Subungual exostosis (Dupuytren's subungual exostosis, enchondroma)

Subungual exostosis (Dupuytren’s subungual exostosis, enchondroma)

Are You Confident of the Diagnosis?

  • What you should be looking for in the history

Subungual exostosis (SE) is a benign bone and cartilage producing tumor under or adjacent to the nail unit. It was first described by Dupuytren in 1847. The nature of subungual exostosis remains controversial. The term SE is used to refer to a heterogeneous group of osteochondral tumors that affect the distal phalanx. These tumors originate in the narrow subungual space (1-2mm thick). Because misdiagnosis is common, there is often a delay in treatment.

Most commonly, they grow on the dorsomedial aspect of the distal phalanx. They enlarge over months and can break the skin and disrupt the nail unit. In some patients they are asymptomatic and present as incidental findings on X-ray. Others may complain of pain with pressure and physical activity. Often, there is a history of chronic paronychia or recurrent ingrown nail with granulation tissue. Some patients may recall trauma or previous infection, but no prior injury is required.

  • Characteristic findings on physical examination

SE is an uncommon solitary tumor. It may occur on any digit, but involves the distal phalanx of the hallux in 70-80% of cases. A hard mass is palpated under or adjacent to the nail unit. Pain is produced with pressure. Edema and erythema may affect the entire digit or just the tip. The overlying epidermis may be intact in early tumors. Older, larger tumors protrude through the skin and disrupt the nail unit (Figure 1, Figure 2).

Figure 1.

Subungual exostosis (Courtesy of Dr. Philip Fleckman)

Figure 2.

X-ray image of subungual exostosis on lateral view (Courtesy of Dr. Philip Fleckman)

The exposed exostosis may take different forms. It may present as a mass on the nail bed: smooth and dome shaped, white or red, hemorrhagic or verrucous. Various nail deformities result, depending on the location and the size of the tumor. Onycholysis, paronychia and ingrown nail are common. Due to varied clinical presentations, imaging is needed to make the diagnosis.

Four clinical types have been described based on the clinical appearance of toe and nail plate at the time of physical exam:

  • Type I or mild deformity: early distal SE causes pain upon pressure. Nail plate is intact. Nail overcurvature and subungual clavus may be present.

  • Type II or moderate deformity: exostosis is distal to the nail plate. The distal digital pulp expands upward, interfering with linear nail growth. Ingrowth, onychogryphosis and overcurvature ensue.

  • Type III: exostosis is located under the nail bed. Upward pressure by the tumor causes a pincer nail deformity, variable destruction of the nail bed and onycholysis.

  • Type IV: osseous proliferation (bone spur) of the lateral or medial ungual tuberosity results in onychocryptosis. Pain is palpated over the proximal nail fold. This variant is often associated with hallus valgus and hallus limitus. The nail folds are often affected with non-healing granulation tissue.

  • Expected results of diagnostic studies

The lateral radiographs of the affected digit are diagnostic. They demonstrate a bony outgrowth emanating from the dorsal or dorsomedial aspect of the distal phalanx. SE is typically not continuous with the underlying bone, contrary to osteochondroma. The radiographs often underestimate the actual tumor size due to the radiolucency of the fibrocartilaginous cap.

Ultrasound with Doppler studies reveals a hypovascular, well-circumscribed, hyperechoic mass with calcifications and a hypoechoic fibrocartilaginous cap. Magnetic resonance imaging demonstrates the effect of the tumor on the surrounding tissue. The fibrocartilaginous cap is hypointense, contrary to the hyaline cartilage in osteochondroma. Histopathology shows a fibrocartilaginous cap over a trabecular bony stalk. The ossification begins from the base; more mature lesions have a thinner cap.

  • Diagnosis confirmation

It is difficult to distinguish subungual exostoses from subungual osteochondromas both clinically and histologically. In contrast to exostoses, osteochondromas have a hyaline cap and are continuous with the underlying cortical bone. The differential diagnosis includes benign subungual tumors (subungual osteochondroma, glomus tumor, pyogenic granuloma, verruca vulgaris, fibroma), malignant subungual tumors (subungual metastasis, amelanotic melanoma, squamous cell carcinoma, keratoacanthoma), onychomycosis, onychocryptosis, chronic paronychia and pincer nail deformity.

