Onychomatricoma in the Light of the Microanatomy of the Normal Nail Unit

The study investigated onychomatricoma (OM), a rare benign nail tumor, to determine its differentiation patterns and relationship to hair follicle structures. Researchers examined 6 OM cases using keratin antibodies and found that hair keratins were expressed in a pattern similar to the normal nail matrix. The study identified new histopathological and immunohistochemical features of OM, categorizing its presentation into two main patterns: lobulated or foliated, and "glove-finger" mono- or multidigitate. The findings suggested that OM can replicate the entire nail unit with differentiation toward the nail bed and isthmus, and it was concluded that OM is not a variant of other pilar tumors. The study proposed the concept of an epithelial onychogenic tumor with onychogenic mesenchyme to better understand OM's nature, while maintaining the term OM due to its established usage.