Background: Microsporum gypseum is a geophilic dermatophyte that colonises keratinous substances in the soil. Fur-bearing animals carry this dermatophyte but are rarely infected. Human infection can be acquired from the soil, carrier or infected animals, and rarely other humans. M gypseum is an uncommon cause of cutaneous infection in humans and typically manifests as tinea corporis, tinea barbae, and tinea capitis. Onychomycosis is rarely caused by M gypseum.
Case summary: We present a case of a 32-year-old white man who presented with a red scaly rash and nail dystrophy after adopting a pet rat 10 years prior to presentation. A fungal culture of a nail clipping grew out M gypseum, and the patient was treated with terbinafine daily for 6 weeks for dystrophic onychomycosis and tinea corporis. After the 6 weeks of treatment, the erythema at the proximal nail fold and distal finger had improved but still persisted. An additional 6 weeks of terbinafine daily completely resolved the clinical manifestations of onychomycosis.
Conclusion: The increase in incidence of M gypseum onychomycosis over the past 2 decades is thought to be due to phylogenetic evolution of the dermatophyte from soil saprophyte to a human parasite. Increasing domestication of mammals is also thought to contribute to increasing incidence. Treatment consists of an extended course of terbinafine or itraconazole.
Keywords: Microsporum gypseum; onychomycosis; tinea corporis.