Tinea (Dermatophyte) Skin Infection: Diagnosis and Treatment
Diagnosis
The diagnosis of tinea corporis should never be made on clinical appearance alone and requires mycological confirmation through potassium hydroxide (KOH) preparation microscopy and/or fungal culture before initiating treatment. 1, 2, 3
Clinical Presentation to Look For:
- Well-demarcated, sharply circumscribed, oval or circular erythematous patch or plaque with a raised, scaly leading edge 4
- Mild pruritus is common 4
- Central clearing with active border progression 5
- May have associated tinea pedis (foot infection) in up to one-third of cases 6
Diagnostic Testing:
- Collect skin scrapings from the active border of the lesion using a scalpel, scraping outward from the edge where fungal elements are most concentrated 1, 2
- Submit adequate material for both KOH microscopy (immediate results) and fungal culture on Sabouraud's glucose agar (definitive species identification) 1, 7
- If first specimen is negative but clinical suspicion remains high, repeat sampling is mandatory 2
Common Diagnostic Pitfall:
The most common cause of treatment failure is incorrect diagnosis based solely on clinical grounds without laboratory confirmation, as only 50% of suspected fungal skin conditions are actually fungal 7, 3
First-Line Treatment
For localized tinea corporis, topical antifungal therapy applied for 2-4 weeks is first-line treatment. 1, 5
Topical Antifungal Options:
- Clotrimazole cream applied twice daily for 2-4 weeks 1
- Miconazole cream applied twice daily for 2-4 weeks 1
- Ketoconazole 2% cream applied once daily for 2 weeks (FDA-approved regimen) 8
- Allylamine agents (e.g., terbinafine) for 1-2 weeks 5
Continue treatment for at least one week after clinical clearing to reduce recurrence risk. 8, 5
When to Use Oral Antifungal Therapy
Oral antifungal therapy is indicated when the infection is extensive, resistant to topical treatment, involves hair follicles, or the patient is immunocompromised. 1, 3
Oral Treatment Options:
- Terbinafine 250 mg daily for 1-2 weeks is particularly effective against Trichophyton tonsurans 1, 3
- Itraconazole 100 mg daily for 15 days has an 87% mycological cure rate (superior to griseofulvin's 57%) 1
Treatment Selection Based on Organism:
- Terbinafine appears superior for Trichophyton tonsurans infections 1
- Itraconazole is effective but has important drug interactions with warfarin, certain antihistamines, antipsychotics, midazolam, digoxin, and simvastatin 1
- Avoid griseofulvin as first-line—it requires longer treatment duration and has lower cure rates 1
Prevention and Recurrence Management
Implement these measures to prevent recurrence and transmission: 1
- Avoid skin-to-skin contact with infected individuals 1
- Do not share towels, clothing, or personal items 1
- Cover lesions during treatment 1
- Clean contaminated combs, brushes, and fomites with disinfectant or 2% sodium hypochlorite solution 1
- Screen and treat all family members if infection is caused by anthropophilic species (e.g., T. tonsurans), as over 50% may be affected 1
Treatment Monitoring
Follow-up should include both clinical and mycological assessment to confirm mycological cure, not just clinical improvement. 1
- Repeat mycology sampling until mycological clearance is documented 1
- If treatment fails, extend treatment duration or consider switching to oral therapy 1
- Baseline liver function tests are recommended before initiating terbinafine or itraconazole, especially with pre-existing hepatic abnormalities 1
Critical Caveats
- Never use combination antifungal-corticosteroid preparations as first-line therapy—they can cause skin atrophy, mask the infection, and promote antifungal resistance 5, 3
- Inadequate specimen collection from superficial areas rather than the active border contributes to false negatives 7, 2
- Prior use of topical corticosteroids or calcineurin inhibitors can alter clinical appearance and make diagnosis difficult 4