How should I diagnose and manage a 24-year-old male with a one‑year history of an asymmetric, well‑demarcated, large circular plaque with raised scaly erythematous borders and central clearing on the abdomen and buttock region that has not responded to oral and topical antifungal therapy?

Reconsider the Diagnosis: This is Likely NOT Tinea Corporis

Given the complete failure to respond to both oral and topical antifungal therapy over one year, you must urgently reconsider the diagnosis—this presentation strongly suggests an alternative diagnosis such as psoriasis, granuloma annulare, subacute cutaneous lupus erythematosus, or another inflammatory dermatosis rather than a fungal infection.

Immediate Diagnostic Steps

The clinical description of large, well-demarcated circular plaques with raised scaly erythematous borders and central clearing on the abdomen and buttocks that have persisted for one year without response to antifungals demands immediate diagnostic confirmation:

1. Obtain Definitive Mycological Confirmation

• Perform scalpel scraping of the active border for potassium hydroxide (KOH) examination and fungal culture 1
• If KOH and culture are negative, tinea corporis is effectively ruled out
• True tinea corporis should respond to appropriate antifungal therapy within 2-4 weeks

2. Perform Skin Biopsy

Since antifungal treatment has failed completely, a 4mm punch biopsy from the active border is essential to establish the correct diagnosis. The differential diagnosis includes:

• Psoriasis: Look for well-demarcated erythematous plaques with silvery scale. The buttock region is a common site for psoriasis 2. Histology would show regular acanthosis, parakeratosis, and neutrophils in the stratum corneum
• Granuloma annulare: Presents with annular plaques and can mimic tinea 3, 4
• Subacute cutaneous lupus erythematosus: Can present with annular erythematous plaques 5
• Superficial basal cell carcinoma or intraepidermal carcinoma: Both can present as well-defined erythematous plaques 6
• Porokeratosis: Characterized by hyperkeratotic annular plaques with raised margins 7

Management Algorithm Based on Diagnosis

If Mycology is Negative (Most Likely Scenario):

For Psoriasis (Most Probable Given Distribution and Chronicity):

Start with topical corticosteroids combined with vitamin D analogs 2, 8:

• Initial therapy: Apply a potent topical corticosteroid (Class 2-3) twice daily to the plaques for 2-4 weeks
• Combination approach: Add calcipotriene (vitamin D analog) once daily, or use combination calcipotriene/betamethasone dipropionate once daily 2
• Maintenance: Transition to weekend-only corticosteroid use while maintaining vitamin D analog 5 days per week to prevent atrophy 2
• Alternative topicals: If corticosteroids are contraindicated or ineffective, use coal tar (0.5-10% crude coal tar in petroleum jelly) or dithranol (0.1-0.25% increasing to 10%) 8

Important caveats:

• Limit potent corticosteroids to <100g per month 8
• Require regular clinical review with no unsupervised repeat prescriptions 8
• Buttock/intertriginous areas require careful monitoring for atrophy 2

For Granuloma Annulare:

• Many cases are self-limited
• Potent topical corticosteroids under occlusion
• Consider intralesional corticosteroid injection for localized lesions
• Screen for systemic sarcoidosis if sarcoidal features are present on histology 4

For Subacute Cutaneous Lupus:

• Refer to rheumatology
• Systemic workup for lupus
• Topical corticosteroids and sun protection
• May require systemic immunosuppression

If Mycology is Positive (Unlikely Given Treatment Failure):

This would suggest either:

1. Inadequate dosing or duration of previous antifungals
2. Non-dermatophyte infection (Candida or mold) requiring different therapy 9
3. Reinfection from contaminated clothing or environment

For confirmed dermatophyte infection resistant to standard therapy:

• Terbinafine 250mg daily for 4-6 weeks (not the 2-4 weeks used for tinea capitis) 1
• If Microsporum species: Griseofulvin 1g daily for 6-8 weeks 1
• Consider itraconazole 200mg daily for 4 weeks as second-line 1

Critical Pitfalls to Avoid

1. Do not continue empiric antifungal therapy without mycological confirmation—you risk missing serious diagnoses including malignancy 6
2. Do not assume all annular lesions are fungal—the differential is extensive 3
3. Do not use low-potency corticosteroids for thick plaques—they provide minimal benefit for established psoriatic plaques 2
4. Do not ignore the one-year duration—chronic lesions unresponsive to appropriate therapy mandate biopsy

Next Steps Summary

1. Stop all antifungal therapy immediately
2. Obtain KOH prep and fungal culture from active border
3. Perform 4mm punch biopsy from the raised border
4. While awaiting results, if psoriasis is clinically suspected, initiate potent topical corticosteroid + vitamin D analog combination
5. Adjust therapy based on histopathology results
6. Ensure close follow-up within 2-4 weeks to assess response

The complete lack of response to antifungal therapy over one year is the key clinical clue that this is not a fungal infection and requires immediate diagnostic reassessment.