A case of kerion celsi caused by Trichophyton tonsurans with dermatophytid reaction mimicking a drug eruption and endothrix infection confirmed in pathological tissue.

We report a case of kerion celsi caused by Trichophyton tonsurans in a teenage male judo athlete, presenting with a lesion in the occipital region. Following the initiation of systemic antifungal therapy, the patient developed a dermatophytid reaction, necessitating differentiation from a drug eruption. Direct microscopy of the affected area confirmed the presence of fungal elements, and histopathological examination revealed endothrix invasion, supporting the continuation of treatment. A drug-induced lymphocyte stimulation test for terbinafine, conducted post-treatment, was negative. This case highlights the importance of distinguishing dermatophytid reactions from drug eruptions to ensure uninterrupted antifungal therapy.