Dermatophyte infections

Dermatophyte infections, also known as tinea, are the most common fungal infections of the skin, hair, and nails. The term “dermatophyte” refers to fungal species that infect keratinized tissue, and includes members of the Trichophyton, Microsporum, and Epidermophyton genera. Tinea are classified based on their location (e.g., tinea pedis occurs on the feet and tinea capitis on the scalp). Children and immunocompromised individuals are more likely to contract tinea infections, especially tinea capitis. However, people of all ages may suffer from tinea pedis or tinea unguium. The clinical features of dermatophyte infection include pruritus, scaling, and erythema. The best initial test for the diagnosis of dermatophyte infection is potassium hydroxide (KOH) preparation, which allows segmented hyphae to be seen on microscopy. Generally, the treatment for dermatophyte infections is topical antifungals. Oral antifungals (e.g., terbinafine, griseofulvin) are always used in tinea capitis and are also used for severe, refractory cases of other kinds of tinea. Concomitant tinea infections in household members or pets should be treated as well.

Tinea versicolor, despite its name, is not caused by dermatophytes and is discussed in another article.

General ^[1]

• Definition: skin, hair, and nail infections caused by dermatophytes
• Pathogen
  • Dermatophytes are fungi that infect keratinized tissue and belong to the Trichophyton (most common), Microsporum, and Epidermophyton genera.
  • The most common causative pathogen of tinea is Trichophyton rubrum
• Risk factors
  • Diabetes mellitus
  • Immunocompromise (e.g., HIV)
  • Poor circulation, peripheral arterial disease
  • Maceration of skin (e.g., in athletes)
• Location
  • Scalp: tinea capitis
  • Bearded skin areas: tinea barbae
  • Body: tinea corporis
  • Hands: tinea manuum
  • Nails: tinea unguium
  • Inguinal area: tinea cruris
  • Feet: tinea pedis
• Clinical features
  • Erythematous plaques
  • Pruritus

Diagnosis of dermatophyte infections

• Best initial test: KOH preparation, possibly with fungal stain, showing branching segmented hyphae ^[2]
• Confirmatory test: fungal culture ^[3]
• Wood light: blue-green fluorescence of Microsporum species ^[1]

Treatment of dermatophyte infections

• Topical antifungals
  • Indication: dermatophyte infections other than tinea capitis
  • Agents: e.g., terbinafine; (1% for 1 week), azoles, allylamines, butenafine, ciclopirox, tolnaftate, undecanoate
• Systemic antifungal therapy
  • Indications
    • Tinea capitis
    • Failed topical treatment
    • Immunocompromised patients
    • Extensive spread
    • Some cases of tinea unguium
  • Agents: terbinafine, itraconazole, fluconazole, griseofulvin
• Chemical and surgical treatments for onychomycosis
  • Chemical removal of nail (e.g., with high dose urea or potassium iodide)
  • Surgical removal of the nail is indicated if systemic therapy is not effective.
• Other measures
  • Examination and treatment of symptomatic household members
  • Avoid close personal contact and sharing of potentially contaminated objects (e.g., shoes, combs) should be avoided to prevent the infection from spreading.

Because topical treatments are unable to penetrate the hair shaft, systemic therapy with oral antifungals such as griseofulvin or terbinafine is necessary for tinea capitis.

To prevent tinea infections from spreading, contaminated objects should not be shared (e.g., shoes, combs). Other members of the household and pets who are infected should also receive treatment.

Tinea capitis

• Definition: dermatophyte infection affecting the head and scalp
• Epidemiology: mainly occurs in children
• Pathogen: Trichophyton tonsurans (most common), Microsporum canis, Microsporum audouinii
• Clinical presentation
  • Round, pruritic scaly plaques with broken hair shafts or alopecia in affected areas
  • May mimic seborrheic dermatitis
  • Kerion: severe form of tinea capitis characterized by a deep, boggy plaque with pustule formation
  • Postauricular lymphadenopathy
• Diagnosis and treatment: See “Overview” section.
• Prognosis
  • Usually good
  • Hair regrows completely
  • Protracted infection and kerion may result in permanent alopecia.

