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Dermatophyte Infections

The dermatophytes metabolize the keratin of the skin, hair, and nails. Hydration and occlusion of the skin facilitate infection. Although dermatophyte infections routinely affect persons who are otherwise healthy, immunocompromised patients are particularly susceptible.

Diagnostic Evaluation of Dermatophyte Infections

Potassium Hydroxide Exam. Accurate diagnosis of dermatophyte infections requires a potassium hydroxide (KOH) examination. Scrapings from involved skin or nail are placed in a drop of 20% potassium hydroxide (KOH) solution on a glass slide; a coverslip is applied, and the preparation is heated gently over an alcohol lamp. Examination under a microscope reveals the septate, branching, threadlike hyphae characteristic of dermatophytes. KOH examination of hair reveals small spores. If potassium hydroxide exam is negative, the scales may be cultured on a fungal medium.

Tinea Pedis (athlete's foot)

The acute form of tinea pedis is characterized by Treatment of Dermatophyte Infections, ringworm ring worm, tinea sudden onset of an erythematous vesicular or bullous eruption, which is intensely pruritic and sometimes painful. It occurs interdigitally and on the soles of the feet. Acute attacks are self-limited, but recurrences are common. A sterile vesicular "id eruption" sometimes appears.

The chronic form of tinea pedis is Interdigital fissures are common. Untreated, the eruption persists indefinitely. The palm on the dominant-handed side is often similarly involved ("one-hand, two-feet disease").

Tinea pedis is caused by Trichophyton mentagrophytes or Trichophyton rubrum. KOH examination of skin scrapings show septate hyphae.

Management of Tinea Pedis

Acute disease usually can be managed with a topical antifungal. Azole creams (eg, ketoconazole [Nizoral], sulconazole [Exelderm]), allylamine creams (eg, terbinafine [Lamisil]), and ciclopirox (Loprox) are all equally effective. These agents should be applied twice daily.

For refractory cases, oral griseofulvin microsize (Fulvicin U/F, Grifulvin V, Grisactin) in a single daily dose of 500 mg for 4 to 8 weeks may be prescribed. Itraconazole (Sporanox), 200 mg twice daily for 7 days, and terbinafine (Lamisil), 250 mg daily for 14 days.

Onychomycosis (tinea unguium)

Onychomycosis affect the fingernails and toenails. Nail lesions of psoriasis, eczematous eruptions and ischemic arterial disease can mimic onychomycosis. The KOH test or a culture.

Onychomycosis is cause by T rubrum, and some degree of tinea pedis is usually also present. The disease usually begins at the corner of the nail as a yellowish discoloration. As it spreads, the nail begins to separate from its bed distally, resulting in irregular nail dystrophy.

Management of Onychomycoses

The presence of the fungus in the nail or its bed is confirmed by KOH examination or culture.

Topical treatment is ineffective. Results with griseofulvin by mouth have been disappointing, but response to newer antifungals has been excellent. Itraconazole and terbinafine.

Itraconazole (Sporanox)

Toenail infection with or without fingernail involvement: 200 mg (2 capsules) by mouth daily for 90 days. Pulse therapy, 200 mg (2 capsules) bid for 1 week per month for 4 months. Itraconazole should be taken with a full meal.

Fingernail infections: Pulse therapy, 200 mg (2 capsules) bid for 1 week per month for 2 months.

Drug interactions. The medication is contraindicated in patients taking astemizole (Hismanal) and cisapride (Propulsid) because serious cardiovascular events may occur. Itraconazole also should not be used with triazolam (Halcion), midazolam (Versed), lovastatin (Mevacor), or simvastatin (Zocor).