GD12 Tinea indotineae complicating and potentially propagated by psoriasis

Abstract

A 33-year-old Indian man presented in May 2023 with a 4-year history of a widespread scaly rash, clinically diagnosed as severe psoriasis. Methotrexate was ineffective and narrowband ultraviolet B phototherapy only briefly efficacious. He re-presented in September 2024 with widespread indurated, sparsely scaly plaques involving the trunk and genitalia (Psoriasis Area and Severity Index 23.5). Adalimumab and topical corticosteroids were commenced in November 2024. However, worsening pruritus prompted a skin biopsy. The punch biopsy indicated superficial fungal infection. Adalimumab was stopped and oral itraconazole 100 mg once daily commenced. Skin scrapings were sent to mycology. Fungal culture revealed Trichophyton indotineae resistant to terbinafine and sensitive to itraconazole. Mycology advised oral syrup itraconazole 200 mg twice daily and weaning off topical steroids. Ketoconazole 2.0% shampoo was introduced following a national multidisciplinary team (MDT) meeting. Mildly affected family members responded to the same regimen within 4 weeks. Clinical improvement was very slow despite 4 months of itraconazole with optimal trough levels, and several skin scrapings remained positive. In March 2025, the patient’s clinical presentation evolved, and a skin biopsy demonstrated a psoriasiform appearance. Mycology scrapings were microscopically positive but culture negative. MDT discussion in May 2025 prompted cessation of oral itraconazole, commencement of risankizumab and ongoing topical ketoconazole. Near complete resolution was seen by August 2025 (Psoriasis Area and Severity Index reduction from > 10 to 1.5). Our case highlights the need for clinical vigilance alongside serial skin scrapings, biopsies, photographs and MDT discussion. Family members were treated quickly to reduce the risk of reinfection. Trichophyton indotineae infection presents with widespread pruritic plaques, easily confused with chronic plaque psoriasis. Our case demonstrates both conditions overlapping and supports the hypothesis that psoriasis may provide a permissive host environment for T. indotineae. Diagnosis and sensitivity testing can take weeks and terbinafine resistance is common (approximately 60% of isolates). Protracted treatment is required and MDT review with mycology expertise invaluable.