Dermatophyte Infections

Key Features

• Dermatophytes become attached to the superficial layer of the epidermis, nails, and hair, where they proliferate

• Fungal infection should be suspected with any red and scaly lesion

• Classified into tinea capitis, tinea corporis, tinea cruris, tinea pedis, tinea unguium

Clinical Findings

• Tinea capitis

  • Thickened, broken-off hairs with erythema and scaling of underlying scalp are the distinguishing features

  • Hairs are broken off at the surface of the scalp, leaving a "black dot" appearance

  • Diffuse scaling of the scalp and pustules are also seen

  • A boggy, fluctuant mass on the scalp called a kerion, represents an exaggerated response to the organism

• Tinea corporis

  • Presents either as annular marginated plaques with a thin scale and clear center or as an annular confluent dermatitis

• Tinea cruris

  • Symmetric, sharply marginated lesions in inguinal areas

• Tinea pedis

  • Presentation is with red scaly soles, blisters on the instep of the foot, or fissuring between the toes

• Tinea unguium (onychomycosis)

  • Loosening of the nail plate from the nail bed (onycholysis), giving a yellow discoloration, is the first sign of fungal invasion

  • Thickening of the distal nail plate then occurs, followed by scaling and a crumbly appearance of the entire nail plate surface

  • Usually only one or two nails are involved

Diagnosis

• Tinea capitis

  • Causative organisms: Microsporum canis and Trichophyton tonsurans

  • Fungal culture should be performed in all suspected cases

• Tinea corporis

  • Causative organisms Trichophyton mentagrophytes, Trichophyton rubrum, and M canis

  • Diagnosis is made by scraping thin scales from the border of the lesion, dissolving them in 20% potassium hydroxide (KOH), and examining for hyphae

• Tinea cruris: causative organisms are T rubrum, T mentagrophytes, and Epidermophyton floccosum

• Tinea pedis

  • Causative organisms: T rubrum and T mentagrophytes

  • Diagnosis is more common in the prepubertal child, although still most commonly seen in postpubertal males

• Tinea unguium

  • Causative organism: T rubrum

  • Diagnosis is confirmed by KOH examination and fungal culture

Treatment

• If hair is involved, systemic therapy is necessary

  • Griseofulvin (20 mg/kg/d; maximum 500 mg/dose) and terbinafine (62.5 mg/d, < 20 kg–125 mg/d, 20–40 kg–250 mg/d, > 40 kg) are both effective

  • Terbinafine does not work for M canis

• For nails, daily administration of topical ciclopirox 8% (Penlac nail lacquer) can be considered, as can terbinafine for 6–12 weeks or pulsed-dose itraconazole (50 mg/twice a day < 20 kg–100 mg/twice a day, 20–40 kg–200 mg/twice a day, > 40 kg) given in three 1-week pulses separated by 3 weeks

• Tinea corporis, tinea pedis, and tinea cruris

  • Can be treated effectively with topical medication after careful inspection to make certain that the hair and nails are not involved

  • Recommended agents: any of the imidazoles, allylamines, benzylamines, or ciclopirox applied twice daily for 3–4 weeks