Tinea (Ringworm) Infections
Dermatophyte fungi cause tinea infections, which characteristically present as ring-shaped rashes with central clearing and an advancing, raised, scaly border. 1
Clinical Presentation
Tinea infections produce the classic "ringworm" appearance - erythematous lesions that spread centrifugally with central clearing, creating the distinctive ring pattern. 1, 2 The key distinguishing features include:
- Scaling and erythema at the peripheral border, which differentiates these fungal infections from other conditions like acanthosis nigricans 3
- Raised, advancing edges with active inflammation at the margins 2
- Pruritus is commonly present, unlike many non-fungal mimics 3
- Distribution can be asymmetric and may affect any skin surface, though specific anatomical patterns define different tinea subtypes 3
Common Tinea Subtypes
The specific anatomical location determines the clinical terminology:
- Tinea corporis affects the body/trunk and presents as the classic ringworm pattern 2, 4, 5
- Tinea cruris ("jock itch") involves the groin area 2, 5
- Tinea pedis affects the feet and toes 4
- Tinea capitis involves the scalp, primarily in prepubescent children 4
Diagnostic Confirmation
Skin scraping with KOH (potassium hydroxide) preparation provides definitive diagnosis and should be performed when clinical suspicion exists. 3 The optimal technique involves:
- Collect scales from the active border/edge of the ring where fungal elements are most abundant 6
- Fungal culture on selective media can identify the specific dermatophyte species, though this is not always necessary for treatment decisions 6
- Direct microscopy has up to 50% false-negative rate, so negative results don't exclude the diagnosis if clinical suspicion is high 6
Treatment Approach
Topical antifungal therapy is first-line for localized cutaneous fungal infections. 3 The evidence supports several effective options:
- Terbinafine demonstrates superior efficacy with clinical cure rates 4.5 times higher than placebo (NNT = 3) 5
- Naftifine 1% achieves mycological cure rates 2.4 times higher than placebo (NNT = 3) 5
- Azole antifungals (clotrimazole, miconazole) are effective alternatives with mycological cure rates 2.9 times higher than placebo (NNT = 2) 5
- Treatment duration typically ranges from 2-4 weeks, though some newer agents allow shorter courses 5
Systemic antifungals (oral terbinafine, itraconazole, or fluconazole) are necessary for extensive, resistant, or severe infections. 3, 4
Critical Pitfall
Avoid topical steroid-antifungal combination products despite their higher short-term clinical cure rates, as current clinical guidelines do not recommend them due to concerns about steroid-related complications and potential for relapse. 5 While some studies showed improved clinical appearance at end of treatment, the quality of evidence was very low and mycological cure rates were equivalent to antifungals alone. 5