Subungual exostosis

Dermatology consultation was sought for a man in his early 30s presenting with gradually progressive slightly painful nodular growth under the medial border of the left big toenail which he first noticed 8 months ago. His big toes had previously looked normal, and there had been no prior history of injury or infection affecting this nail. The nodular growth had a smooth, hyperkeratotic surface, a well-defined contour, and was firm with mild tenderness. The left toenail plate was elevated as a result of its extension beyond the free edge of the nail’s medial border [Figure 1a]. Radiograph of the foot revealed an osseous protrusion projecting from the dorsomedial aspect of the terminal phalanx of the first toe [Figure 1b]. There was no evidence of calcification of the soft tissues and destructive changes. This was considered to be consistent with the subungual exostosis. After getting the exostosis surgically removed, the patient experienced satisfactory symptom relief and no local recurrence.

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Figure 1:

(a) Nodular growth with a smooth, hyperkeratotic surface, a well-defined contour under the medial border of the left big toenail (b) radiograph of the foot shows osseous protrusion projecting from the dorsomedial aspect of the terminal phalanx of the first toe.

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Subungual exostosis may be defined as a solitary and benign tumor of bone occurring on the distal phalanx beneath the nail. It was first described by Dupuytren in 1847. Subungual exostosis is most commonly seen in the great toe although other toes and fingers can also be involved. The clinical features include subungually located solid mass along with swelling of the digit, onycholysis, paronychia, elevation and subsequent detachment of nail plate, erosion, and ulceration of surrounding soft tissue. The radiograph usually shows pedunculated radiopaque mass arising from the dorsal surface of the distal phalanx. Excision and curettage of the subungual exostosis are the treatment of choice. Conditions such as ingrown toe nail, subungual verruca, pyogenic granuloma, keratoacanthoma, carcinoma of nail bed, subungual epidermoid inclusion, and periungual fibroma should be differentiated from subungual exostosis.^[1] A typical case of subungual exostosis is frequently misdiagnosed and mistreated by clinicians. Awareness among the clinicians regarding this uncommon entity will help in early diagnosis and prompt treatment of this condition.