Fungal Infections of the Skin

Fungal Infections

• Fungal infections can be classified into two types: superficial and deep (systemic) infections.
• Superficial infections are restricted to the skin and its appendages, while deep infections are usually systemic in nature with occasional involvement of the skin.

Causes of Fungal Infections

• Fungal infections can be caused by:
  • Dermatophytes (e.g. microsporum, trichophyton, and epidermophyton)
  • Yeasts (e.g. malassezia furfur and candida albicans)
• Source of infection:
  • From human (anthropophilic species)
  • From animals (zoophilic species)
  • Rarely, from soil (geophilic species)

Yeast-Mycelial (Y-M) Shift

• The fungus changes from a budding yeast (Y) phase to a mycelial (M) phase, leading to a shift from a commensal state to a pathogenic state.

Clinical Types of Dermatophyte Infections

• Classified according to the site of infection:
  • Tinea capitis (ringworm of the scalp)
  • Tinea corporis (tinea circinata)
  • Tinea barbae (ringworm of the beard)
  • Tinea cruris (ringworm of the groin)
  • Tinea pedis (ringworm of the feet)
  • Onychomycosis (fungal infection of the nails)

Tinea Capitis

• Mainly affects school children, more common in boys than girls.
• Main causative fungi in Egypt are Trichophyton violaceum and Microsporum canis.
• Clinical picture:
  • Scaly type: single or multiple scaly patches, often circular in shape, with numerous broken-off hairs.
  • Kerion (inflammatory type): caused by animal fungi, presented as boggy indurated swellings with crusting and loose hairs.
  • Black-dot type: bald patches with formation of black dots as the affected hair breaks at the surface of the scalp.
  • Favus: caused by Trichophyton schoenleinii, characterized by yellowish, cup-shaped crusts (scutula) and mousy odor.

Modes of Infection

• Direct contact with infected child
• Indirect: use of patient's fomites as brushes and caps

Diagnosis

• Clinical
• Wood's light (long-wave UVR passing through a glass containing nickel oxide)
• Direct microscopic examination of infected hair and scales using 10-20% KOH
• Culture on Sabouraud's medium

Treatment

• Topical treatment: little effect, includes Whitfield's ointment, imidazoles, and allylamines
• Systemic treatment:
  • Griseofulvin: 10 mg/kg/day for at least 6 weeks and 8 weeks in favus
  • Itraconazole, fluconazole, and terbinafine: only in selected cases

Tinea Corporis (Tinea Circinata)

• Commonly involves exposed skin, more common in children
• Clinically: circular, sharply circumscribed, erythematous, and scaly with active edge (elevated and more inflamed than center)
• Treatment: mild lesions, topical treatment for 2-4 weeks; extensive lesions, may require systemic antifungals

Tinea Barbae (Ringworm of the Beard)

• Mainly affects adults in contact with farm animals
• Lesion may be presented as kerion or tinea circinata, mostly unilateral
• Treatment: oral and topical antifungals

Tinea Cruris (Ringworm of the Groin)

• Mostly affects men on upper and inner surfaces of the thighs, especially in hot summer months
• Clinical picture: small erythematous, scaly patch that spreads peripherally and partly clears in the center, edge is well defined with papules, vesicles, or pustules
• Treatment: drying the lesions, specific topical, and oral antifungals

Tinea Pedis (Ringworm of the Feet)

• Most common fungal infection, more common in adult males
• Predisposing factors: wearing tight shoes, communal showers, swimming baths, and hyperhydrosis
• Clinical varieties:
  • Interdigital variety: peeling, maceration, and fissuring affecting lateral toe clefts
  • Squamous hyperkeratotic variety: very chronic and resistant to treatment, characterized by erythema and scaling
  • Vesiculobullous variety: acute vesicular or bullous eruption may involve entire sole
• Treatment: drying the feet thoroughly, antifungal powder on feet of susceptible persons, topical antifungals for mild cases, and systemic for extensive lesions

Onychomycosis (Tinea Unguium)

• Nail plate becomes thickened, discolored, and cracked with accumulation of subungual hyperkeratosis
• Treatment: oral antifungals, especially oral terbinafine, for 6 weeks in finger nails and for 12 weeks in toe nails

Pityriasis Versicolor

• Mild, chronic fungal infection caused by Malassezia furfur
• More common in tropical climates, with onset commonly in warmer months of the year
• Clinical picture: sharply demarcated macule covered by fine branny scales, may coalesce to form large confluent areas and scattered oval patches
• Treatment: topical antifungals, ketoconazole 2% shampoo, selenium sulphide 2-5% shampoo, and sodium hyposulphide 20% solution

Other Cutaneous Disorders Associated with Malassezia Yeasts

• Seborrheic dermatitis
• Atopic dermatitis
• Pityrosporum folliculitis
• Sebopsoriasis
• Confluent and reticulate papillomatosis

Candidiasis

• Causative fungi: Candida albicans (normal inhabitant at various sites as gut, mouth, and vagina) or other species of Candida
• Predisposing factors:
  • Warmth, moisture, and maceration of skin
  • Drugs: e.g. prolonged use of steroids, antibiotics, and immunosuppressives
  • Chronic debilitating diseases: e.g. DM, lymphoma, and carcinoma
  • AIDS
• Clinical manifestations:
  • Oral candidiasis (thrush): sharply defined patch of creamy, curd-like, white pseudomembrane
  • Perleche (angular stomatitis): maceration with transverse fissuring of the angles of the mouth
  • Candidal vulvovaginitis: labia are erythematous, moist, and macerated; cervix is hyperaemic, swollen, and eroded with some vesicles on its surface
  • Candidal intertrigo: in skin folds, especially in obese individuals
  • Napkin candidiasis: enhanced by maceration produced by wet diapers
  • Candidal paronychia: cushion-like thickening of paronychial tissue, erosions of lateral borders of nail, gradual thickening and discoloration of nail plates, with development of transverse ridges

Treatment of Candidiasis

• Topical nystatin
• Topical imidazoles
• Systemic treatment: with ketoconazole, fluconazole, and Itraconazole