Subungual Exostosis of the Finger with Nail Plate Induction

Abstract

Subungual exostosis (SE) is a solitary, commonly sessile, bony growth firmly attached to the tuft of the underlying distal phalanx. It is a benign osteocartilaginous tumor arising underneath or beside the nail bed and may disrupt nail growth. Initially described in the hand by Hutchinson in 1857 [8], Dupuytren wrote about his experience with its manifestation in the foot a decade earlier [4]. The differential diagnosis of SE spans many possible nail, soft tissue, and bony pathologies. Onchomycosis, granuloma pyogenicum, epithelioma, verruca, keratoacanthoma [12], fibroma, glomus tumor [11], melanotic whitlow [3], osteochondroma [2], turret exostosis [13], juxtacortical chondroma, and myositis ossificans [1] have all been mentioned as potential diagnoses. The etiology and pathogenesis of SE is not clearly established. It is most commonly thought to reflect a fibrocartilaginous metaplasia from trauma or chronic infection [5, 9]. Although the latter may be a secondary consequence, as SE can elevate the nail causing exposure of the underlying soft tissue. However, others have alluded to genetic etiology [6], supranumery digits, cartilaginous rests, or a forme fruste of hereditary multiple exostoses [10]. SE is seen predominantly in females in a ratio of up to 2:1 [2, 5], though one series documented occurrence more often in males [8]. It occurs primarily in children and young adults in the second or third decades of life and more often affects the great toe, up to 77% of the time [9]. SE is best diagnosed on lateral radiographic view. It is usually seen as a bony projection on the dorsal or dorsomedial aspect of the distal phalanx capped with fibrous tissue. Early lesions may have insufficient bony formation to show up on X-rays [7]. No surrounding destructive changes are seen, supporting this as a benign diagnosis. SE is treated surgically. The nail plate may be removed, and excision is either through the nail bed [11] or via a midlateral incision [2]. Complete resection of the fibrocartilaginous cap is compulsory as local recurrence rates of 11% have been reported [9]. On histology, SE is composed of a mature trabecular pattern of a cancellous bone base with a proliferating fibrocartilaginous cap. The growth, which can reach more than 2 cm in diameter, is always benign. Our case report is the first description of aberrant induced nail plate growth with SE in the literature.