Diagnosis: Tinea Corporis (Ringworm)
A circular, red, papular rash with central exfoliation is most consistent with tinea corporis (ringworm), which should be confirmed with potassium hydroxide (KOH) examination of skin scrapings from the active border before initiating antifungal therapy. 1
Key Diagnostic Features
The clinical presentation described is pathognomonic for dermatophyte infection:
- Annular configuration: Circular lesions with raised, erythematous borders and central clearing/scaling are characteristic of tinea corporis 1
- Centrifugal growth pattern: The rash expands outward from the center, leaving scale or exfoliation in the middle as the active infection moves peripherally 1
- Pruritic nature: These lesions are typically intensely itchy 1
Diagnostic Confirmation
- KOH preparation is essential: Obtain skin scrapings from the active, raised border (not the center) and perform KOH wet-mount examination to visualize fungal hyphae 2, 1
- Clinical diagnosis alone is insufficient: While the appearance is suggestive, confirmation prevents misdiagnosis and inappropriate treatment 2
Differential Diagnosis to Exclude
Several conditions can mimic this presentation and must be considered:
- Nummular eczema: Presents with coin-shaped erythematous plaques (1-10cm diameter) but typically has more diffuse scaling rather than central clearing, and KOH will be negative 2, 3, 1
- Psoriasis (annular variant): Shows sharply demarcated erythematous plaques with silvery scale, but lacks the advancing border with central clearing pattern 1
- Pityriasis rosea: Multiple lesions with raised scaly borders, but typically follows a "Christmas tree" distribution on the trunk 1
- Granuloma annulare: Annular lesions but non-scaly and typically asymptomatic 1
Treatment Approach
Once tinea corporis is confirmed by KOH examination:
- Topical antifungals are first-line: Apply terbinafine cream, clotrimazole, or miconazole twice daily to affected areas and 2cm beyond the visible border 1
- Treatment duration: Continue for 2-4 weeks, or at least 1 week after clinical resolution to prevent recurrence 1
- Systemic therapy indications: Consider oral antifungals (terbinafine, itraconazole, or fluconazole) for extensive involvement, immunocompromised patients, or failure of topical therapy 1
Common Pitfalls to Avoid
- Do not treat empirically without KOH confirmation: Misdiagnosis can lead to inappropriate corticosteroid use, which will worsen fungal infections 2, 1
- Avoid topical corticosteroids as monotherapy: While they may temporarily reduce inflammation, they facilitate fungal spread and can cause tinea incognito 4
- Do not sample from the center: The active infection is at the advancing border; central areas contain only scale and dead organisms 1
When to Refer
- Dermatology consultation indicated for: Recalcitrant cases not responding to 4 weeks of appropriate antifungal therapy, uncertain diagnosis despite KOH testing, or need for skin biopsy 5
- Consider patch testing: If the condition persists despite negative KOH and failed antifungal treatment, nummular eczema with contact allergy becomes more likely 2