A 13-year-old boy presented with a ‘growth’ beneath the nail of the right great toe (Fig. 1). The lesion was painful and had been present for the preceding 6 months. The nodule was tender, bony-hard in consistency, and measured 20 x 15 mm in diameter. The nail plate showed onycholysis. A radiograph revealed a calcified projection on the dorso-lateral part of the distal phalanx, continuous with the underlying bone (Fig. 2). Based on the clinical presentation and radiological features, a diagnosis of subungual exostosis was made.

Fig. 1 Subungual nodule with onycholysis.

Fig. 2 Radiograph showing calcified projection on the distal phalanx of the great toe (white arrows).

Subungual exostosis is a relatively rare, acquired, benign osteocartilaginous tumor occurring mainly in children and young adults. They are found beneath the distal edge of the nail, most commonly of the great toe. However, other toes or, occasionally, a finger may be involved. The first manifestation of this tumor is a painful, small, pink or flesh-colored, hard, exophytic growth that projects beyond the inner free edge of the nail. The overlying nail becomes brittle and may be lifted or become detached. The surface of the lesion may become hyperkeratotic. The exact pathogenesis of exostosis remains elusive. However, it probably reflects a reactive metaplasia resulting from micro-trauma. It should be differentiated from granuloma pyogenicum (sessile, friable, vascular nodule, which bleeds easily on touch), verruca vulgaris (verrucous nodule, devoid of skin markings; multiple bleeding points are seen on pairing of the lesion), glomus tumor (skin-colored or blue-red nodule; on palpation: extremely tender with radiating pain), and squamous cell carcinoma (usually found at the sulcus of the nail; presents as a growth under the distal lateral edge of the nail; usually a long term history of several years is present).

However, the bony consistency of the nodule would usually suggest the correct diagnosis. Plain radiography can generally confirm it, exhibiting an exostotic tumor arising from the dorsal aspect of the distal phalanx as in the present case. Complete excision or curettage is the mainstay of treatment of this condition.