The cause of subungual exostosis is unclear; however, it is thought to occur as a reaction to:
– constant irritation
– previous trauma
– chronic infection
– or due to some inherited conditions such as multiple exostoses syndrome.
– Exostosis grows gradually over weeks and months.
– It presents as a hard painful swelling under or beside the toenail, usually on its inner side.
– As it grows it presses against the nail, causing pain, which may be confined to the nail fold.
– With further growth, it separates the nail from the nail bed and erodes the overlying skin (making it prone to infections).
Subungual exostosis is often misdiagnosed for other conditions such as an ingrowing toenail or a malignant tumour.
Clinical examination should be supported by an X-ray to confirm its bony origin. There may be a history of previous trauma. A biopsy may also be a helpful diagnostic tool, but is rarely required.
As an exostosis continues to grow, damaging the surrounding tissues, the best treatment option is to remove the bony projection altogether via surgery.
The procedure is done under local anesthesia. The exostosis is removed, along with the attached nail bed. The surface of the underlying bone is scraped to ensure complete removal of the exostosis and prevent its recurrence in the future. Even then, it is reported to recur in 10% of cases.
Sometimes, a significant area of the nail bed has to be excised along with the lesion; a plastic reconstruction may be required later on.