Dermatophytic fungal infections are usually caused by dermatophyte infections, mainly tinea pedis, tinea corporis, tinea cruris, tinea capitis and tinea nail. Recently, Dr. Clinard et al. from Campbell University published a review on dermatophyte infections in the U.S. Pharmacist journal, which focuses on the types, diagnosis and treatment of dermatophyte infections to help medical professionals identify the most common fungal infections and understand the most effective treatment options for clinical treatment and prevention.
In general, because dermatophyte fungal infections require keratin to sustain growth, the disease is confined to the cuticle, finger (toe) nails, and hair shaft. The most common causative agent of dermatophytic fungal infections is Tinea capitis, but they can also be caused by non-dermatophytic fungi and yeast infections and are classified as tinea pedis, tinea corporis, tinea cruris, and tinea capitis depending on the site of infection.
Dermatophyte infections are most commonly transmitted by direct human-to-human contact, but can also be transmitted through contact with animals, soil, and pollutants. Patients who are susceptible to dermatophytic fungal infections include those who are obese, immunodeficient, immunosuppressed and have impaired circulatory function. In addition, prolonged exposure to sweaty clothing and bedding, poor hygiene, and living in warm, humid climates can increase the risk of fungal infections.
The typical skin lesion of a fungal skin infection is a well-centered, red patch with mobile edges and a phosphorous flake, often referred to as “ringworm”. One of the key points in identifying dermatophyte infections is the site: ringworm infections do not involve the mucous membranes. Despite its typical presentation, ringworm infection may still present similarly to many other dermal diseases, leading to misdiagnosis and failure to receive effective treatment.
Types of infections
1. Tinea pedis
Tinea pedis is the most common dermatophyte fungal infection, commonly known as “foot fungus,” which infects approximately 20 million people each year in the United States, with an incidence of approximately 70％. Tinea pedis is clinically classified into four types based on the morphology of the lesions, and there is sometimes overlap between the different types.
The most common type is the vesicular type, which is mainly characterized by chapped, flaky lesions, or maceration at the intersection of the fingers (toes), malodor, itching, and tingling sensation. Fungal infections often involve the lateral aspect of the toes and may extend to the sole or dorsum of the foot. Warm, humid environments can worsen the lesions.
The second type is the chronic papulosquamous type, which often appears on both feet and mainly presents as mild inflammation with scattered scales on the plantar skin.
The third type consists of blisters or purulent blisters appearing on the plantar and metatarsal surfaces and is called the blister type. Scales may be found on the lesions. The fourth type mainly presents with maceration of the plantar skin, exposed lesions, and vesicular oozing, often accompanied by an odor. This type is often combined with opportunistic gram-negative bacterial infections.
Adults are more likely to develop tinea pedis than children due to higher exposure. People who use public swimming pools or bathing facilities are at increased risk for tinea pedis; in addition, people involved in high-intensity activities that cause chronic foot trauma and those who wear poorly ventilated footwear are also prone to tinea pedis.
2. Tinea corporis
Tinea corporis can occur on any part of the body except the scalp, hair, hands, feet, and nails. The lesions often appear as small, ring-shaped erythematous plaques with scales that have clear borders and are constantly expanding outward, with the center gradually fading and blistering or pustules appearing. Animal-friendly dermatophytes tend to invade exposed skin, while human-grown dermatophytes infect impermeable or traumatized areas.
3. Ringworm of the femur
Tinea cruris is a fungal skin infection that appears in the upper mid-thigh and groin area, more often in men than women, and usually does not affect the scrotum. It is often characterized by excessive dampness, itching, and burning sensations. Risk factors for ringworm include tinea pedis, obesity, diabetes, and immunodeficiency.
4. Tinea capitis
Tinea capitis is a fungal infection of the scalp and hair resulting in a disease that most often occurs in children who come into contact with other children or pets. There are three types of ringworm of the head: tinea nigra (spot), tinea alba and tinea aureus. Trichophyton rubrum breakage often results in tinea nigra, endemic tinea albicans is caused by Microsporum canis infection and is usually transmitted by dogs and cats, and tinea aureus is characterized by spores, bubbles, and broken hyphae.