Favus

• Definition
  • Chronic infection caused by Trichophyton schoenleinii
  • Severe form of tinea capitis
• Epidemiology: more common in Africa, the Middle East, and the Mediterranean
• Clinical presentation: formation of yellow, malodorous crust with subsequent scarring alopecia
• Treatment
  • Oral griseofulvin
  • Additional topical antimycotic agents

Tinea barbae ^[4]

• Definition: dermatophyte infection affecting bearded skin areas
• Epidemiology
  • Relatively uncommon
  • Most commonly affects farmers
• Pathogen: : most commonly Trichophyton verrucosum and Trichophyton mentagrophytes, which are transmitted from animals to humans
• Clinical presentation: erythematous papules, patches, and pustules, and crusting around the hair (kerion-like plaques)
• Diagnostics and treatment: See “Overview” section.
• Differential diagnoses: bacterial folliculitis, perioral dermatitis, pseudofolliculitis barbae, contact dermatitis, herpes simplex, acne vulgaris, acne rosacea

Tinea corporis (ringworm)

• Definition: dermatophyte infection affecting a location other than feet, scalp, nails, and groin; mostly the arms and upper body.
• Predisposing factors
  • Contact with infected individuals or animals
  • Moist environments (e.g., public swimming pools)
• Pathogen: most commonly T. rubrum
• Clinical presentation ^[5]
  • Initially round, pruritic, erythematous plaque that grows centrifugally
  • Develops into round, pruritic plaque with central clearing and a scaling, raised border
• Diagnosis and treatment: See “Overview” section.

Tinea cruris (jock itch)

• Definition: fungal infection of the inguinal area
• Pathogen: most commonly T. rubrum
• Clinical presentation
  • Pruritic erythematous plaque that grows centrifugally
  • Similar to tinea corporis but often without central clearing
  • Scaling, raised border
  • Spares the scrotum
• Diagnosis and treatment: See “Overview” section.

Tinea pedis (athlete's foot)/tinea manuum

• Definition
  • Tinea pedis: dermatophyte infection of the foot
  • Tinea manuum: dermatophyte infection of the hand
• Epidemiology
  • Affects adults and adolescents
  • Most common tinea infection
• Predisposing factors
  • Closed, tight footwear
  • Public showers
• Pathogen: most commonly T. rubrum, Trichophyton interdigitale
• Clinical features by type
  • Interdigital (most common): chronic, pruritic, erythematous scaling and erosions between the toes/fingers
  • Moccasin: hyperkeratotic thickening of the skin on soles of feet
  • Vesicular: pruritic or painful vesicular lesions and erythema, often on the medial foot
• Diagnosis and treatment: See “Overview” section.
• Complication: secondary bacterial superinfection (e.g., erysipelas)
• Prevention
  • Foot powders
  • Open shoes in warm, humid weather
  • Antifungal treatment of shoes
  • Footwear for public showers

Tinea unguium (onychomycosis)

• Definition: fungal infection of the nail
• Pathogen
  • Dermatophytes, most commonly T. rubrum (referred to as tinea unguium)
  • Yeast and molds (referred to as onychomycosis) ^[6]
• Clinical presentation: discolored (white, gray, or yellow) and brittle nails
• Diagnosis and treatment: See “Overview” section.

The successful treatment of onychomycosis involves not only the elimination of sources of infection, but also the promotion of personal hygiene, the disinfection of footwear, and the elimination of predisposing factors.

• Impetigo
• Seborrheic dermatitis
• Tinea versicolor
• Herald patch (pityriasis rosea)
• Cutaneous candidiasis
• Erythrasma
• Contact dermatitis
• Psoriasis

The differential diagnoses listed here are not exhaustive.