An 8-year-old, otherwise healthy boy presented with a 4-month history of a growing mass under the nail of his right fifth toe, painful on palpation, which caused onycholysis. The patient denied recent trauma or occurrence of similar lesions in the past. Family history was unremarkable. X-Ray showed a dorsomedial exostosis, of approximately 4×3 mm, on the right fifth toe.

Dupuytren’s subungual exostosis (SE) is a rare heterotopic ossification that commonly involves the first toe or, more rarely, other toes or fingers. It usually presents with a solitary, fixed, painful, sometimes ulcerated or infected dorsomedial mass on the distal phalanx of toes or fingers, associated with elevation and dystrophy of the nail plate. The majority of patients are younger than 18 years. Triggers may be trauma or infections. The diagnosis is confirmed by radiography or histology.

Fig. 1 Dupuytren’s subungual exostosis; (a) mass under the nail of fifth toe causing onycholysis, and (b) radiograph showing dorsomedial exostosis (arrow).

Differential diagnosis includes viral warts, pyogenic granuloma and osteochondroma. Papillomavirus periungual warts are firm, keratotic papules which are located around the nail. They can be painful and cause onycholysis and hyperkeratosis. Pyogenic granuloma, an acquired benign vascular tumor, appears as a rapidly growing erythematous, soft, friable nodule with erosive surface and tendency to bleed under pressure, commonly located on fingers and toes but also in the head and neck region and oral mucosa. Osteochondroma is clinically similar to Dupuytren’s SE but radiographically and histologically different – unlike the latter, in the majority of the cases, osteochondroma has continuity with the underlying bone and is covered by hyaline cartilage.

Surgical treatment should aim to preserve the nail plate; nevertheless, an incomplete excision may lead to recurrence.