Subungual exostosis
Dupuytren exostosis (original eponym); subungual osteocartilaginous exostosis
Subungual exostosis is a benign osteocartilaginous outgrowth of the distal phalanx that lifts the nail plate from below — most often on the great toe of an adolescent or young adult. It is a classic clinical mimic of subungual melanoma, verruca or pyogenic granuloma, and is frequently missed for months until plain radiography is requested. The combination of a firm, fixed subungual mass with elevation of the nail plate and a confirmatory bony exostosis on X-ray is diagnostic. Surgical excision is curative with low recurrence.
Clinical features
- Firm, fixed, often pink or skin-coloured subungual nodule lifting the nail plate.
- Onychogryphosis, onycholysis or partial nail loss; may bleed or ulcerate.
- Pain on pressure, particularly with footwear; precipitated by trauma in many cases.
- Distribution — distal phalanx of the great toe (~ 70%); other toes and fingers less common.
- Median age 10–25; both sexes; minor preceding trauma frequent.
Investigation
- Plain radiograph of the affected digit — AP and lateral — confirms a discrete bony outgrowth arising from the distal phalanx with a cartilaginous cap.
- MRI is occasionally required for atypical or recurrent lesions.
- Biopsy is rarely needed but excisional histology confirms benign trabecular bone with a fibrocartilaginous cap.
Differential
- Subungual melanoma — pigmented, longitudinal melanonychia, Hutchinson sign; mandatory biopsy if any pigment.
- Verruca vulgaris — softer, punctate haemorrhages, no bony attachment.
- Pyogenic granuloma — friable, red, bleeding, recent growth.
- Glomus tumour — exquisite point tenderness with cold exposure.
- Subungual SCC — chronic dystrophy, periungual change; biopsy.
- Osteochondroma — broader, typically away from nail unit, usually multiple.
Management
- Surgical excision under digital block — partial or complete nail-plate avulsion, excision of the exostosis at its base, with histology.
- Suturing of the nail bed if defect, replacement of the avulsed nail plate as a biological dressing.
- Recurrence rate < 10% with complete excision.
- Refer to plastic surgery, orthopaedic surgery or specialist podiatric surgery as appropriate.
References
- Dupuytren G. Original description of subungual exostosis. 1817.
- DaCambra MP, Gupta SK, Ferri-de-Barros F. Subungual exostosis of the toes — a systematic review. Clin Orthop Relat Res; 2014.
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