Who is at Risk for Developing this Disease?

SE is a sporadic, benign tumor. It may occur in the pediatric population and in older age groups. Some studies show no sex predilection, while other studies show a 2:1 female predominance. Duration of symptoms is typically a few months, but may be as long as several years. SE is a solitary tumor with few multiple cases reported. Familial cases and metastasis have not been reported. Seventy-seven percent of subungual exostoses develop on the hallux, 10% on other toes and 13% on fingers. The risk factors have not been established, but trauma, previous surgery, recurrent infection, high-heeled narrow shoes and first-ray disorders (hallux limitus and hallux vulgas) have been implicated.

What is the Cause of the Disease?

  • Etiology and pathophysiology

The pathogenesis of subungual exostosis is unknown, but current theories include trauma, infection, tumor, hereditary abnormality, or activation of a cartilaginous cyst. While there is no conclusive evidence, many believe that subungual exostosis is a reactive response to microtrauma. According to this theory, trauma induces the growth of fibroblasts, followed by cartilage metaplasia and ossification. Since the translocation t(X;6)(q22;q13-14) has been associated with subungual exostoses, it may be a true neoplasm rather than a reactive process in response to trauma. In addition, molecular studies have localized the breakpoints on chromosomes 6 and X to COL12A1 and COL4A5 genes. It has been shown that this translocation leads to deregulated expression of insulin receptor substrate 4 (IRS4). The exact role of IRS4 is not understood. IRS proteins mediate signals from receptors such as insulin and insulin-like growth factor 1. It is unclear how this byproduct results in the formation of subungual exostosis.

Systemic Implications and Complications

Subungual exostosis can destroy the surrounding soft tissue and nail unit. It is not associated with any systemic complications or diseases.

Treatment Options


--High box shoe

--Nail plate trimming/avulsion

Surgical exostectomy with nail bed repair

--Direct access through the nail bed/nail bed reconstruction

--Indirect access through a fish-mouth incision

Optimal Therapeutic Approach for this Disease

Medical therapy is not curative and provides temporary relief of symptoms. This includes the use of high-box shoe and proper nail trimming/avulsion.

The surgical removal of the exostosis is curative. The overriding principle is to balance complete lesional excision and sparing the underlying nail bed to avoid complications. The surgeon should be knowledgeable about the nail anatomy. Surgery requires meticulous aseptic measures. Excision is performed with a nerve block, except for the very young, who will require general anesthesia.

Various reports detail the surgical approach to excision. A combination of techniques is required to remove the exostosis and repair the nail abnormality. The surgical approach is based on the clinical presentation. Exostosis can be excised through the nail bed (direct) or via a fish-mouth incision around the nail plate (indirect). The direct technique is often employed in the presence of a nail bed defect. Fish-mouth incision allows lifting up the nail bed to expose exostosis.

Variable nail plate abnormalities will lend to different surgical corrections and should be addressed at the time of exostectomy. Nail plate correction may require a combination of approaches, from partial matricectomy for onychocryptosis to complete matricectomy or debulking of a hypertrophic distal pulp.

Recurrence rate is estimated at 10 to 20% post surgery. Complete removal of the fibrocartilaginous cap and curettage of the base increase the cure rate. The direct approach is believed to allow for better visualization of the exostosis and complete removal of the cap, leading to a higher cure rate.

The post-operative nail appearance in 16 cases of subungual exostoses have been studied. The patients were followed for an average of 36.6 months. Onycholysis (secondary to nail bed grafting) and ingrowth were the most common complications.

Patient Management

A complete exostectomy is curative with a low rate of recurrence. Good surgical techniques are necessary for optimal results. However, permanent nail deformity may result, depending on the size and location of the exostosis.

Unusual Clinical Scenarios to Consider in Patient Management

The diagnosis of subungual exostosis is often delayed. It can present with various nail deformities (such as onycholysis, onychocryptosis or paronychia) that can impede the accurate diagnosis. A detailed exam, high level of suspicion and radiography allow for the correct diagnosis.

