Eruptive inflammatory tinea corporis: a case report highlighting the role of molecular testing on formalin-fixed tissue in confirming the causative species.

BACKGROUND: Dermatophytosis is a fungal skin infection most commonly caused by members of the genera Trichophyton, Microsporum, and Epidermophyton, though there are 7 genera currently described including Arthroderma, Nannizzia, Paraphyton and Lophophyton. These filamentous fungi survive in the stratum corneum of the hair, skin, or nails of their host by metabolizing keratin. Dermatophyte skin infections can be acquired from direct contact with the skin of infected individuals or animals, fomite transmission, contaminated soil, or autoinfection from other infected body sites. These fungal skin infections are commonly known as "ringworm" due to their classic clinical presentation as an annular, pruritic, scaling patch or plaque that contains an area of central clearing and an expanding and raised active border.

CASE DESCRIPTION: The case of a 22-year-old female with blistering rash involving the neck, abdomen, arms, and lower extremities is presented. Her clinical presentation, along with a similar rash in her fiancé and a concurrent scaling rash in her dog, led to a broad differential diagnosis. Histopathology revealed superficial fungal elements, and molecular testing on paraffin-embedded tissue confirmed Microsporum canis as the causative organism. The patient and household contacts were successfully treated with systemic and topical antifungals, with no recurrence over 6 months.

CONCLUSIONS: This case report highlights an uncommon presentation of tinea corporis caused by a zoophilic dermatophyte and underscores the importance of maintaining clinical suspicion even in atypical cases. Molecular identification methods such as broad-range fungal polymerase chain reaction (PCR) can be valuable tools in establishing the diagnosis when conventional diagnostics are unavailable or inconclusive.