Description of Ringworm (Tinea Corporis)
Ringworm (tinea corporis) is a superficial fungal infection of the skin on the trunk and extremities caused by dermatophyte fungi, typically presenting as well-demarcated, circular or oval, erythematous, scaly patches or plaques with a raised, active border and central clearing. 1, 2
Clinical Presentation
The classic appearance includes:
- Annular (ring-shaped) lesions with sharply circumscribed borders
- Raised, advancing edge with central hypopigmentation or clearing
- Mild to moderate pruritus (itching) is common
- Scaly surface with erythema (redness)
- Lesions can be single or multiple, ranging from small patches to extensive plaques 2
Atypical Presentations
Recognizing atypical variants is crucial, as they can complicate diagnosis:
- Rupioid-like lesions (oyster-shell appearance) have been documented 3
- Prior use of topical corticosteroids or calcineurin inhibitors can mask typical features, making diagnosis difficult 2
- Presentation varies by skin tone—in darker skin (higher Fitzpatrick scale), hypopigmentation may be more prominent than erythema 1
Causative Organisms
Dermatophyte molds cause ringworm, with common species including:
- Trichophyton rubrum (most common)
- Trichophyton mentagrophytes
- Microsporum canis
- Rare species like Nannizzia incurvata can cause unusual presentations 3
Important Clinical Pitfalls
The differential diagnosis is broad and includes:
- Nummular eczema
- Pityriasis rosea
- Plaque psoriasis
- Tinea versicolor
- Granuloma annulare
- Discoid lupus erythematosus
Clinical diagnosis without laboratory confirmation is unreliable—other conditions frequently mimic tinea corporis 4. When in doubt, obtain diagnostic confirmation through potassium hydroxide (KOH) preparation or fungal culture, especially before initiating systemic therapy 2.
Emerging Concerns
Be aware of increasingly severe, antifungal-resistant dermatophyte strains:
- Trichophyton indotineae (terbinafine-resistant, spreading globally) 5
- Trichophyton mentagrophytes genotype VII (associated with severe infections) 5
- These emerging pathogens may require prolonged treatment and specialized diagnostic testing 4
Key Diagnostic Features
Dermoscopy can be a useful non-invasive tool to visualize characteristic features and aid diagnosis 2. The gold standard for confirmation remains fungal culture, particularly when the diagnosis is uncertain, lesions are extensive or resistant to treatment, or the patient is immunocompromised 2.