Subungual Exostosis Presenting as a Cutaneous Lesion: A Diagnostic Challenge

ABSTRACT

Subungual exostosis is a benign outgrowth arising from the distal phalanx which often presents as a painful, firm mass beneath or adjacent to the nail bed. Subungual exostosis is fundamentally a bone disease that can easily be misinterpreted as a skin or nail abnormality, requiring early identification to prevent unnecessary treatment.

Beyond skin: Unveiling the bony truth of Subungual Exostosis.

A 58‐year‐old female presented with a painful subungual hyperkeratotic nodule on the right middle finger nail for the last 1 month, Figure 1. The nodule gradually progressed in size and was 1 cm in diameter. The patient denied bleeding, discharge, or any trauma before the onset of the lesion. The affected nail showed yellowish discoloration of the distal edge and onycholysis. Onychoscopic and radiological findings are shown in Figures 2 and 3, respectively.

FIGURE 1.

Solitary firm hyperkeratotic nodule underneath the nail plate of the middle finger.

FIGURE 2.

Dermoscopy shows onycholysis, white to yellow discoloration of the distal edge of the nail plate, and hyperkeratosis underneath the nail plate.

FIGURE 3.

X‐ray of hand AP view shows well‐defined bony growth on the lateral surface of the distal phalanx of the middle finger.

1. What is the Diagnosis?

1. Subungual wart

2. Pyogenic granuloma

3. Onychomycosis

4. Glomus tumor

5. Subungual exostosis

2. Discussion

The patient presented with a gradually progressive tender subungual hyperkeratotic nodule without any history of preceding trauma. Onychoscopy revealed white to yellow discoloration of the distal nail plate, onycholysis, and hyperkeratosis. The differential diagnoses included subungual wart, glomus tumor, and pyogenic granuloma. X‐ray of the hand AP view showed a well‐defined bony mass arising from the lateral surface of the distal phalanx at the tip of the middle finger, giving a clue to the diagnosis of subungual exostosis. The diagnosis of subungual exostosis was based on the clinical and radiological findings. The patient was then referred to the Orthopedic Department for surgical excision.

Subungual exostosis is a benign overgrowth of normal bone that arises from the distal phalanx, often affecting the toes [1]. Children and young adults are the most commonly affected group. The occurrence of subungual exostosis in the elderly population is rare and might pose a diagnostic challenge, as in our case. Trauma, chronic inflammation, infection, tumors, and hereditary anomalies are predisposing factors for subungual exostosis [1]. Clinically, subungual exostosis presents as a tender, firm, fixed exophytic hyperkeratotic nodule with a peripheral collarette around the base of the tumor and is frequently mistaken for onychomycosis, pyogenic granuloma, or wart [2]. Onychomycosis typically presents with diffuse nail discoloration, subungual debris, and dystrophy; however lacks an underlying bony mass. Pyogenic granuloma usually appears as a rapidly growing, friable, erythematous lesion with a tendency to bleed, in contrast to the hard, non‐friable nature of subungual exostosis. Verruca vulgaris presents as a hyperkeratotic lesion with a rough surface and shows punctate black dots representing thrombosed capillaries, without osseous proliferation. Vascular ectasia is the most common onychoscopic finding in subungual exostosis, followed by hyperkeratosis, onycholysis, and ulceration [3]. Additionally, subungual exostosis has to be differentiated from subungual osteochondromas as they are derived from fibrous tissue and enchondral ossification, respectively [1]. X‐ray shows trabeculated bone arising from the dorsal or dorsomedial aspect of the phalanges that extends distally away from the epiphysis. Tumor has a cartilaginous component that is not visualized in conventional radiography. Thus, the clinical lesion often appears larger than the radiological image. Histopathological examination of subungual exostosis shows a base of normal‐appearing trabecular bone with a fibrocartilaginous cap whereas hyaline cartilage is confluent with the underlying trabecular bone [1, 2]. Radiological imaging is sufficient for the diagnosis, and surgical excision is the treatment of choice in subungual exostosis [1].

Author Contributions

Sunil Jaiswal: conceptualization, methodology, writing – original draft, writing – review and editing. Shraddha Uprety: conceptualization, investigation, writing – original draft. Pratichya Thapa: conceptualization, methodology, supervision. Prakriti Lamichhane: conceptualization, methodology.

Funding

The authors have nothing to report.

Ethics Statement

Patient in this manuscript has given written informed consent for participation in the study and the use of their de‐identified, anonymized, aggregated data and their case details (including photographs) for publication.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.