrucosum, E floccosum and T violaceum.

Tinea unguium is most commonly caused by T rubrum, T tonsurans, T mentagrophytes, E floccosum.

Tinea barbae and faciei are commonly caused by M canis but have also been shown to be caused by T tonsurans, T rubrum and E floccosum. Rare cases can be caused by T schoenleinii.

Pathophysiology

All dermatophytes prefer to live in the cornified layers of the skin, which provide a warm, moist environment. Many dermatophytes invade in a centrifugal fashion. The epidermis proliferates as a defense and so the active edge of the infection is scaly and more inflammed while the central region has less scale.

Systemic Implications and Complications

Tinea infections in general do not have any systemic implications. They may be a sign of underlying diabetes or other immunosuppression but in the majority of cases it is just a result of having moist warm skin folds. No testing is necessary. Unusual presentations and extensive disease are most common in the immunosuppressed, so in a patient without a known history of immunosuppression and atypical presentation, HIV testing and appropriate cancer screening may be indicated.

Tinea faciei can result in scarring if infection is caused by T schoenleinii or zoophilic species. Scarring is a complication that can occur with tinea capitis as well, as discussed in the chapter on tinea capitis.

Treatment Options

Tinea pedis may be treated topically or orally. Topical medications include topical imidazoles, pyridones, allylamines and benzylamines 1 to 2 times a day for up to 6 weeks but most commonly up to 2 weeks. Clotrimazole, which is a broad-spectrum anti-fungal agent that alters cell membrane permeability and causes death of fungal cells. Ketoconazole is a broad-spectrum imidazole that inhibits synthesis of ergosterol and causes the cellular components to leak, also resulting in death of fungal cells. Econazole also has some antibacterial activity so can be used when a mixed infection is suspected. Ciclopirox 1% cream is a topical pyridone that interferes with synthesis of DNA, RNA and proteins.

Topical allylamines include naftifine 1% cream and terbinafine topical. These may be effective in as little as 1 week. Terbinafine should not be used for more than 4 weeks. Hyperkeratotic tinea pedis usually requires a topical keratinolytic agent like urea or salicylic acid to remove the scale and allow the topical antifungal medications to penetrate.

Patients with severe inflammatory or bullous tinea pedis and those with underlying chronic disease like diabetes usually require a short course up to 2 weeks of oral antimycotics. Itraconazole, terbinafine and fluconazole should be considered in these patients as oral antimycotics. Aluminum acetate (Domeboro, Burrow’s solution) can also be used as a drying agent for bullous tinea pedis. Tablets should be diluted to 1:10 to 1:40 in water. Additionally keeping feet dry, wearing breathable shoes and using moisture wicking socks should be part of a treatment plan. Patients should also be encouraged not to share socks and shoes and to wear flip flops or foot covering while at public showers or pools.

Tinea cruris is typically treated topically since it is a localized infection. Over-the-counter products are available and are effective. Butenafine hydrochloride 1% is the ingredient found in Lotrimin Ultra and can be used once a day for 2 weeks in those over 12 years of age. The imidazole class including clotrimazole, ketoconazole, econazole can also be used twice a day for 2 weeks. Terbinafine topically can also be used 1 to 2 times a day in those over 12 years of age for 1 to 2 weeks. It is uncommon to require oral antifungal medications. Additional treatment includes discontinuing tight-fitted clothing, providing air to occluded skin folds and proper cleansing of uniforms and clothing. Weight loss can be part of an effective therapy for those with recurrent infection because of excessive moist wet folds in the setting of obesity.

Tinea corporis is usually treated with topical therapy since it is localized infection. Topical azoles and allylamines are recommended two times a day for a minimum of 2 weeks and should be applied to the area affected and an additional 1 to 2mm beyond the visibly infected area. Ciclopirox olamine also may be used. There is debate about whether topical steroids should be added to the treatment regimen. Low-potency steroids are sometimes recommended to relieve itch and erythema; however, prolonged use can lead to recurrent or persistent infections. If used at all, topical steroids should only be used for the first few days of treatment. It is not recommended to use the combination steroid/antifungal agents.

Systemic therapy may be necessary for disseminated disease or in immunocompromised individuals. Griseofulvin at 10mg/kg/day dosing can be used for 4 weeks. Alternatively systemic azoles like fluconzaole can be given at 50 to 100mg/day or 150mg once a week for 2 to 4 weeks. Itraconazole can be given at 100mg/day for 2 weeks. Oral terbinafine can also be used at 250mg/day for 2 weeks. Dosing should be adjusted in children.

Tinea unguium is usually treated orally. Topical therapy has little role in infection of the nail plate. Mycologic cure rates for ciclopirox (Penlac) nail lacquer, applied daily for up to 48 weeks, have ranged from 29% to 47%. Itraconazole and terbinafine have been studied for tinea unguium and can be used for 12 weeks at 200mg once a day for itraconazole and 250mg once a day for terbinafine in adults. Dose adjustments should be made for children (4 to 5mg/kg/day of terbinafine has been used successfully). Hepatic function should be followed at baseline and every 4 to 6 weeks when on this therapy. Griseofulvin is not often used since some studies show it is ineffective and may require 12 months of therapy.

Tinea faciei can usually be treated with topical anti-fungal therapy. Tinea barbae, because it involves invasion of the dermatophyte into the hair follicle, requires short courses of 4 to 6 weeks of oral antifungal therapy as detailed below.

Optimal Therapeutic Approach for this Disease

Topical and oral treatments for dermatophytosis are summarized in Table I and Table II.

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