Superficial Mycoses

Intro to Superficial Mycoses - Surface Fungal Foes

• Fungal infections limited to the outermost layers of skin, hair, and nails (stratum corneum, hair shaft, nail plate).
• Caused by dermatophytes and non-dermatophyte molds (e.g., Malassezia, Piedraia, Trichosporon).
• Primarily cosmetic; minimal inflammation or tissue destruction.
• Transmission: direct contact with infected individuals, animals, or fomites.
• Diagnosis: clinical appearance, KOH microscopy, Wood's lamp.

⭐ Superficial mycoses generally do not elicit a significant host immune response because they are confined to the non-living, keratinized layers of skin and hair.

Pityriasis Versicolor - Skin's Color Chaos

• Causative Agent: Malassezia furfur (lipophilic yeast, normal skin flora).
• Mechanism: Malassezia produces dicarboxylic acids (e.g., azelaic acid) that inhibit tyrosinase, leading to altered pigmentation.
• Clinical Features:
  • Well-demarcated, hypo- or hyperpigmented, or erythematous macules and patches.
  • Fine, branny scales (furfuraceous scaling), often elicited by scraping (Besnier's sign).
  • Common sites: Trunk, upper arms, neck, abdomen (sebaceous gland-rich areas).
  • Usually asymptomatic; mild pruritus may occur.
• Predisposing Factors: Warm, humid climate; oily skin; hyperhidrosis; immunosuppression; malnutrition.
• Diagnosis:
  • KOH mount (10-20%): Characteristic "spaghetti and meatballs" appearance (short, curved septate hyphae and clusters of yeast cells).
  • Wood's lamp: Yellow-green to golden-yellow fluorescence (due to pteridine pigments).
• Treatment:
  • Topical: Selenium sulfide (2.5%), ketoconazole shampoo/cream, ciclopirox, terbinafine solution.
  • Systemic (for extensive/recurrent cases): Itraconazole, fluconazole.

⭐ The characteristic 'spaghetti and meatballs' appearance (hyphae and yeast cells) of Malassezia furfur on KOH mount is pathognomonic for Pityriasis versicolor.

Tinea Nigra & Piedras - Dark Stains & Hair Stones

Tinea Nigra

• Causative Agent: Hortaea werneckii (dematiaceous fungus).
• Clinical: Asymptomatic, solitary, flat, dark brown/black macule. Non-inflammatory, non-scaly.
• Site: Palms (classic), soles.
• Diagnosis: KOH mount (pigmented hyphae, budding cells).
• Treatment: Topical antifungals (azoles, terbinafine), Whitfield's ointment.

⭐ Tinea nigra, caused by Hortaea werneckii, presents as a non-inflammatory, non-scaly, dark brown to black macule, often on the palms, and must be differentiated from melanocytic nevi or melanoma.

Piedras (Hair Stones)

• Fungal infection forming nodules on hair shafts.

Lab Dx & Rx Summary - Fungal ID & Aid

⭐ Direct microscopic examination of clinical specimens (skin scrapings, plucked hairs) using a KOH wet mount is the most rapid and cost-effective method for diagnosing superficial mycoses.

Key investigations include KOH mount, culture (SDA; Malassezia needs lipid), and Wood's lamp. Summary:

High‑Yield Points - ⚡ Biggest Takeaways

• Malassezia furfur causes Pityriasis versicolor; KOH shows "spaghetti and meatballs" appearance.
• Pityriasis versicolor lesions exhibit yellow-green fluorescence under Wood's lamp.
• Hortaea werneckii is the causative agent of Tinea nigra, presenting as dark macules on palms/soles.
• Piedraia hortae causes Black piedra, characterized by hard, dark nodules on hair shafts.
• Trichosporon species are responsible for White piedra, forming soft, pale nodules on hair.
• Superficial mycoses are non-invasive, strictly limited to the stratum corneum or outermost hair/nail layers.
• Treatment typically involves topical antifungal agents like azoles or selenium sulfide for efficacy and safety.