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SUPERFICIAL FUNGAL INFECTIONS

Nondermatophytes: Tinea versicolor/Pityriasis versicolor

  • Organism: Malassezia species (particularly Malassezia furfur and Malassezia globosa) (Fig. 19-1)

    • These dimorphic organisms are normal skin commensals (also known as Pityrosporum species), but become overgrown and assume mycelial forms to yield disease

    • Factors involved in the development of pathologic states include genetic predisposition, environmental conditions, and disorders of homeostasis

  • Clinical: hypopigmented and hyperpigmented scaly plaques with fine scale upon neck, trunk, and proximal extremities; occasional an inverse forms will affect flexural areas of the body

    • Hypopigmentation is caused by elaboration of tyrosinase inhibitors

    • Hyperpigmentation is caused by enlargement of melanosomes

    • The organism uses skin oils as an energy substrate; lesions are concentrated in "sebum-rich" areas of the body

    • Occurrence prior to adrenarche is uncommon due to low sebum production

    • Lesions typically have a fine, "bran-like" scale that accentuates with skin stretching

  • Diagnosis:

    • Wood's lamp: yield coppery-orange fluorescence in many cases (not all)

    • Potassium hydroxide (KOH) prep: "spaghetti and meatballs" appearance of hyphae and spores

    • Histology: round to oval yeast with short hyphae in stratum corneum

    • Culture: Sabouraud dextrose agar (SDA) with olive oil (fatty acids are required for growth); rarely utilized

  • Treatment:

    • Topical management: selenium sulfide, azole and allylamine antifungals, sodium sulfacetamide, ciclopirox olamine

    • Oral management: ketoconazole, fluconazole, and itraconazole

    • Oral terbinafine: some reports describe a poor clinical response

FIGURE 19-1

Tinea versicolor. (Used with permission from Dr. Asra Ali.)

Tinea nigra

  • Organism: Hortaea werneckii (formerly Exophiala werneckii or Phaeoannellomyces werneckii)

    • The species is a dematiaceous (melanin-producing) yeast that inhabits the soil of tropical and subtropical climates and it has remarkable halotolerance (salt tolerance)

  • Clinical:

    • Brown to black, flat, patches upon the palm or sole, caused by traumatic inoculation

    • Most often the lesions are asymptomatic, pruritus may be described on occasion

    • Classically the lesions may be confused clinically with nevi or melanoma

  • Diagnosis:

    • Histology: brown, septate hyphae in the stratum corneum without a host response, accentuates with periodic acid–Schiff (PAS) or Grocott's methenamine silver (GMS), marks with Fontana-Masson stain due to melanin

    • KOH prep: branched, septate hyphae with a brown color

    • Culture: SDA, brown-black colonies (due to melanin production)

  • Treatment:

    • Topical antifungals: ketoconazole, miconazole, ciclopirox olamine, terbinafine

    • Other: topical application of thiabendazole suspension has been successfully used

    • Systemic therapy: not usually required or recommended, oral itraconazole has been used successfully in some cases

Piedra

  • Organism:

    • Black piedra: Piedraia hortae

    • White piedra: Trichosporon asahii (formerly Trichosporon beigelii), sometimes also caused by Trichosporon ovoides, Trichosporon inkin, Trichosporon mucoides, Trichosporon asteroides, or Trichosporon cutaneum

  • Clinical:

    • The word piedra means "stone," both conditions yield concretions of fungi that resemble stones

    • Black piedra: hard, firmly adherent, pigmented nodules upon the hair shaft of the scalp, common in tropical climates

    • White piedra: soft, less adherent, white to light-brown ...

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