Superficial Mycoses Reviewer

Superficial Mycoses Reviewer

What are Superficial Mycoses?

Fungal infections limited to the keratinized outer layers of skin (stratum corneum), hair, and nails. They elicit little to no host immune response, are non-destructive and asymptomatic, usually cosmetic in concern, and are easy to diagnose and treat.

The 4 Superficial Mycoses at a Glance

1. Pityriasis (Tinea) Versicolor

Pathogen: Malassezia species (lipophilic yeast, normal skin flora)

Key species:

• M. globosa – most common causative species

• M. furfur – facultative pathogen; classic lab findings

• M. restricta – associated with seborrheic dermatitis/dandruff

• M. pachydermatis – only non-lipophilic species; transmitted by dogs

Clinical features:

• Discrete, serpentine, scaling macules (hyper- or hypopigmented)

• Spots enlarge and coalesce

• Common sites: chest, upper back, arms, abdomen

• Chronic, non-irritating

• More common in hot, humid, tropical climates

• Annual incidence: 5–8%

Complications in immunocompromised:

• Folliculitis

• Catheter-acquired fungemia (lipid therapy)

Diagnosis:

• Specimen: skin scrapings (or blood/catheter tips for fungemia)

• KOH + Parker Ink prep → "spaghetti and meatballs" appearance

  • Short, unbranched, nonpigmented hyphae + spherical yeast cells

• Wood's lamp: yellow-green fluorescence

• Culture (only for fungemia): SDA + olive oil overlay or Dixon's agar; incubate at 30°C for 5–7 days → cream to tan yeast-like colonies

• No serological tests available

Treatment:

• Selenium sulfide or zinc pyrithione (10–14 days)

• Topical imidazole with 50% propylene glycol (2x/day, 14 days)

• Relapse → oral itraconazole 200 mg/day for 5–7 days + prophylactic topical therapy

2. Tinea Nigra

Pathogen: Hortaea werneckii (dematiaceous fungus; previously Exophiala werneckii)

Clinical features:

• Dark brown to black, non-scaling macules on the palms (no inflammation)

• Solitary macule with sharply defined margins, spreads by expansion

• Darkest color at the advancing periphery

• May resemble melanoma or silver nitrate stain

• Prevalent in warm coastal areas; common in young women

• Endemic: Central/South America, Africa, Asia

Diagnosis:

• Specimen: skin scrapings (outer stratum corneum)

• KOH + Parker ink or calcofluor white or H&E

• Microscopy: pigmented (dematiaceous), septate hyphae + 2-celled yeast cells producing annelloconidia

• Brown color rules out dermatophytosis, candidiasis, and pityriasis versicolor

• Culture on SDA (+antibiotics): white-gray yeast-like → becomes velvety, olive to black

• No serology needed

Treatment:

• Whitfield's ointment (benzoic acid)

• Imidazole agent 2x/day for 3–4 weeks

• Keratolytic solutions (salicylic acid)

3. Black Piedra

Pathogen: Piedraia hortae

Clinical features:

• Hard, black nodules on the hair shaft (scalp, beard, mustache, pubic hair)

• Common in Africa, Asia, Latin America

• Spreads in families via shared combs/brushes

Diagnosis:

• Specimen: epilated hairs with hard black nodules

• KOH + Parker ink or calcofluor white

• Microscopy: black nodules contain ascostromata with asci (8 ascospores, tapering at both ends) + septate hyphae

• Culture on SDA: dark brown-black, slow-growing colonies (25°C, 2–3 weeks); may produce reddish-brown diffusible pigment; colony reverse is black

• Microscopic: dark septate hyphae + intercalary chlamydoconidium-like cells

Treatment:

• Shave or cut hair short

• Topical antifungal cream/shampoo

• Oral terbinafine 250 mg/day for 6 weeks

4. White Piedra

Pathogen: Trichosporon species (T. asahii, T. asteroides, T. inkin, T. ovoides, Cutaneotrichosporon cutaneum)

Clinical features:

• Soft, white to light brown nodules (1.0–1.5 mm) on hair shaft

• Affects axillary, pubic, beard, and scalp hairs

• No pathological changes to the hair

• Common in young adults

• T. asahii (75%) — causes opportunistic disseminated infections in leukemia, solid tumors, AIDS

• Natively resistant to echinocandins

Diagnosis:

• Specimen: epilated hairs with soft white nodules

• KOH + Parker ink or calcofluor white

• Microscopy: irregular soft nodules firmly adhering to hairs; yeast-like cells

• Culture: hair fragments on SDA → white to cream, smooth, wrinkled, velvety colonies with mycelial fringe

• Microscopy of culture: septate hyphae, pseudohyphae, arthroconidia, blastoconidia

Treatment:

• Shave or remove infected hairs

• Topical imidazole to prevent reinfection

• Oral terbinafine

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