Sir,

Retronychia is a relatively rare and little-known condition. The term retronychia comes from retro, meaning backwards, and onychia, meaning nail [1]. It frequently affects young females and mainly affects the big toe unilaterally, yet may also be bilateral or affect the fingers [2]. It is thought to be a chronic proximal paronychia resulting from the nail embedding in the proximal nail fold with a break in the continuity between the matrix and the nail plate, so that when the nail grows, the new plate pushes the old one upward and forward and embeds it in the posterior fold, causing inflammation of the latter [1–4]. It is probably due to mechanical factors including acute anteroposterior pressure applied against the free edge of the nail or by chronic repetitive microtraumas [1,2,5]. The diagnosis should be made in the presence of the clinical triad of chronic paronychia, oozing through the proximal fold, and cessation of nail growth [2,3]. Other signs may be found, such as yellowish discoloration of the shelf, Beau’s lines, superficial leukonychia, subungual hematoma, and Beau’s lines [2,3]. Chronic paronychia is often mistaken for a candidal or bacterial infection, resulting in delayed diagnosis [3]. Proper management includes the elimination of risk factors such as microtrauma and total nail avulsion, which confirms the diagnosis by revealing several generations of overlapping nails and represents the curative treatment of retronychia, as illustrated by our cases. It allows normal nail regrowth without relapse or recurrence, with excellent functional and aesthetic results [1,3]. The recognition of this underdiagnosed disease entity helps to avoid local complications, prolonged pain and discomfort, and unnecessary antibiotic treatment [2,4]. Herein, we report two new cases.

Case one was a 25-year-old female who presented two months before her consultation with a painful inflammation of the proximal fold of the right hallux with cessation of nail growth. Questioning revealed a notion of repeated microtrauma caused by wearing tight shoes. An examination revealed a painful peronyxis of the right big toe with xantonychia (Fig. 1a). The diagnosis of retronychia was suspected and the avulsion of the nail, with evidence of two superimposed nail generations confirming the diagnosis. The patient had no recurrence after one year of follow-up (Fig. 1b).

Figure 1: (a) Peronyxis of the right big toe with xantonychia. (b) One year after avulsion.

Case two was a 27-year-old female who consulted for a painful periungual inflammation of the left hallux that appeared following repeated micro-trauma that dated back six months. The nail did not grow back anymore. A clinical examination revealed a painful paronychia of the left big toe with serosal discharge through the proximal fold and a distal xantonychia (Fig. 2a). Complete avulsion of the nail plate revealed three superimposed nails (Figs. 3a and 3b). The evolution was marked by normal nail regrowth. The current follow-up is three years without a recurrence (Fig. 2b).

	Figure 2: (a) Paronychia of the left big toe with distal xantonychia. (b) Three years after avulsion (patient was tanned).
	Figure 3: (a) Avulsion of the nail. (b) Three superimposed nails.

Consent

REFERENCES

1. Chiheb S, Richert B, Belyamani S, Benchikhi H. [Ingrown nail:A new cause of chronic perionyxis]. Ann Dermatol Venereol. 2010;137:645-7.

2. Poveda-Montoyo I, Vergara-de Caso E, Romero-Pérez D, Betlloch-Mas I. Retronychia a little-known cause of paronychia:A report of two cases in adolescent patients. Pediatr Dermatol. 2018;35:144-6.

3. Reigneau M, Pouaha J, Créa T, Truchetet F. Rétronychie:un ongle peut en cacher un autr. Ann Dermatol Venerol. 2012;139:B224.

4. Robledo A, Godoy E, Manrique E, Manchado P. Retronychia:An underdiagnosed disease. Dermatol Online J. 2017;23:16.

5. Agharbi FZ, Chiheb S. Paronychie chronique re?ve?lant une re?tronychie. PAMJ Clinical Medicine. 2020;3:59.