Dermatophytoses

Introduction & Etiology - Fungal Foes

• Dermatophytoses: Superficial fungal infections of keratinized tissues (skin, hair, nails).
• Etiologic agents: Dermatophytes (keratinophilic fungi).
• Key Genera (📌 TME):
  • Trichophyton: Affects skin, hair, nails.
  • Microsporum: Affects skin, hair.
  • Epidermophyton: Affects skin, nails.
• Ecological Classification:
  • Anthropophilic: Human-to-human (e.g., T. rubrum).
  • Zoophilic: Animal-to-human (e.g., M. canis).
  • Geophilic: Soil-to-human (e.g., M. gypseum).
• Pathogenesis: Keratinase enzymes digest keratin, facilitating invasion.

⭐ Trichophyton rubrum is the most common dermatophyte globally, frequently causing chronic infections like tinea pedis and tinea cruris.

Clinical Manifestations - Ringworm Roundup

• General: Annular, erythematous, scaling plaques; active, raised border; central clearing. Pruritus common.
• Tinea Corporis (Body): Classic ringworm on trunk, limbs.
  • 
• Tinea Cruris (Groin): "Jock itch". Erythematous patches on inner thighs, inguinal folds; scrotum spared.
• Tinea Pedis (Feet): "Athlete's foot".
  • Types: Interdigital (most common, maceration), Moccasin (diffuse scaling), Vesiculobullous (vesicles/bullae).
• Tinea Manuum (Hands): Often unilateral scaling; "Two feet, one hand" syndrome.
• Tinea Capitis (Scalp): Alopecia, scaling, broken hairs.
  • Patterns: Ectothrix, Endothrix.
  • Inflammatory: Kerion (boggy mass).
  • Chronic: Favus (scutula; yellowish, cup-shaped crusts).

  ⭐ Wood's lamp: Microsporum spp. fluoresce blue-green; Trichophyton spp. usually do not.

• Tinea Barbae (Beard): Pustular folliculitis in beard area.
• Tinea Unguium (Onychomycosis): Nail discoloration, thickening, subungual debris. Distal Lateral Subungual Onychomycosis (DLSO) common.
• Tinea Faciei (Face): Annular lesions on non-bearded face; often photosensitive distribution if topical steroids misused (tinea incognito).

Diagnostic Methods - Spotting Spores

• KOH Mount (10-20%): Primary test. Skin/nail/hair scrapings. Dissolves keratin, reveals septate hyphae & arthrospores.

  ⭐ Calcofluor white stain under fluorescent microscope provides rapid and brilliant visualization of fungal elements.

• Fungal Culture: Gold standard for species ID. Sabouraud Dextrose Agar (SDA) ± antibiotics. Dermatophyte Test Medium (DTM) shows color change (yellow → red).
• Wood's Lamp (UV 365nm): Greenish fluorescence with some Microsporum spp. (e.g., M. canis). Not all fluoresce.
• Biopsy: PAS/GMS stains for atypical/deep infections.

Management Strategies - Kicking Keratin-lovers

• Goal: Eradicate infection, prevent recurrence.
• General: Hygiene, dry skin, loose cotton clothing.

• Tinea Capitis: Systemic therapy essential (Griseofulvin/Terbinafine). Add antifungal shampoo (Ketoconazole/Selenium sulfide).
• Onychomycosis: Systemic preferred (Terbinafine/Itraconazole).
• ⚠️ Avoid irrational steroid combinations; risk of Tinea Incognito.

⭐ Terbinafine is fungicidal via squalene epoxidase inhibition; Azoles are generally fungistatic via 14-α-demethylase inhibition, targeting lanosterol demethylation to ergosterol.

Special Aspects - Tricky Tineas

• Tinea Incognito: Steroid-modified, ↓inflammation, atypical presentation.
• Majocchi's Granuloma: Deep follicular invasion (T. rubrum), often legs, immunocompromised.
• Tinea Imbricata: Concentric scaly rings ("Tokelau"), T. concentricum.
• Favus (Tinea Capitis): T. schoenleinii, scutula (yellow crusts), scarring alopecia.

⭐ Majocchi's granuloma is a deep fungal folliculitis, commonly on legs of women (shaving) or in immunocompromised patients.

High‑Yield Points - ⚡ Biggest Takeaways

• Dermatophytes (Trichophyton, Microsporum, Epidermophyton) are keratinophilic fungi infecting skin, hair, and nails.
• Tinea corporis (ringworm) typically presents as annular lesions with central clearing and an active, erythematous border.
• Diagnosis is confirmed by KOH mount of skin scrapings showing septate hyphae; Wood's lamp helps identify some Microsporum species (e.g., M. canis fluoresces green).
• Tinea capitis often requires systemic antifungal therapy (e.g., griseofulvin, terbinafine), especially for endothrix infections.
• Onychomycosis (tinea unguium) is challenging to treat, usually necessitating prolonged oral antifungals like terbinafine or itraconazole.
• Treatment involves topical antifungals (azoles, allylamines) for localized infections, and oral agents for extensive disease, hair/nail involvement, or failed topical therapy.
• An Id reaction (dermatophytid) is a sterile, allergic hypersensitivity rash at a distant site from the primary fungal infection, not representing spread of infection.