Questioning the Terminology of “Retronychia Inversa”

The phenomenon described by Tordjman and coworkers under the denomination “retronychia inversa” [1] seems to be a simple form of onycholysis due to the obstacle represented by an old retained nail plate (NP), which acts as foreign body—a recognized [2], often overlooked cause of onycholysis. This is anatomically evident from the picture (Mendeley figure S1 of ref. [1], available at https://doi.org/10.17632/42c5kkvzxh.1) provided by the authors themselves to outline the results of their clinical observations (9 cases out of 12, with “total/severe onycholysis”; data not available as to the remaining 3 [1]), where a normal, proximal-to-distal growth of the new NP is impaired by the presence of the old retained one, which prevents the ventral attachment of the new one to the nail bed. Indeed, this phenomenon is suitably labeled “severe onycholysis” by the authors themselves in the legend of their picture. The best available and comprehensive definition of onycholysis is the following one: the separation of the NP from its bed starting from the free edge [3], without specifying the actual situation of the free edge with regard to the extremity of the finger/toe at the start of the process. Indeed, it is sometimes overlooked that, albeit quite less commonly, onycholysis can also develop proximally, usually as “a consequence of onychomadesis or tumors in the distant nail matrix” [4] or in the proximal part of the nail bed. Here the role of the “tumor” (in the literal sense of a “bulk” or a “bump”) is evidently played by the old retained, adherent NP, which the new one tends to “step over” dorsally, with a resulting onycholytic growth from the very proximal beginning. This possibly adds a curious, unusual case to the list of reactions to endogenous foreign bodies, but always within the spectrum of recognized patterns (to wit, in our case, simple onycholysis), without the need of introducing new nosological entities. Accordingly, the choice of the terminology proposed by Tordjman et al. [1] should be reconsidered. Owing to the fact that there are no clues to a proximally aberrant, then distally reverted effective retronychial growth, the authors could have made this choice to point out the inverse spatial relationship (“a layering pattern opposite to classical retronychia” [1]) between the retained and the newly growing NPs rather than a literal reversal of nail growth. However, this would imply that the term “retronychia” could be ambiguously applied to two different, only vaguely related clinicomorphological phenomena (only one thing in common: the retained old NP, so typical of genuine retronychia [5]). Should be this the case, in my humble opinion the term chosen by the authors would become cause of terminological confusion, would introduce an unnecessary complication, and should consequently be avoided. The author has nothing to report. The author declares no conflicts of interest. Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.