Epidermal panfolliculoma: A report of 2 cases

There are a variety of known lesions displaying differentiation toward various portions of the hair follicle. However, there is no established term given to an intraepidermal entity showing differentiation toward both upper and lower portions of the follicle. We report 2 cases of a histologically distinct variant of panfolliculoma that, unlike the traditionally described panfolliculoma, is located intraepidermally. The lesions were taken from the medial thigh of an 81-year-old man and the lateral thigh of a 61-year-old woman, clinically suspected to be an inflamed seborrheic keratosis and a squamous cell carcinoma, respectively. Each case appeared as a demarcated plaque-like lesion with mild epidermal hyperplasia and prominent differentiation toward the upper and lower segments of the hair follicle. The specific histologic features included focal differentiation toward the infundibulum and isthmus (infundibular cystic structures and pilar epithelium), inner root sheath (trichohyalin granules), the matrix/hair shaft (matrical cells, ghost cells and refractile keratinization), and follicular germ/papilla (papillary mesenchymal bodies). This varied histology is similar to that of the previously described panfolliculoma, differing in that it emanates largely from the epidermis rather than being predominantly dermally located. We propose the term "epidermal panfolliculoma" for these lesions.