Background: Pterygium inversum unguis is a rare abnormality of the nail bed that remains adherent to the ventral surface of the nail plate, resulting in a subungual extension of the hyponychium and obliteration of the distal groove.
Objective: The aim of our article is to illustrate the cases of pterygium inversum unguis that we observed in the last 20 years and to discuss them according to a broad review of the literature.
Results: Nineteen new cases of pterygium inversum unguis have been observed: one congenital idiopathic form, five acquired idiopathic forms, and 13 secondary forms.
Conclusion: Our study and the review of the literature demonstrate that the most common forms of pterygium inversum unguis are the acquired secondary ones. They are generally related to systemic connective tissue diseases and, in particular, to progressive systemic sclerosis and systemic lupus erythematosus.