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Subungual Exostosis

Last updated June 8, 2021

Reviewed by: Lester Fahrner, MD

Approved by: Krish Tangella MD, MBA, FCAP

Subungual Exostosis is a tumor of the nail affecting the tissue beneath the nail base, known as the nail matrix. It is the region from where the nail forms and grows.

What are the other Names for this Condition? (Also known as/Synonyms)

  • Exostosis of Nail Bed
  • Subungual Exostosis of Finger
  • Subungual Exostosis of Toe

What is Subungual Exostosis? (Definition/Background Information)

  • Subungual Exostosis is a tumor of the nail affecting the tissue beneath the nail base, known as the nail matrix. It is the region from where the nail forms and grows. It can affect any of the finger and toe; but since it occurs under the nail, it is termed subungual
  • Subungual Exostosis is not an osteochondroma (a type of a benign bone tumor). It is believed to develop due to genetic mutations and chromosomal aberrations
  • The tumor is mostly observed in teens and young adults. Subungual Exostosis typically involves the large toe or the index finger. The tumor is mostly slow-growing and can cause pain; it can even destroy the nail bed in some cases
  • Once a definitive diagnosis has been made, Subungual Exostosis is surgically excised. The prognosis of Subungual Exostosis is excellent with appropriate surgical treatment

Who gets Subungual Exostosis? (Age and Sex Distribution)

  • Subungual Exostosis is observed infrequently in individuals of any age. However, it is most commonly seen in children, adolescents, and young adults in the 10-30 years of age
  • A slight predilection for males is observed, even though both males and females are affected. However, some studies indicate a preference for females
  • All racial and ethnic groups are at equal risk for tumor formation

What are the Risk Factors for Subungual Exostosis? (Predisposing Factors)

In a majority of the cases, the risk factors for Subungual Exostosis are unknown. However, in some rare cases, the following genetic conditions are known to be risk factors:

  • Multiple exostosis syndrome
  • Multiple exostosis with mental retardation syndrome

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Subungual Exostosis? (Etiology)

The cause of development of Subungual Exostosis is due to certain genetic abnormalities.

  • Current studies have shown that the chromosomal translocation t(X;6)(q24-26;q15-25) is observed in many cases. This may be the only genetic abnormality observed in the tumor
  • The genes involved in the above chromosomal anomaly includes the following:
    • COL12A1
    • COL4A5
    • IRS4
  • Some studies have detected the chromosomal translocation t(X;6)(q22;q13-14)

Earlier, researchers believed that a history of infection or trauma contributed towards tumor development, and hence, the tumor formed as a reactive process.

What are the Signs and Symptoms of Subungual Exostosis?

The following signs and symptoms of Subungual Exostosis may be observed:

  • The presence of a typically slow-growing tumor beneath the nail
  • The tumor presents pain (in many cases) and swelling
  • In rare cases, the growth is rapid, thereby rising a concern for malignancy
  • The lesion may be present either in the finger or toe. It occurs in the tip of the digit that is involved
  • The most common site of the tumor is the large or great toe; followed by the index and middle finger
  • Subungual Exostosis involves the bone and cartilage at the affected site
  • The tumor can cause deformation of the overlying nail
  • The nail may become brittle and crack/break while remaining attached at the base

How is Subungual Exostosis Diagnosed?

The diagnosis of Subungual Exostosis may be undertaken through the following tests and exams:

  • A thorough physical exam and complete evaluation of medical history
  • Radiological imaging studies of the affected finger or toe, via X-ray, MRI or CT scans
  • A tissue biopsy of the tumor is performed and sent to a laboratory for a pathological examination. A pathologist examines the biopsy under a microscope. After putting together clinical findings, special studies on tissues (if needed) and with microscope findings, the pathologist arrives at a definitive diagnosis. Examination of the biopsy under a microscope by a pathologist is considered to be gold standard in arriving at a conclusive diagnosis
  • A differential diagnosis to rule out the following tumors is normally undertaken:
    • Subungual osteogenic melanoma
    • Bizarre parosteal osteochondromatous proliferation (Nora lesion)

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Subungual Exostosis?

Subungual Exostosis may cause the following complications:

  • Emotional stress
  • Severe pain
  • The tumor can destroy the nail bed
  • The removal of the tumor may result in deformed nail (onychodystrophy); permanent nail deformity
  • The tumor can rarely recur after its surgical removal

How is Subungual Exostosis Treated?

The treatment of Subungual Exostosis may involve the following measures:

  • The healthcare provider may recommend a ‘wait and watch’ approach for small, asymptomatic tumors
  • Simple excision and complete removal of the tumor and the overlying nail is the most effective treatment. The nail usually grows back after a certain period, in most cases
  • Follow-up care with regular screening and check-ups are important, since some tumors are known to return

How can Subungual Exostosis be Prevented?

Currently, it is not possible to prevent the formation of Subungual Exostosis.

What is the Prognosis of Subungual Exostosis? (Outcomes/Resolutions)

  • With appropriate treatment, the prognosis of Subungual Exostosis is typically excellent, since the tumors are benign in nature
  • The risk of recurrence is related to surgery. With complete excision and removal, the tumor does not recur; while, with incomplete tumor removal, there is a minimal risk for recurrence

Additional and Relevant Useful Information for Subungual Exostosis:

Please visit our Cancer & Benign Tumors Health Center for more physician-approved health information:


What are some Useful Resources for Additional Information?

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Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: April 6, 2017
Last updated: June 8, 2021