Pathogenesis and Risk Factors
Dermatophyte fungi are classified as keratinophiles. This means they require keratin for survival, which they break down using the enzyme keratinase. However, the depth of infection is strictly limited: the fungi never penetrate deeper than the epidermal basement membrane.
Several factors contribute to the development of the disease:
- External (exogenous): hyperhidrosis, skin maceration, microtrauma.
- Internal (endogenous): reduced overall host resistance, endocrine disorders.
- Iatrogenic: prolonged antibiotic therapy disrupting normal microflora.
Clinical Manifestations and Localization
Clinically, dermatomycoses are usually classified by anatomical site of infection (topographic classification):
- Tinea corporis (trunk, extremities).
- Tinea facialis and Tinea barbae (face and beard area).
- Tinea capitis (scalp).
- Tinea manus and Tinea pedis (hands and feet).
- Tinea cruris (groin area).
- Tinea unguium (nail involvement, or onychomycosis).
Symptoms depend on the structures involved:
- Glabrous skin: severe pruritus, scaling, fissuring, as well as vesicles and pustules. Inflammation can range from prominent to barely noticeable.
- Hair: hair shafts break, leading to patches of alopecia (hair loss).
- Nails (onychomycosis): the nail plate loses transparency, changes color, thickens, and becomes brittle. The primary culprits here are most frequently Trichophyton rubrum and Trichophyton interdigitale.
Laboratory Diagnostics
The diagnosis is confirmed through microbiological studies.
Microscopic Method (Rapid Test) Skin scrapings, hair fragments, or nail clippings are collected for analysis. The specimen is cleared in a 10–15% KOH solution (for 10–15 minutes) to dissolve obstructing keratin. Microscopic examination reveals mycelial threads, blastospores, and conidia (macro- and microconidia). The arrangement of spores on the hair helps suggest the causative agent:
- In Trichophyton, arthroconidia lie in parallel chains (Ectothrix — outside the hair shaft, Endothrix — inside).
- In Microsporum, spores form a mosaic pattern on the outside of the hair shaft.
- In favus, fungal elements and characteristic gas bubbles are visible inside the hair.
Culture Method Inoculation of material onto media (e.g., Sabouraud dextrose agar). Incubation at 25 °C takes 1 to 3 weeks. This method is essential for precise species identification based on colony morphology.
Additional Methods: serology (ELISA, complement fixation test for antibodies), skin allergy testing, and animal inoculation (bioassay).
Treatment and Prevention
Therapy is selected based on the site of infection:
- Scalp: systemic agents are indicated (fluconazole, terbinafine, griseofulvin, itraconazole).
- Onychomycosis: a combination of topical agents and systemic antimycotics (ketoconazole, terbinafine, fluconazole, griseofulvin).
- Feet: topical creams or ointments are usually sufficient (e.g., clotrimazole, ketoconazole, terbinafine), but systemic antimycotics and antihistamines are added in severe cases.
Prevention includes personal hygiene measures (such as using individual footwear only), early case detection, screening of contacts, and mandatory disinfection of the focus of infection.