Tinea nigra (spot) is often asymptomatic when it starts. Erythematous, scaly patches on the scalp gradually enlarge and baldness develops; hair breaks off at the patches and appears as “black spots”. If tinea nigra is left untreated, baldness and scarring may persist. Sometimes, the lesions change, gradually swelling and softening to inflammatory nodules known as ‘pustular lichen’. Tinea suppurativa forms as a result of the body’s immune response to the fungus. Pustular lichen may present with enlarged lymph nodes. Tinea albuginea presents as ring-shaped scaly patches. Tinea suppurativa may be complicated by Tinea albicans.
Since topical treatment cannot penetrate the hair shaft, systemic antifungal treatment of tinea capitis is necessary. Antifungal shampoos may be recommended as an adjunctive treatment. Asymptomatic carriers of dermatophytes may be a source of reinfection, and sharing of contaminants such as hats, combs, and brushes should be avoided.
5. Nail fungus
Nail fungus, commonly known as gray nails, is most commonly caused by dermatophyte infections, but non-dermatophyte and Candida spp. fungal infections can also cause nail fungus. More than 25 million people in the United States develop onychomycosis each year. Infected fingernails tend to become thin, yellow, rough, opaque, and brittle. The nail may detach from the nail bed and the dermal tissue around the infected nail may become hyperkeratotic. Risk factors for onychomycosis include diabetes, trauma, family history, tinea pedis, smoking, prolonged water exposure and immunodeficiency.
6. Ringworm difficult to recognize
Ringworm difficult to recognize is a dermatophyte infection whose borders may have disappeared due to hormonal treatment, while the ringworm is more diffuse in size. Diagnosis of ringworm difficult to recognize requires a thorough patient history; cases where the rash has been treated with hormones in the past and the rash appears to disappear but then recurs should be considered as possible ringworm difficult to recognize.
7. Candida spp. fungal infection
Candida is a normal colonizing organism in the body, but it is also a common fungal infection pathogen; acute infection may occur when the balance of normal colonizing organisms is disturbed. Risk factors for Candida infection include the use of antibiotics, steroid hormones, diabetes, obesity, immunosuppression, and immunodeficiency. In addition, a warm, moist environment helps Candida to grow. Candida infections often present as red lesions with papules and pustules, and the common sites of infection are the oral and genital areas.
Treatment
1. Local treatment
In general, tinea pedis, tinea corporis, and tinea cruris respond better to topical treatment. Most topical medications are over-the-counter, mainly ointments, creams, powders, and sprays, and are well tolerated with few reported adverse reactions such as skin irritation, burning sensation, itching, or dryness, and there are few drug interactions when topical medications are used.
A variety of combinations of antifungal drugs and steroid hormones are currently available on the market, but current clinical guidelines do not recommend antifungal drugs in combination with hormone therapy. Although combinations have clinical efficacy, the quality of studies related to them is not ideal, mainly because of lack of precision, bias, and the inability to assess relapse rates.
Patient compliance may influence drug selection, therefore, appropriate drugs should be selected based on the patient’s daily habits and activities as well as the patient’s individual circumstances, such as comorbidity status, age, and drug sensitivity.
2. Oral treatment
Oral medication may be recommended if tinea pedis, tinea corporis, or tinea corporis spreads, worsens, or is refractory. Oral treatment of tinea nail is more effective than topical treatment. Among them, ringworm of the head must be treated with oral medication because topical treatment cannot penetrate into the hair shaft.
3.Non-medication treatment
Good skin care, including regular bathing and keeping the skin dry, is the basis for preventing fungal skin infections, and care should be taken to avoid prolonged exposure of the infected area to moisture. To prevent the recurrence of tinea pedis, walking barefoot in public bathrooms and showers should be avoided. Patients with tinea capitis should consider wearing breathable shoes and absorbent socks, and using powders to control humidity.
Once tinea capitis is diagnosed, all contaminated combs, brushes, hats, and beds should be cleaned. Children with tinea capitis can return to school once treatment has been started, but public grooming tools, hats, and bedding need to be disabled for a minimum of 2 weeks.
Summary
Accurate diagnosis and treatment of fungal skin infections is still a major health concern. Clinicians should be aware of the need to effectively control dermatophyte infections with pharmacologic and nonpharmacologic treatments and to select appropriate medications based on patient characteristics and lifestyle differences.