Tinea Capitis by Microsporum canis in an Elderly Female with Extensive Dermatophyte Infection

Tinea capitis is a type of dermatophyte infection primarily affecting children. We report a case of an elderly woman with well-controlled diabetes mellitus presenting with a six-month history of erythema with yellow crusts on her scalp and extensive erythematous patches with scales on the body skin. She adopted a stray cat before the disease onset. Dermoscopic findings and manifestation under the Wood's lamp favoured the diagnosis of tinea capitis. Further microscopic examinations of her scalp, including direct KOH and fluorescence stain examination, fungal culture and polymerase chain reaction sequencing identification confirmed the diagnosis of tinea capitis caused by Microsporum canis. Treatment with oral terbinafine was effective. Adult tinea capitis is often misdiagnosed due to its rarity and atypical presentation. However, in some regions, the incidence of tinea capitis in immunocompetent adults is rising which requires the awareness of clinicians. A thorough history (including the animal contacting history), physical examination and further mycological examinations are required for diagnosis. Trichophyton violaceum is the most common dermatophyte species in most regions while adult tinea capitis caused by Microsporum canis is less common. Terbinafine, griseofulvin and itroconazole have been reported to be effective drugs for the treatment of tinea capitis, and terbinafine can be considered as systemic treatment in elderly patients with comorbidities to reduce the drug-drug interaction.