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Answer in short
a. Clinical Diagnosis: Dermatophytosis (Ringworm / Tinea corporis) - fungal infection presenting as circular patches with elevated red margins and clear center (central clearing), recurring over 6 months.
b. Specimens to Collect: Skin scrapings from the active border/edge of the lesion (not the center).
c. Method of Collection:
- Clean the lesion with 70% alcohol and let it dry
- Using a sterile blunt scalpel or the edge of a glass slide, scrape the active advancing edge (elevated margin) of the lesion
- Collect scales into a folded black paper or sterile container
- Do not scrape the clear central area (less fungal elements there)
d. Laboratory Tests:
| Test | Detail |
|---|---|
| Direct Microscopy (KOH mount) | 10-20% KOH added to skin scrapings; look for branching septate hyphae |
| Culture | Inoculate on Sabouraud's Dextrose Agar (SDA) with cycloheximide + chloramphenicol; incubate at 25-28°C for 2-4 weeks |
| Lactophenol Cotton Blue (LPCB) stain | To identify fungal morphology (macroconidia/microconidia) of dermatophytes like Trichophyton, Microsporum, or Epidermophyton |
| Wood's Lamp | Greenish fluorescence seen in Microsporum infections |
| Dermatophyte Test Medium (DTM) | Color change from yellow to red indicates dermatophyte |
Likely causative agent: Trichophyton rubrum (most common cause of Tinea corporis).
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