Subungual exostosis

Subungual exostoses are osteochondromas. They occur mainly under the medial nail folds of the great toes, although they can appear on the lesser toes.

They present with a complaint of pain in the toe, sometimes localised to the nail fold. Sometimes the swelling itself may cause pressure on the shoe. Some have a history of trauma or previous nailbed surgery (which may have been for an "ingrowing toenail' that was, in fact, the exostosis).

Examination shows a firm swelling under the nail, usually in the medial nail fold. It is usually covered with epidermis, but may be raw or granulating.

The main differential diagnosis is ingrowing toenail, with a nailbed tumour such as melanoma, squamous carcinoma or glomus tumour as a much rarer possibility.

The lesion normally continues to grow so is best removed when diagnosed. This can be done under digital block anaesthesia as a day case. Sometimes the nail fold can be elevated and preserved, but usually it cannot be separated from the lesion and must be sacrificed. Even with careful excision of the whole lesion, the recurrence rate averages about 10%.

Subungual exostosis