[Ingrown nail: A new cause of chronic perionyxis]

Retronychia is the phenomenon of ingrown nail resulting in inflammation of the proximal subungual fold and is a newly described entity. Herein, we report a new case revealed through chronic proximal perionyxis.

A 52-year-old woman followed up for hypothyroidism, for which she was receiving treatment, consulted for pain in the lateral fold of the left big toe that had been ongoing for four months and for which glomic tumour was the suspected cause. Questioning revealed repeated microtrauma due to wearing of tight shoes and lack of growth of the toenail over the previous four months (in contrast with the contralateral toenail). Examination showed painful proximal perionyxis of the left big toe, with discharge from the subungual fold. Ultrasound examination of the subungual fold revealed effusion of fluid around the matrix, and this was confirmed by MRI. Surgical avulsion of the nail was carried out, and recovery was complete.

Retronychia is the result of a loss of continuity between the nail plate and the nail matrix, generally as a result of mechanical factors (distal trauma). However, unlike onychomadesis or Beau's lines, there is a disturbance of alignment between the two parts of the nail, which is normally maintained by the proximal subungual fold. This prevents newly formed nail from progressing towards the distal part of the plate, which itself is pushed into the nail bed and forced towards the proximal fold, causing inflammation of the latter structure. In our case, the pain recorded in the lateral fold was misleading, hence the ultimately unnecessary use of MRI to rule out the hypothesis of glomic tumour. Paronychia, discontinuation of nail growth and weeping through the subungual fold all argued in favour of a diagnosis of retronychia, which was confirmed by surgery. Surgical nail removal is the curative treatment for retronychia and results in complete cure without relapse or occurrence.

Retronychia should be suspected in the event of persistent proximal perionyxis, particularly in a setting of trauma with interrupted nail growth. Nail avulsion constitutes both a diagnostic and a therapeutic procedure.