Subungual Exostosis

Key Points
Condition results in a growth of bone from the tip of the toe or finger below the nail.
Cause is unknown, but there are several possibilities including constant bone irritation, previous trauma or long infections.
Condition more prevalent in adult women.

Subungual exostosis is a growth of bone from the tip of the toe or finger. This happens below the nail, hence the term subungual. It is a benign tumor grown from the bone and cartilage. A firm nub develops below the nail bed and, as it grows upwards, the nail plate separates from the bed often causing pain. The lesion usually grows slowly over weeks to months. The cause is unknown. Constant irritation to the bone has been proposed as a possible factor. Previous trauma and long infections may contribute. There are two inherited conditions that can develop subungual exostosis: multiple exostoses syndrome and multiple exostoses-mental retardation syndrome.

The most common site for the lesion is on the big toe, usually on the inside. Less commonly subungual exostosis can occur on the fingers, most commonly on the index and middle fingers. Subungual exostosis may occur at any age but half of the reported cases tend to occur by 20 years of age. Women are more commonly affected.

Differential Diagnosis (other conditions with similar appearance)
Subungual verruca
Pyogenic granuloma
Osteochondroma
Amelanotic Melanoma
Glomus tumor

Diagnosis
Key Points
X-rays are important to confirm the origin.
Biopsies are rarely required.

X-rays of the lesion are important to confirm the bony origin. Biopsies are rarely required.

Treatment
Key Points
Surgical removal is the treatment of choice, with bone scraping to prevent future recurrence.

Surgical removal of the lesion is the treatment of choice. The tumor is completely removed and the underlying bone is scraped clean to prevent future recurrence.