Onychomatricoma
Onycomatricoma; nail-matrix fibroepithelioma
Onychomatricoma is a rare but characteristic benign fibroepithelial tumour of the nail matrix that produces a distinctive triad of thickened yellow nail plate, longitudinal cavitations on the under-surface of the nail and splinter haemorrhages. The nail plate is often hyperkeratotic and curved, with a band of yellow or white discolouration. Diagnosis is confirmed by clinical examination, dermoscopy of the free edge of the nail, ultrasound or MRI, and definitive histology after nail-matrix biopsy or excision. Complete surgical excision is curative.
Clinical features
- Thickened, hyperkeratotic, often yellow or pale-brown nail plate.
- Longitudinal cavitations / "honey-comb" channels on the under-surface of the nail plate — pathognomonic.
- Splinter haemorrhages within the nail plate.
- Curving of the nail plate (transverse and longitudinal over-curvature).
- Distribution — fingers commoner than toes; usually a single digit.
- Median age 40–60; both sexes; slow growth over years.
Investigation
- Dermoscopy of the free edge — multiple parallel longitudinal channels are highly characteristic.
- Ultrasound — hypoechoic nail-matrix mass.
- MRI — well-circumscribed nail-matrix lesion with fibrous and epithelial components; useful for surgical planning.
- Definitive diagnosis by nail-matrix biopsy or excisional histology — fibroepithelial tumour with digitations of fibrous stroma covered by matrix epithelium, mirroring the cavitations seen clinically.
Differential
- Onychomycosis — KOH / culture / nail clipping; commoner and less structured.
- Subungual SCC — chronic dystrophy, biopsy mandatory.
- Subungual melanoma — pigmented; longitudinal melanonychia.
- Glomus tumour — exquisite cold-induced point tenderness.
- Verruca, subungual exostosis, fibroma — see related monographs.
Management
- Complete surgical excision of the nail-matrix tumour — partial or complete nail-plate avulsion, excision of the matrix lesion, reconstruction.
- Performed under digital block by clinicians experienced in nail-unit surgery.
- Recurrence after complete excision is uncommon.
- Pathological confirmation is essential to exclude SCC or melanoma.
References
- Baran R, Kint A. Onychomatrixoma — filamentous tufted tumour of the matrix of a funnel-shaped nail. Br J Dermatol; 1992.
- Perrin C et al. Onychomatricoma — clinical and histopathological findings in 12 cases. J Am Acad Dermatol; 1998.
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