Exostosis

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 Editor: Luc Thomas

 Author(s): Amélie Boespflug, Luc Thomas
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Subungual exostosis (SE) is an isolated acquired slow-growing subungual benign osteo-chondral outgrowth of the dorsal side of the distal phalanx of toes and fingers that is considered by some authors to be a variant of an osteochondroma [1]. In rare cases this outgrowth can be peri-ungual[2].


Subungual exostosis is uncommon even though it is probably underreported[2]. It commonly affects young adults of both genders and is mostly localized on the first right hallux[2]. Reactive metaplasia is believed to be caused by either an acute significant trauma or to minor repeated chronic trauma, and chronic infection [2].


Clinically it appears like an asymptomatic or painful subungual or peri-ungual nodule that uplifts the nail and causes nail dystrophy and onycholysis[2]. Due to its unspecific clinical presentation, accurate diagnosis is often delayed with an average time to diagnosis of 15 months[3].


Dermoscopically, vascular ectasia is the most frequent finding, followed by hyperkeratosis, onycholysis and ulceration. Subungual hyperkeratosis presents itself dermoscopically like a well delimited yellow spot that becomes more visible when pressure is applied by using the dermoscope[4].

Subungual Exostosis.jpg Subungual Exostosis 2.jpg

Differential diagnosis include : subungual warts[5], squamous cell carcinoma, amelanotic subungual melanoma[6], subungual keratoacanthoma, acquired fibrokeratoma, pyogenic granuloma, onychomatricoma and other uncommon subungual nail tumors and bone sarcomas.


The diagnosis is made by performing an X-ray examination that reveals a bony overgrowth. Surgical exploration with total or partial avulsion of the nail and resection of the overgrowth with histological evaluation confirms and treats subungual exostosis[7]. Histopathology typically reveals mature trabecular bone surrounded by a fibrocartilage cap[8]. Incomplete resections expose to the risk of local recurrences [9][10].

Xray of an ungueal exostosis
Per operative aspect of an exostosis



References

  1. Russell JD, Nance K, Nunley JR, Maher IA. Subungual exostosis. Cutis 2016;98:128–9.
  2. 2.02.12.22.32.4 DaCambra MP, Gupta SK, Ferri-de-Barros F. Subungual exostosis of the toes: a systematic review. Clinical Orthopaedics and Related Research 2014;472:1251–9.
  3. Piccolo V, Argenziano G, Alessandrini AM, Russo T, Starace M, Piraccini BM. Dermoscopy of Subungual Exostosis A Retrospective Study of 10 Patients Dermatology 2017;233:80–5
  4. Thomas L, Vaudaine M, Wortsman X, Jemec G, Drapé J. Imaging the nail unit. In: Thomas L, Baran R, editors. Baran and Dawber’s Diseases of the Nails and Their Management,. 4rth ed., London: Wiley Blackwell; 2012, p. 111–82.
  5. Daragad M, Srinivas S, Varghese J. Exostosis masquerading as a subungual wart. Indian Dermatology Online Journal 2014;5:92.
  6. Velanovich V. Subungual pigmented lesion caused by a bone spur: a mimic of a subungual melanoma. Military Medicine 1994;159:663.
  7. Basar H, Bal E, Inanmaz M, Basar B, Köse K. Protruded and nonprotruded subungual exostosis: Differences in surgical approach. Indian Journal of Orthopaedics 2014;48:49.
  8. Russell JD, Nance K, Nunley JR, Maher IA. Subungual exostosis. Cutis 2016;98:128–9.
  9. Wollina U, Baran R, Schönlebe J. Dystrophy of the Great Toenail by Subungual Exostosis and Hyperostosis: Three Case Reports with Different Clinical Presentations. Skin Appendage Disorders 2016;1:213–6.
  10. Malkoc M, Korkmaz O, Keskinbora M, Seker A, Oltulu I, Bulbul AM, et al. Surgical treatment of nail bed subungual exostosis. Singapore Medical Journal 2016;57:630–3.