Section 21. Cutaneous Fungal Infections

Cutaneous fungal infections are categorized as follows:

1. 1. Superficial: infecting the stratum corneum, hair, and nails.

• The three major genera are Trichophyton, Microsporum, and Epidermophyton. The term “tinea” is used to denote fungal infection and is typically modified by site (e.g., tinea capitis, tinea corporis).
• Candida is a normal inhabitant of the oropharynx and gastrointestinal tract. Moist, wet conditions favor Candida overgrowth and can lead to superficial infection of the skin.

1. 2. Deep: involving the dermis and subcutaneous tissues.

• Subcutaneous mycoses are the result of implantation and include chromoblastomycoses, mycetoma, sporotrichosis, basidiobolomycosis, and lobomycosis.

Deep mycoses are the result of hematogenous spread or extension from an underlying structure. True pathogens infect hosts with normal immunity and include histoplasmosis, coccidioidomycosis, and paracoccidioidomycosis. Opportunistic pathogens infect immunocompromised hosts and include disseminated candidiasis and aspergillosis.

Tinea Capitis

Tinea capitis is a fungal infection (Microsporum or Trichophyton) of the scalp and hair characterized by follicular inflammation with painful, boggy nodules that drain pus and result in hair loss.

Insight

If there is any doubt about the diagnosis, a fungal culture of affected hairs and scale can be very helpful. If systemic treatment is given without improvement, the initial diagnosis is called into question, but culture after treatment is extremely low-yield.

Synonym Scalp ringworm.

Epidemiology

Age Children: 2 to 10 years; rarely seen in infants or adults.

Gender M > F, 5:1.

Race Blacks > whites.

Incidence Most common fungal infection in childhood. Eight percent of the pediatric population.

Etiology Trichophyton tonsurans (90%) in the United States and West Europe. > Microsporum canis > M. audouinii > T. verrucosum. T. violaceum > T. tonsurans in Southeast Europe and North Africa.

History

Two to four days after exposure, scaly pruritic patches appear in the scalp with hair loss. Untreated, the lesions enlarge. Systemic symptoms may include cervical lymphadenopathy, malaise, or fever. Additionally, a systemic allergy to fungal elements can be seen (see “Tinea and Id Reaction”).

Physical Examination

Skin Lesions

1. 1. Ectothrix (infection on the outside of the hair shaft).

   a. Gray patch ringworm. Brittle hair; shafts break off close to scalp surface. Caused by M. audouinii and M. canis (Fig. 21-1).

   2. Endothrix (infection on the inside of the hair shaft).

   a. Black dot ringworm. Broken-off hairs give appearance of black dots, caused by T. tonsurans and T. violaceum (Fig. 21-2).

   b. Kerion. Boggy, purulent, inflamed painful nodule drains pus. Hairs do not break but fall out easily. Heals with residual hair loss (Fig. 21-3).

   c. Favus. Scutula (yellowish crusts) are ...