Tinea Corporis (Ringworm)

Causative Organisms and Pathogenesis

Tinea corporis is caused by three main dermatophyte genera: Trichophyton, Microsporum and Epidermophyton. Based on where the infection comes from, they fall into three ecological groups:

• Anthropophilic (human-to-human): Most commonly Trichophyton rubrum and Trichophyton interdigitale. These spread between people through direct contact or shared personal items. The resulting lesions tend to be chronic with mild to moderate inflammation, but they relapse easily and often coexist with athlete's foot (tinea pedis) or fungal nail infection (tinea unguium).
• Zoophilic (animal-to-human): Most commonly Microsporum canis (from dogs and cats) and Trichophyton mentagrophytes (from rabbits and rodents). These infections tend to flare acutely with intense inflammation and deep pustules along the border.
• Geophilic (soil-derived): Microsporum gypseum (from soil). It causes an acute inflammatory reaction and is less common than the other two groups.

How the Ring-Shaped (Annular) Pattern Forms: Once fungal spores (arthroconidia) attach to smooth skin, they secrete keratinases, proteinases and esterases that dissolve keratin and let them penetrate the stratum corneum. The hyphae then grow outward evenly in all directions, prompting the local immune system to release inflammatory cytokines (IL-1, TNF-alpha). Inflammation is strongest at the outermost margin, producing a raised, red "active border" with papules and vesicles. In the center, as the body clears the fungus, the skin gradually heals and fades (central clearing).

Tinea Incognito: A serious complication that occurs when patients apply combination creams containing potent corticosteroids on their own (such as "7-color" cream, Dibetalic or Gentrisone). The steroid suppresses local inflammation, so the classic ring-shaped active border disappears completely. Meanwhile, the fungus spreads freely into hair follicles and the dermis, producing widespread, ill-defined red patches with mixed superficial and deep pustules that can completely mislead the initial clinical diagnosis.

Clinical Features and Differential Diagnosis

Tinea corporis typically appears as coin-shaped or ring-shaped red patches, sharply demarcated from the surrounding normal skin. The edge is raised, with tiny vesicles, red papules and fine scale, while the center is paler and tends to heal or show light peeling. Itching ranges from moderate to severe and worsens with sweating or hot, humid weather.

Clinical Differential Diagnosis Table

Standard Diagnostic Workup at Haute-Derma

• Dermoscopy of Smooth Skin: Direct examination of the advancing edge:
  • Scale clinging to the edge of the lesion, with its free margin pointing toward the center (inward-facing scale).
  • Dotted (punctate) vessels clustered along the raised border.
  • In tinea incognito, follicular papules and pustules and tortuous dilated vessels.
• Direct KOH 10–20% Microscopy with Calcofluor White Fluorescent Staining:
  • Using a dedicated blunt blade, the technician gently scrapes scale from the advancing edge, where active hyphae are most concentrated.
  • The scale is soaked in 20% KOH to dissolve the keratin, then stained with Calcofluor White (or Parker ink).
  • Under the fluorescence microscope, spores and septate branching hyphae glow a vivid blue, confirming the diagnosis with high accuracy.
• Fungal Culture and Antifungal Susceptibility Testing: Indicated for widespread disease, failure of standard treatment, or suspected resistance to azoles or allylamines. Specimens are cultured on Sabouraud dextrose agar (SDA) for 2–3 weeks.

Comprehensive Treatment Protocol at Haute-Derma

Topical Antifungal Therapy — First Choice for Localized Disease: For small lesions covering < 10% of body surface area without tinea incognito.

• Allylamines (first choice, strongly fungicidal): terbinafine 1% or naftifine 1% cream, applied 1–2 times daily.
• Azoles (broad-spectrum, fungistatic): ketoconazole 2%, clotrimazole 1%, miconazole 2% or sertaconazole 2% cream, applied twice daily.
• Hydroxypyridones: ciclopirox olamine 1%, applied twice daily.

Haute-Derma application rules:

• Apply at least 2–3 cm beyond the visible border to reach hyphae spreading silently under the stratum corneum.
• Keep applying for 1–2 weeks AFTER the redness and itching have completely cleared to eliminate any remaining spores.

Systemic Antifungal Therapy — Extended Indications: Used for extensive disease (> 10% of body surface area), failure of topical therapy, immunocompromised patients, or tinea incognito extending into hair follicles.

• Oral terbinafine: 250 mg once daily after a meal for 2–4 weeks.
• Oral itraconazole: 100–200 mg once daily, taken right after a main meal containing fat, for 1–2 weeks.

Managing Tinea Incognito and Secondary Infection:

• Stop all corticosteroid-containing creams immediately.
• If there are signs of bacterial superinfection (ruptured pustules with yellow oozing and crusting): warm compresses with KMnO4 1:10,000 or chlorhexidine 0.12%, plus an oral antibiotic (such as cephalexin) for 5–7 days.
• Start oral antifungal therapy right away (terbinafine 250 mg/day) together with a plain antifungal cream.

Behavior and Home Hygiene:

• Treat any other fungal infections on the body at the same time (such as athlete's foot or nail fungus) to remove sources of self-reinfection (auto-inoculation).
• Disinfect clothing, underwear and towels by boiling (> 60°C) for 15 minutes or by hot washing and tumble drying.
• Check household pets (dogs, cats) as a possible source and take them to a veterinarian if they have patches of hair loss or scaling.