Exostosis masquerading as a subungual wart.

Sir,

Subungual exostosis is a benign bone tumor found on the distal phalanx of the digit beneath or adjacent to nail. These lesions are different from osteocartilaginous lesions occurring in other parts of skeleton. This relatively uncommon tumor was first described by Dupuytren in 1847. The lesion is more commonly found in great toe (80%), but can also be seen in other toes. These lesions are often misdiagnosed as nail bed diseases due to the clinical similarities and hence they have to be evaluated in terms of their clinical, radiological, and histopathologic features.[1]

We present a 23-year-old patient with complaints of having pain and discharge underneath the great toe nail. It was initially misdiagnosed and treated by a dermatologist as refractory wart. With development of discharge, the patient consulted general surgeon, who treated it as a case of paronychia.

Examination revealed a swelling of about 1 × 1 cm arising from the nail bed on the medial side and lifting up the nail [Figure 1]. Radiological investigations revealed a bony outgrowth arising from the tuft of the distal phalanx [Figure 2].

Figure 1

Lesion elevating the nail plate

Figure 2

Bony outgrowth from tuft of distal phalanx

The patient was treated with surgical excision [Figure 3]. Histopathologic findings showed a bony mass consisting of mature lamellar trabeculae. The cartilaginous cap showed mature chondrocytes. The mass was surrounded by fibrosis and covered with keratin layer [Figure 4]. The findings were in favor of exostosis.

Figure 3

Surgical approach

Figure 4

Histopathology

Unlike the conventional exostoses, these lesions neither arise adjacent to epiphyseal growth plate which is basal in distal phalanx, nor are they found in association with multiple hereditary exostoses.[2] Exact cause for these tumors is unknown. Trauma may be the precipitating factor. Subungual exostoses may be the result of metaplasia of fibrocartilaginous tuft of phalanx due to chronic irritation with repeated trauma.[2] These lesions develop during adolescence and are more common in females. They present as solitary lesion, most often on the large toe. They can also be seen on the other digits. A striking finding is the preference for the inner border of the terminal phalanx of the large toe.[3]

Initially they start as small firm nodules underneath the free edge of nail, and as the exostosis expands, intensity of the pain increases and nail plate is pushed up and finally gets separated. It gets covered by a mass of fibrous tissue and may get infected. This is the stage at which a dermatologist is likely to see the patient. It has to be differentiated from subungual verruca, granuloma pyogenicum, glomus tumor, carcinoma of the nail bed, melanoma, keratoacanthoma, subungual epidermoid inclusions, and enchondroma. Radiographs show bony projection on dorsomedial aspect of distal phalanx.[4] Surgical excision is the treatment of choice and complete resection reduces the recurrence rate.[1]

Histopathology shows mature trabecular pattern base which differentiates it from chondrosarcoma as the proliferating fibrocartilaginous cap may show multinucleated chondrocytes, pleomorphic nuclei, and a prominent cellular structure.[5]

To conclude, subungual exostosis is a benign fibrocartilaginous lesion of the distal phalanx that is infrequently seen in clinical practice. It should be included in the differential diagnosis of entities presenting with finger tip pathology.