Clinical Presentation and Localization
Rubrophytosis has characteristic clinical manifestations that are important to recognize. The pathological process involves specific structures of the human body.
Common sites of infection:
- Skin of the trunk.
- Skin of the upper and lower extremities.
- Nail plates (onychomycosis).
- Vellus hair (unlike other dermatophytes, which more frequently infect terminal hair).
Typical lesions form on the affected areas of the skin. They appear as small pink macules with well-defined borders. Small vesicles and drying crusts can be found on the surface and edges of these lesions.
Microscopic Findings
Microscopy is crucial for the laboratory diagnosis of dermatophytosis. The morphology of Trichophyton rubrum differs significantly depending on whether clinical material from a patient is examined or the fungus is grown on nutrient agar.
In clinical specimens (skin scrapings): Examination of scrapings reveals threads of septate mycelium that branch actively. Arthrospores—elements formed by the breakdown of hyphae into individual fragments—are seen significantly less often.
In pure culture: When Trichophyton rubrum is grown in vitro, the mycelium retains its structure (thin, branched, septate hyphae), but characteristic spore-bearing structures appear:
- Microconidia: Small, pyriform (pear-shaped) or oval spores. They typically form clusters rather than appearing singly.
- Macroconidia: Large, elongated, pencil-shaped spores measuring up to 6 × 50 µm.
- Chlamydoconidia: These thick-walled resting spores are absent in young colonies and begin to form only as the fungal culture ages.