Cutaneous P. lilacinum Hyalohyphomycosis Infection: Atypical Histomorphology in an Immunocompetent Patient

Hyalohyphomycosis is an opportunistic fungal infection caused by a variety of environmental, hyaline (i.e., non-pigmented) molds and is often associated with skin and/or systemic manifestations in immuncompromised individuals. Herein, we describe a case of a 73-year-old immunocompetent individual who recently immigrated from Cambodia with cutaneous hyalohyphomycosis caused by Purpureocillium lilacinum. The patient presented with pruritic, pink-to-violaceous, linear plaques and papules on the right dorsal forearm that had been present for 2-3 years. Biopsy showed superficial granulomatous dermatitis without appreciable fungal forms on H&E staining; special stains revealed non-pigmented, fungal elements, prompting tissue culture, from which a filamentous fungus exhibiting pale mauve colonies was recovered. Phenotypic and morphologic features were consistent with Paecilyomyces spp., and the identity was confirmed as Purpureocillium lilacinum (formerly Paecilomyces lilacinus) by reference lab testing. The patient was successfully treated with oral terbinafine, with lesions resolving by 12 weeks post-treatment. This study examines the clinical features of hyalohyphomycosis and summarizes the relevant literature, including treatment guidelines and antifungal susceptibility patterns. It also emphasizes the importance of histopathology and microbiologic culture in the diagnosis of cutaneous fungal infections.