What is the Evidence?

Baek, HJ, Lee, SJ, Cho, KH, Choo, HJ, Lee, SM, Lee, YH. "Subungual tumors: clinicopathologic correlation with US and MR image findings". Radiographics. vol. 30. 2010. pp. 1621-36.

(The article reviews the anatomy of the nail unit and discusses and illustrates a variety of subungual tumors. It concludes that magnetic resonance (MR) and ultrasonography are useful in categorizing subungual tumors especially when combined with clinical and pathological information. There is some overlap between the information obtained from MR and US. High resolution ultrasonography with color Doppler studies provides information about tumor size, location, shape and internal characteristics, but cannot identify the tissue. MR imaging is helpful when US findings are not diagnostic.)

Garcia Carmona, FJ, Pascual Huerta, J, Fernandez Morato, D. "A proposed subungual exostosis clinical classification and treatment plan". J Am Podiatr Med Assoc. vol. 99. 2009. pp. 519-24.

(The authors propose a new classification system for subungual exostosis based on clinical signs and symptoms. A therapeutic algorithm for each clinical presentation is offered.)

Lee, SK, Jung, MS, Lee, YH, Gong, HS, Kim, JK, Baek, GH. "Two distinctive subungual pathologies: Subungual exostosis and subungual osteochondroma". Foot Ankle Int. vol. 28. 2007. pp. 595-601.

(11 patients with subungual masses were surgically treated and their findings were compared. The authors conclude that subungual exostosis is distinct from subungual osteochondroma clinically, developmentally, radiographically and histologically.)

Storlazzi, CT, Wozniak, A, Panagopoulos, I, Sciot, R, Mandahl, N, Mertens, F. "Rearrangement of the COL12A1 and COL4A5 genes in subungual exostosis: molecular cytogenetic delineation of the tumor-specific translocation t(X;6)(q13-14;q22)". Int. J. Cancer. vol. 118. 2006. pp. 1972-76.

(After six cases of subungual exostosis were reported to have the same t(X;6) translocation, these investigators set out to study the molecular consequence of this gene rearrangement. Using metaphase and interphase FISH analyses, they showed the clustering of chromosomal breakpoints to collagen genes: COL12A1 and COL4A5.)

Mertens, F, Moller, E, Mandahl, N, Picci, P, Perez-Atayde, AR, Samson, I. "The t(X;6) in subungual exostosis results in transcriptional deregulation of the gene for insulin receptor substrate 4". Int J Cancer. vol. 128. 2011. pp. 487-91.

(Authors showed that t(X;6) translocation results in upregulation of IRS4 gene. IRS proteins affect cell growth and survival by mediating signals from receptors such as the insulin and insulin-like growth factor 1.)

Dumontier, CA, Abimelec, P. "Nail unit enchondromas and osteochondromas: a surgical approach". Dermatol Surg. vol. 27. 2001. pp. 274-9.

(Authors discuss surgical treatment of subungual exostoses and enchondromas.)

Suga, H, Mukouda, M. "Subungual exostosis: a review of 16 cases focusing on postoperative deformity of the nail". Ann Plast Surg. vol. 55. 2005. pp. 272-5.

(Postoperative nail changes were studied in 16 patients who underwent surgery for subungual exostosis. When possible, a fish-mouth-type incision spares the nail unit. Nail bed reconstruction may be indicated when destroyed by the tumor.)

Choi, CM, Cho, HR, Lew, BL, Sim, WY. "Subungual exostosis treated with an in situ thin split-thickness toenail bed graft". Dermatological Therapy. vol. 24. 2011. pp. 452-4.

(Treatment with split thickness skin graft.)

DaCambra, MP, Gupta, SK, Ferri-de-Barros. "Subungual exostosis of the toes: a systematic review". Clin Orthop Relat Res. vol. 472. 2014 Apr. pp. 1251-9.

(This manuscript reviews the clinical presentation of subungual exostoses and treatment strategies.)
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