Characteristic Lesion Features of Tinea Corporis
Tinea corporis characteristically presents as well-demarcated, sharply circumscribed, oval or circular, mildly erythematous, scaly patches or plaques with a raised, active leading edge 1.
Primary Morphologic Features
The classic presentation includes the following key features:
- Annular (ring-shaped) configuration with central clearing and an advancing scaly border that is more prominent than the center 1
- Erythematous base with variable intensity, typically mild to moderate 1
- Scaling that is most pronounced at the periphery of the lesion 2, 1
- Raised leading edge representing the active border of fungal invasion 1
- Mild pruritus is commonly present, though not always 1
Diagnostic Confirmation
While the clinical appearance is often sufficient for diagnosis, confirmation can be obtained through:
- Potassium hydroxide (KOH) microscopy of skin scrapings from the active border, which typically shows hyphae and/or arthroconidia 3
- Specimens should be collected using a blunt scalpel to remove skin scale from the advancing edge 3
- Fungal culture on Sabouraud agar with cycloheximide incubated for at least 2 weeks serves as the gold standard when diagnosis is uncertain 3, 1
Clinical Variants and Atypical Presentations
Important variations to recognize include:
- Bullous tinea corporis (tinea corporis bullosa anularis) can present with bullous borders in addition to the typical erythematous and scaling features 4
- Multiple overlapping lesions may develop, creating polycyclic or serpentine patterns 5
- Prior use of topical corticosteroids or calcineurin inhibitors can significantly alter the typical appearance, making diagnosis more challenging 1
Common Diagnostic Pitfalls
- Do not rely solely on clinical appearance if the patient has used topical steroids, as this can mask the characteristic features and create "tinea incognito" 1
- Ensure specimens are taken from the active border, not the center, as the fungal elements are concentrated at the advancing edge 3
- Consider dermoscopy as a useful non-invasive diagnostic adjunct when the clinical picture is unclear 1