Tinea Incognito

Tinea incognito is a dermatophyte infection whose appearance has been altered by topical (or systemic) corticosteroids or calcineurin inhibitors, leading to a modified, less scaly and often more extensive eruption. Misdiagnosis as eczema is the commonest cause.

• Causative organisms: Trichophyton rubrum, T. mentagrophytes and others.
• Risk factors: previous mistaken diagnosis, over the counter steroid creams, immunosuppression, diabetes, crowded living, shared items.

Itchy or burning erythematous plaques that lack the classic scaly raised border, with papules, pustules, follicular involvement and sometimes nodules (Majocchi granuloma) after steroid use.

• Rapid relapse after stopping steroids; spreading and more extensive disease.
• Differential diagnosis: eczema, psoriasis, seborrhoeic dermatitis, contact dermatitis, rosacea, lupus erythematosus, granuloma annulare, cutaneous candidiasis, impetigo, folliculitis, mycosis fungoides, lichen planus.
• Complications: deep folliculitis and kerion, Majocchi granuloma, steroid atrophy and striae, widespread infection, persistent disease, transmission to contacts.

Clinical suspicion, confirmed by direct microscopy with KOH, fungal culture and sometimes PCR.

• Scrape from the margin, hair pluck for follicular lesions, biopsy with PAS stain for nodular disease.
• Glucose, HIV test where indicated.

Stop the corticosteroid, taper if potent or long term, and treat the fungus.

• Supportive: emollient to soothe rebound inflammation, loose cotton clothing, personal towels, treat footwear, keep skin dry, inspect household contacts and pets.
• Pharmacological: terbinafine 250 mg daily for 2 to 4 weeks (children by weight: under 20 kg 62.5 mg, 20 to 40 kg 125 mg, over 40 kg 250 mg daily); alternatives itraconazole 100 mg daily for 2 to 4 weeks, or fluconazole 150 to 200 mg weekly for 4 weeks. Topical terbinafine 1 percent or clotrimazole 1 percent twice daily for 2 weeks beyond clinical clearance. After stopping a potent steroid, a mild steroid (hydrocortisone 1 percent) once daily for a few days may ease the rebound.
• Procedures: none; incise and drain abscess-like areas only if required.
• Special groups: pregnancy, topical clotrimazole only and avoid oral azoles and terbinafine; liver disease, avoid oral terbinafine and itraconazole or check liver tests; HIV, longer course; children, weight based terbinafine or griseofulvin 10 mg/kg daily.
• Red flags: nodules and pustules (Majocchi granuloma), extensive spread, immunosuppression, failure of response in 4 weeks, jaundice or abnormal liver tests on terbinafine.
• Follow-up: review at 2 and 4 weeks; baseline and repeat liver tests for courses beyond 4 weeks; counsel against using steroid creams without confirmed diagnosis.