Primary cutaneous non-pigmented mycotic cyst contained in an epidermal inclusion cyst: Case report and review of the literature

Primary cutaneous mycotic cysts are uncommon dermal or subcutaneous fungal lesions. The most commonly implicated organisms are species within a heterogeneous group of pigmented fungi called dematiaceous fungi. Mycotic cysts usually present as solitary lesions and can be caused by traumatic introduction of fungal elements by foreign bodies or present as a cutaneous manifestation of systemic fungal infections, especially in immunocompromised patients. We present a case of a 63-year-old immunocompetent male who developed a non-erythematous solitary nodule after doing yardwork. Histopathologically, a benign-appearing epidermal inclusion cyst was apparent containing a splinter with keratinous granular debris and no indication of inflammatory host reaction. However, abundant non-pigmented hyphae were visualized after a periodic acid-Schiff stain was performed. This case offers an interesting histopathological view of a non-pigmented mycotic cyst contained within an epidermal inclusion cyst with a true epithelial lining. It also raises the question of whether mycotic cysts caused by non-pigmented fungi are rare or simply under-diagnosed because of their deceptively benign initial appearance. Even in the absence of an inflammatory or granulomatous host response, we recommend investigating for fungal elements in lesions where a splinter or other foreign body material is present in order to avoid misdiagnosis.