HYPONYCHIUM ABNORMALITIES Congenital Aberrant Hyponychium vs. Acquired Pterygium Inversum Unguis vs. Acquired Reversible Extended Hyponychium: a proposed classification based on origin, pathology and outcome

Background Pterygium Inversum Unguis (PIU) is a wing‐like extended hyponychium associated with the absence of the distal groove. Although a rare condition, it has been described with different names, confusing both the investigator and the reader. Objective We propose a new nomenclature based on tissue origin and pathology, to account for these conditions. 1) Congenital Aberrant Hyponychium 2) Acquired Pterygium Inversum Unguis 3) Acquired Reversible Extended Hyponychium. Main Observations We report a case of a 19‐year‐old male, with epidermal pigmentation abnormalities, who had painful fingertips of both index fingers and thumbs since he was 13. He therefore let his finger nails grow very long, minimizing painful contact with the hyponychium. Removal of the aberrant hyponychium revealed glomus bodies aggregates with increased nerve fibers. Subsequently after excision of the hyponychium, his pain was resolved. Summary Congenital, transient or permanent changes in the hyponychium should be named and classified according to tissue origin to avoid nomenclature confusion.